Consumer medicine information

Retrovir

Zidovudine

BRAND INFORMATION

Brand name

Retrovir Capsules and Syrup

Active ingredient

Zidovudine

Schedule

SUMMARY CMI

RETROVIR

Consumer Medicine Information (CMI) summary

The full CMI on the next page has more details. If you are worried about using this medicine, speak to your doctor or pharmacist.

1. Why am I taking RETROVIR?

RETROVIR contains the active ingredient zidovudine. RETROVIR is used, alone or in combination with other antiretrovirals, to slow down the progression of human immunodeficiency virus (HIV) infection which can lead to Acquired Immune Deficiency Syndrome (AIDS) and other related illnesses (e.g. AIDS-related Complex (ARC)).

For more information, see Section 1. Why am I taking RETROVIR? in the full CMI.

2. What should I know before I take RETROVIR?

Do not use if you have ever had an allergic reaction to RETROVIR or any of the ingredients listed at the end of the CMI.

Talk to your doctor if you have any other medical conditions, take any other medicines, or are pregnant or plan to become pregnant or are breastfeeding.

For more information, see Section 2. What should I know before I take RETROVIR? in the full CMI.

3. What if I am taking other medicines?

Some medicines may interfere with RETROVIR and affect how it works.

A list of these medicines is in Section 3. What if I am taking other medicines? in the full CMI.

4. How do I use RETROVIR?

The usual dosage of RETROVIR is 500 mg to 600 mg daily taken as a divided dose (can be between two and five separate doses).
A daily dose of 1000 mg taken in two divided doses can also be prescribed.
Swallow the capsules with some water.

More instructions can be found in Section 4. How do I take RETROVIR? in the full CMI.

5. What should I know while taking RETROVIR?

Things you should do	Remind any doctor, dentist or pharmacist you visit that you are taking RETROVIR. For as long as you are taking RETROVIR, your doctor will arrange for you to have regular blood tests to check for side effects. Keep in contact with your doctor and don't stop taking RETROVIR without talking to your doctor.
Things you should not do	Do not stop using this medicine suddenly or change the dose without talking to your doctor. Do not take this medicine to treat any other complaints.
Driving or using machines	Be careful before you drive or use any machines or tools until you know how RETROVIR affects you.
Looking after your medicine	Store RETROVIR below 30°C in the pack out of direct light. Keep this medicine in the pack until it is time to take it.

For more information, see Section 5. What should I know while taking RETROVIR? in the full CMI.

6. Are there any side effects?

Side effects that have been reported include body odour, chills, increased sensitivity to pain, back pain, chest pain, weakness, weight loss, loss of appetite, generally feeling unwell, feeling faint and fainting, constipation, blood in the stool, difficulty in swallowing, mouth ulcers, bleeding gums, heartburn, vomiting, nausea, nose bleeds, muscle aches or pains, muscle spasms or twitching, confusion, depression, nervousness, loss of mental clarity, dizziness, seizures, headache, sleeplessness, cough, sore throat, hay fever, acne, itchiness, changes in nail, skin or mouth colour, vision problems, sensitivity to light, hearing loss, passing too much urine and increased frequency of urination.

For more information, including what to do if you have any side effects, see Section 6. Are there any side effects? in the full CMI.

FULL CMI

RETROVIR

Active ingredient(s): zidovudine

Consumer Medicine Information (CMI)

This leaflet provides important information about using RETROVIR. You should also speak to your doctor or pharmacist if you would like further information or if you have any concerns or questions about using RETROVIR.

Where to find information in this leaflet:

1. Why am I taking RETROVIR?
2. What should I know before I take RETROVIR?
3. What if I am taking other medicines?
4. How do I take RETROVIR?
5. What should I know while taking RETROVIR?
6. Are there any side effects?
7. Product details

1. Why am I taking RETROVIR?

RETROVIR contains the active ingredient zidovudine. RETROVIR belongs to a group of medicines called antiretrovirals.

RETROVIR is used, alone or in combination with other antiretrovirals, to slow down the progression of human immunodeficiency virus (HIV) infection which can lead to Acquired Immune Deficiency Syndrome (AIDS) and other related illnesses (e.g. AIDS-related Complex (ARC)).

RETROVIR does not cure AIDS or HIV infection however it slows down production of HIV in the body. In this way it stops ongoing damage to the body's immune system which fights infection.

You can still pass on HIV when taking this medicine through sexual activity or through passing on blood or bodily secretions which carry the HIV virus, although the risk is lowered by taking antiretroviral therapy.

You should use proper precautions to prevent this from occurring. Discuss with your doctor the precautions needed to avoid infecting other people.

While taking RETROVIR and/or any other therapy for HIV, you may continue to develop other infections and other complications of HIV infection. You should keep in regular contact with your doctor.

2. What should I know before I take RETROVIR?

Warnings

Do not use RETROVIR if:

you are allergic to zidovudine, or any of the ingredients listed at the end of this leaflet.
Always check the ingredients to make sure you can use this medicine.
you weigh less than 30 kg
you have a reduced red blood cell count (anaemia) or white blood cell count (neutropenia)

Check with your doctor if you:

have any other medical conditions
take any medicines for any other condition
are allergic to any other foods, dyes, preservatives or medicines

During treatment, you may be at risk of developing certain side effects. It is important you understand these risks and how to monitor for them. See additional information under Section 6. Are there any side effects?

Pregnancy and breastfeeding

Talk to your doctor if you are pregnant or intend to become pregnant.

Talk to your doctor if you are breastfeeding or intend to breastfeed.

Your doctor can discuss with you the benefits and risks of taking RETROVIR whilst pregnant or breastfeeding.

Symptoms of infection and inflammation

People with advanced HIV infection (AIDS) have weak immune systems and are more likely to develop serious infections (opportunistic infections). When they start treatment, the immune system becomes stronger and so the body starts to fight infections.

Symptoms of infection and inflammation may develop, caused by either:

old, hidden infections flaring up at the body fights them
the immune system attacking healthy body tissue (autoimmune disorders)

The symptoms of autoimmune disorders may develop many months after you start taking medications to treat your HIV infection.

Symptoms may include:

muscle weakness and/or muscle pain
joint pain or swelling
weakness beginning in the hands or feet and moving towards the trunk of the body
palpitations or tremor
hyperactivity (excessive restlessness and movement)

If you get symptoms of infection or if you notice any of the symptoms above, tell your doctor immediately. Do not take other medicines for the infection without your doctor's advice.

3. What if I am taking other medicines?

Tell your doctor or pharmacist if you are taking any other medicines, including any medicines, vitamins or supplements that you buy without a prescription from your pharmacy, supermarket or health food shop.

Some medicines may interfere with RETROVIR and affect how it works.

If you take ribavirin (e.g. Ibavyr) and RETROVIR together it may cause or worsen anaemia (low red blood cells). Tell your doctor if you notice symptoms of anaemia such as tiredness and shortness of breath.

Tell your doctor if you are taking any of the medicines below:

medicines used to treat pain including paracetamol, aspirin, codeine, morphine, methadone, indomethacin, ketoprofen, naproxen
medicines used in epilepsy including phenytoin
medicines used to treat anxiety and insomnia including oxazepam, lorazepam
cimetidine, a medicine used to treat heartburn, stomach ulcers
clofibrate, a medicine used to treat high cholesterol, high triglycerides
probenecid, a medicine used in the treatment of gout
antimicrobial medicines such as pentamidine
medicines used to treat parasite infections including pyrimethamine, dapsone
antimicrobial medicines including atovaquone
amphotericin, flucytosine, medicines used to treat fungal infections
other antiviral medicines such as ganciclovir, interferon
clarithromycin, an antibacterial medicine
medicines used in the treatment of cancer including vincristine, vinblastine and doxorubicin

Check with your doctor or pharmacist if you are not sure about what medicines, vitamins or supplements you are taking and if these affect RETROVIR.

4. How do I take RETROVIR?

How much to take

The usual dosage of RETROVIR is 500 mg to 600 mg daily taken as a divided dose. This may be taken across two to five separate doses.
A daily dose of 1000 mg in two divided doses can also be prescribed.
Follow the instructions provided by your doctor or pharmacist and use RETROVIR until your doctor tells you to stop.

How to take RETROVIR

Swallow the capsule whole with a drink of water.

If you forget to take RETROVIR

RETROVIR should be used regularly at the same time each day.

If it is almost time for your next dose, skip the dose you missed and take your next dose when you are meant to. Otherwise, take it as soon as you remember and then go back to taking your medicine as you would normally.

Do not take a double dose to make up for the dose you missed.

If you take too much RETROVIR

If you think that you have taken too much RETROVIR, you may need urgent medical attention.

You should immediately:

phone the Poisons Information Centre
(by calling 13 11 26), or
contact your doctor, or
go to the Emergency Department at your nearest hospital.

You should do this even if there are no signs of discomfort or poisoning.

5. What should I know while taking RETROVIR?

Things you should do

Ensure you have blood tests when you are meant to. It is important that your doctor monitors your health and checks the levels of red and white blood cells. If you develop anaemia or neutropenia your doctor may reduce your dose or stop RETROVIR.

Tell your doctor straight away if you:

become pregnant or intend to become pregnant
have not taken RETROVIR as intended

Remind any doctor, dentist or pharmacist you visit that you are using RETROVIR.

This is especially important for any medicines that might have an effect on your liver, kidneys, red or white blood cells or other cells in the body.

Stay in regular contact with your doctor

RETROVIR helps to control your condition, but it is not a cure for HIV infection. You need to keep taking it everyday to stop your illness from getting worse. Because RETROVIR does not cure HIV infections, you may still develop other infections and illnesses linked to HIV.

Things you should not do

Do not stop taking this medicine suddenly or change the dose.
Do not give this medicine to anyone else, even if their symptoms seem similar to yours.
Do not use this medicine to treat any other complaints unless your doctor tells you to.

Driving or using machines

Be careful before you drive or use any machines or tools until you know how RETROVIR affects you.

Looking after your medicine

Keep RETROVIR in the pack until it is time to take it.

Store it in a cool dry place (below 30°C) away from moisture, heat or sunlight; for example, do not store it:

in the bathroom or near a sink, or
in the car or on window sills.

Keep it where young children cannot reach it.

Getting rid of any unwanted medicine

If you no longer need to use this medicine or it is out of date, take it to any pharmacy for safe disposal.

Do not use this medicine after the expiry date.

6. Are there any side effects?

All medicines can have side effects. If you do experience any side effects, most of them are minor and temporary. However, some side effects may need medical attention.

Within the first few weeks of treatment with anti-HIV medicines, some people, particularly those that have been HIV positive for some time, may develop inflammatory reactions (e.g. pain, redness, swelling, high temperature) which may resemble an infection and may be severe. It is thought that these reactions are caused by a recovery in the body's ability to fight infections, previously suppressed by HIV.

If you become concerned about any new symptoms, or any changes in your health after starting HIV treatment, discuss with your doctor immediately.

See the information below and, if you need to, ask your doctor or pharmacist if you have any further questions about side effects.

Less serious side effects

Less serious side effects

What to do

body odour
chills
increased sensitivity to pain, back pain, enlarged glands, chest pain
weakness
weight loss, loss of appetite
generally feeling unwell
widening of blood vessels leading to low blood pressure and feeling faint
constipation, gas from the stomach or bowel, blood in the stool
difficulty in swallowing, mouth ulcers, bleeding gums
heartburn
vomiting, nausea
nose bleeds
muscle aches or pains, muscle shaking or spasms or twitching
confusion, depression, nervousness, fainting, loss of mental clarity, dizziness, seizures, headache, sleeplessness
cough, sore throat, hay fever, sinus problems, hoarseness
acne, itchiness, changes in nail, skin or mouth colour
vision problems, sensitivity to light
hearing loss
passing too much urine or increased frequency of urination

Speak to your doctor if you have any of these less serious side effects and they worry you.

Serious side effects

Serious side effects

What to do

reduced red blood cell count (anaemia)
reduced white blood cell count (neutropenia)

The frequency and severity of anaemia and neutropenia are greater in patients with advanced HIV disease or in patients who start taking RETROVIR in the later stages of HIV disease.

swelling of the lips, tongue, wheezing or difficulty breathing, rash, hives on the skin. These are all signs of an allergic reaction.

Treatment with RETROVIR may cause a loss of fat from the legs, arms and face (lipoatrophy). If this occurs tell your doctor and they will assess if you should stop taking RETROVIR and your HIV treatment be changed. If you stop taking RETROVIR it may take several months to see any lost fat return and you might not regain it all.

If you are taking medication for HIV and become unwell with fast breathing, stop taking RETROVIR and talk to your doctor immediately. This might be a condition known as ‘lactic acidosis’. The fast breathing is due to high acid levels in the blood. Your liver may not be working properly and gets big and fatty and can be life threatening. This illness occurs more often in women than men.

Call your doctor straight away, or go straight to the Emergency Department at your nearest hospital if you notice any of these serious side effects.

Tell your doctor or pharmacist if you notice anything else that may be making you feel unwell.

Other side effects not listed here may occur in some people.

Reporting side effects

After you have received medical advice for any side effects you experience, you can report side effects to the Therapeutic Goods Administration online at www.tga.gov.au/reporting-problems. By reporting side effects, you can help provide more information on the safety of this medicine.

Always make sure you speak to your doctor or pharmacist before you decide to stop taking any of your medicines.

7. Product details

This medicine is only available with a doctor's prescription.

What RETROVIR capsules contain

Active ingredient (main ingredient)	zidovudine
Other ingredients (inactive ingredients)	gelatin indigo carmine (250 mg capsules only) magnesium stearate maize starch microcrystalline cellulose polysorbate 80 sodium starch glycollate titanium dioxide

What RETROVIR syrup contains

Active ingredient (main ingredient)	zidovudine
Other ingredients (inactive ingredients)	citric acid glycerol maltitol solution sodium saccharin sodium benzoate Strawberry Flavour PHL-134189 White Sugar Flavour DA13780 purified water
Potential allergens	maltitol solution sodium benzoate saccharin sodium

Do not take this medicine if you are allergic to any of these ingredients.

What RETROVIR looks like

RETROVIR capsules are available in 2 strengths:

100 mg capsules: opaque white cap and body coded GSYJU. Available in blister packs of 100 capsules.
AUST R 178383
250 mg capsules: opaque blue cap and opaque white body coded GSJV2. Available in blister packs of 40 or 60 capsules.
AUST R 178384

Not all pack sizes may be marketed.

RETROVIR syrup is a pale yellow, strawberry flavoured liquid and is supplied in a 200 mL bottle with a syringe, syringe adaptor and a plastic cap.

AUST R 41043

Who distributes RETROVIR

ViiV Healthcare Pty Ltd
Level 4, 436 Johnson Street
Abbotsford VIC 3067
Australia

Trademarks are owned by or licenced to the ViiV Healthcare group of companies.

This leaflet was prepared October 2022

Version 9.0

Published by MIMS March 2023

BRAND INFORMATION

Brand name

Retrovir Capsules and Syrup

Active ingredient

Zidovudine

Schedule

1 Name of Medicine

Zidovudine.

2 Qualitative and Quantitative Composition

Zidovudine is a white to off-white, odourless crystalline solid.

Retrovir Capsules 100 mg.

Each capsule contains zidovudine 100 mg.

Retrovir Capsules 250 mg.

Each capsule contains zidovudine 250 mg.

Retrovir Syrup.

Each 5 mL contains zidovudine 50 mg, sodium benzoate, saccharin sodium, maltitol solution.
For the full list of excipients, see Section 6.1 List of Excipients.

3 Pharmaceutical Form

Retrovir Capsules 100 mg.

Opaque white cap and body coded GSYJU.

Retrovir Capsules 250 mg.

Opaque blue cap and opaque white body coded GSJV2.

Retrovir Syrup.

Pale yellow, strawberry flavoured.

4 Clinical Particulars

4.1 Therapeutic Indications

Retrovir (zidovudine) is indicated for use in the treatment of HIV infection, alone and in combination with other antiretroviral therapies. The optimal dosage for this indication has not been established.

4.2 Dose and Method of Administration

Adults weighing at least 30 kg.

A broad range of dosage regimens has been employed; a daily dose of 500-600 mg in two to five divided doses has been used commonly worldwide.

Dosage in combination therapy.

Retrovir may be administered separately or with other antiretroviral therapies (see Section 5.1 Pharmacodynamic Properties, Clinical trials, Combination therapy).

Monitoring of patients.

Haematologic toxicities appear to be related to pretreatment bone marrow reserve and to dose and duration of therapy. In patients with poor bone marrow reserve, particularly in patients with advanced symptomatic HIV disease, frequent monitoring of haematologic indices is recommended to detect serious anaemia or granulocytopenia (see Section 4.4 Special Warnings and Precautions for Use). In patients who experience haematologic toxicity, reduction in haemoglobin may occur as early as 2 to 4 weeks, and granulocytopenia usually occurs after 6 to 8 weeks.

Dose adjustment.

Significant anaemia (haemoglobin of < 7.5 g/dL or reduction of > 25% of baseline) and/or significant granulocytopenia (granulocyte count of < 750/mm³ or reduction of > 50% from baseline) require a dose interruption until evidence of marrow recovery is observed (see Section 4.4 Special Warnings and Precautions for Use). For less severe anaemia or granulocytopenia, a reduction in daily dose may be adequate. In patients who develop significant anaemia, dose modification does not necessarily eliminate the need for transfusion. If marrow recovery occurs following dose modification, gradual increases in dose may be appropriate depending on haematologic indices and patient tolerance.

Dosage in the elderly.

No specific data are available, however, special care is advised in this age group due to age-associated changes such as the decrease in renal function and alterations in haematological parameters.

Dosage in renal impairment.

Compared to healthy subjects, patients with advanced renal failure have a 50% higher maximum plasma concentration of zidovudine. Systemic exposure (measured as area under the zidovudine concentration-time curve) is increased 100%; the half-life is not significantly altered. In renal failure there is substantial accumulation of the major glucuronide metabolite compared to healthy volunteers (see Table 1) but this does not appear to cause toxicity.

Patients with advanced renal failure should receive Retrovir at the lower end of the dosage range. Haematological parameters and clinical response may influence the need for subsequent dosage adjustment. Haemodialysis and peritoneal dialysis have no significant effect on zidovudine elimination. In a small number of patients haemodialysis would appear to be more efficient in eliminating the glucuronide metabolite than peritoneal dialysis.

Dosage in hepatic impairment.

Limited data in patients with cirrhosis suggest that accumulation of zidovudine may occur in patients with hepatic impairment because of decreased glucuronidation. Dosage adjustments may be necessary but precise recommendations cannot be made at present. If monitoring of plasma zidovudine levels is not feasible, physicians will need to pay particular attention to signs of intolerance and increase the interval between doses as appropriate.

Dosage adjustments in recipients of combination therapy.

For recipients of combination antiretroviral therapy, dosage adjustments for the drugs should follow guidelines for the individual drug. For severe adverse events, those in which the causative drug is unclear, or those persisting after dose interruption or reduction of one drug, the other drug(s) should also be interrupted or dose-reduced. Physicians should refer to the complete product information for the respective antiretroviral drug for a description of the associated adverse reactions.

4.3 Contraindications

Retrovir preparations are contraindicated for patients who have potentially life-threatening allergic reactions to any of the components of the formulation.
Retrovir should not be given to patients with abnormally low neutrophil counts (less than 0.75 x 10⁹/L) or abnormally low haemoglobin levels (less than 7.5 g/dL or 4.65 mmol/L).

4.4 Special Warnings and Precautions for Use

Warnings.

Therapy with Retrovir (zidovudine) is commonly associated with haematologic toxicity including granulocytopenia and severe anaemia requiring transfusions, particularly in patients with advanced HIV disease.

Precautions.

Patients receiving zidovudine or any other antiretroviral therapy may continue to develop opportunistic infections and other complications of HIV infection, and therefore should remain under close clinical observation by physicians experienced in the treatment of patients with HIV associated diseases.
The full safety and efficacy profile of zidovudine has not been completely defined, particularly in regard to prolonged use.
Zidovudine should be used with extreme caution in patients who have bone marrow compromise evidenced by a granulocyte count < 1000/mm³ or haemoglobin < 9.5 g/dL. In all of the placebo-controlled studies, but most frequently in patients with advanced symptomatic HIV disease, anaemia and granulocytopenia were the most significant adverse events observed (see Section 4.8 Adverse Effects (Undesirable Effects)).
There have been reports of pancytopenia associated with the use of zidovudine, which was reversible in most instances after discontinuance of the drug.
Significant anaemia most commonly occurred after 4 to 6 weeks of therapy and in many cases required dose adjustment, discontinuation of zidovudine, and/or blood transfusions. Frequent (at least every 2 weeks) blood counts are strongly recommended in patients with advanced HIV disease taking zidovudine. For asymptomatic HIV-infected individuals and patients with early HIV disease, most of whom have better marrow reserve, blood counts may be obtained less frequently, depending upon the patient's overall status. If anaemia or granulocytopenia develops, dosage adjustments may be necessary (see Section 4.2 Dose and Method of Administration).
Sensitisation reactions, including anaphylaxis in one patient, have been reported in individuals receiving zidovudine therapy. Patients experiencing a rash should undergo medical evaluation.
If zidovudine is co-administered with other drugs metabolised by glucuronidation, careful thought should be given to the possibilities of interactions, because the toxicity of either drug may be potentiated (see Section 4.5 Interactions with Other Medicines and Other Forms of Interactions). Zidovudine recipients who used paracetamol during the controlled trial in advanced HIV disease had an increased incidence of granulocytopenia, which appeared to be correlated with the duration of paracetamol use.

Lipoatrophy.

Treatment with zidovudine has been associated with loss of subcutaneous fat. The incidence and severity of lipoatrophy are related to cumulative exposure. This fat loss, which is most evident in the face, limbs and buttocks, may be only partially reversible and improvement may take several months when switching to a zidovudine-free regimen. Patients should be regularly assessed for signs of lipoatrophy during therapy with zidovudine and other zidovudine containing products (Combivir and Trizivir), and if feasible therapy should be switched to an alternative regimen if there is suspicion of lipoatrophy development.

Serum lipids and blood glucose.

Serum lipid and blood glucose levels may increase during antiretroviral therapy. Disease control and lifestyle changes may also be contributing factors. Consideration should be given to the measurement of serum lipids and blood glucose. Lipid disorders should be managed as clinically appropriate.

Lactic acidosis and severe hepatomegaly with steatosis.

Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of antiretroviral nucleoside analogues either alone or in combination, including zidovudine. A majority of these cases have been in women.
Clinical features which may be indicative of the development of lactic acidosis include generalised weakness, anorexia and sudden unexplained weight loss, gastrointestinal symptoms and respiratory symptoms (dyspnoea and tachypnoea).
Caution should be exercised when administering zidovudine, particularly to those with known risk factors for liver disease. Treatment with zidovudine should be suspended in any patient who develops clinical or laboratory findings suggestive of lactic acidosis with or without hepatitis (which may include hepatomegaly and steatosis even in the absence of marked transaminase elevations).

Immune reconstitution syndrome (IRIS).

In HIV-infected patients with severe immune deficiency at the time of initiation of anti-retroviral therapy (ART), an inflammatory reaction to asymptomatic or residual opportunistic infections may arise and cause serious clinical conditions, or aggravation of symptoms. Typically, such reactions have been observed within the first few weeks or months of initiation of ART. Relevant examples are cytomegalovirus retinitis, generalised and/or focal mycobacterial infections and Pneumocystis jiroveci (P. carinii) pneumonia. Any inflammatory symptoms must be evaluated without delay and treatment initiated when necessary. Autoimmune disorders (such as Graves' disease, polymyositis and Guillain-Barre syndrome) have also been reported to occur in the setting of immune reconstitution, however the time to onset is more variable, and can occur many months after initiation of treatment and sometimes can be an atypical presentation.

Mitochondrial dysfunction.

Nucleoside and nucleotide analogues have been demonstrated in vitro and in vivo to cause a variable degree of mitochondrial damage. There have been reports of mitochondrial dysfunction in HIV-negative infants exposed in utero and/or post-natally to nucleoside analogues. The main adverse events reported are haematological disorders (anaemia, neutropenia), metabolic disorders (hyperlactatemia, hyperlipasemia). These events are often transitory. Some late-onset neurological disorders have been reported (hypertonia, convulsion, abnormal behaviour). Whether the neurological disorders are transient or permanent is currently unknown. Any child exposed in utero to nucleoside and nucleotide analogues, even HIV-negative children should have clinical and laboratory follow-up and should be fully investigated for possible mitochondrial dysfunction in case of relevant signs or symptoms. These findings do not affect current national recommendations to use antiretroviral therapy in pregnant women to prevent vertical transmission of HIV.

Patients co-infected with hepatitis C virus.

Exacerbation of anaemia due to ribavirin has been reported when zidovudine is part of the regimen used to treat HIV although the exact mechanism remains to be elucidated. Therefore, the co-administration of ribavirin and zidovudine is not advised and consideration should be given to replacing zidovudine in a combination ART regimen if this is already established. This is particularly important in patients with a known history of zidovudine induced anaemia.

Information for patients.

In order to ensure the safe and effective use of zidovudine it is necessary that the patient should be made adequately aware of the benefits and risks associated with its use. It is recommended that the following information, in addition to any other considered appropriate by the treating clinician, should be provided to the patient. Zidovudine is not a cure for HIV infections, and patients may continue to acquire illnesses associated with HIV, including opportunistic infections. Therefore, patients should be advised to seek medical care for any significant change in their health status.
Patients should be informed that the drug has been extensively studied but for limited periods of time, and that long-term safety and efficacy are not known, particularly for patients without symptoms or with less advanced disease. Patients should be informed that the major toxicities of zidovudine are granulocytopenia and/or anaemia.
The frequency and severity of these toxicities are greater in patients with more advanced disease and those who initiate therapy later in the course of their infection. They should be told that if toxicity develops, they may require transfusions or dose modifications including possible discontinuation. They should be told of the extreme importance of having their blood counts followed regularly while on therapy and especially closely for patients with advanced symptomatic HIV disease. They should be cautioned about the use of other medications, such as paracetamol, that may exacerbate the toxicity of zidovudine (see Section 4.4 Special Warnings and Precautions for Use).
Retrovir Capsules, Tablets and Syrup are for oral ingestion only. Patients should be told of the importance of taking zidovudine exactly as prescribed. They should be told not to share medication and not to exceed the recommended dose. Patients should be told that the long-term effects of zidovudine are unknown at this time.
While effective viral suppression with antiretroviral therapy has been proven to substantially reduce the risk of sexual transmission, a residual risk cannot be excluded. Precautions to prevent transmission should be taken in accordance with national guidelines.

Use in hepatic impairment.

The use of zidovudine in patients with hepatic impairment is discussed under Dose and Method of Administration.

Use in renal impairment.

The use of zidovudine in patients with renal impairment is discussed under Dose and Method of Administration.
Zidovudine is eliminated from the body following metabolism (glucuronidation) primarily by renal excretion; only a small fraction is excreted unchanged in the urine.

Use in the elderly.

The use of zidovudine in the elderly is discussed under Dose and Method of Administration.

Paediatric use.

Safety and effectiveness in children have not been established.

Effects on laboratory tests.

No data available.

4.5 Interactions with Other Medicines and Other Forms of Interactions

As experience of drug interactions with zidovudine is limited, care should be taken when combining with other drug regimens. The interactions listed below should not be considered exhaustive but are representative of the classes of drug where caution should be exercised.
Zidovudine does not appear to affect the pharmacokinetics of atovaquone. However, pharmacokinetic data have shown that atovaquone appears to decrease the rate of metabolism of zidovudine to its glucuronide metabolite (steady state AUC of zidovudine was increased by 33% and peak plasma concentration of the glucuronide was decreased by 19%). At zidovudine dosages of 500 or 600 mg/day it would seem unlikely that a three week, concomitant course of atovaquone for the treatment of acute PCP would result in an increased incidence of adverse reactions attributable to higher plasma concentrations of zidovudine. Extra care should be taken in monitoring patients receiving prolonged atovaquone therapy.
Clarithromycin tablets reduce the absorption of zidovudine. This can be avoided by separating the administration of zidovudine and clarithromycin by at least two hours.
Co-administration of zidovudine with drugs that are nephrotoxic, cytotoxic, or which interfere with RBC/WBC number or function (e.g. pyrimethamine, sulfamethoxazole and trimethoprim, doxorubicin, dapsone, systemic pentamidine, ganciclovir, amphotericin B, flucytosine, vincristine, vinblastine, adriamycin or interferon) may increase the risk of toxicity. If concomitant therapy with any of these drugs is necessary then extra care should be taken in monitoring renal function and haematological parameters and, if required, the dosage of one or more agents should be reduced.
Zidovudine may inhibit the intracellular phosphorylation of stavudine when the two medicinal products are used concurrently. Stavudine is therefore not recommended to be used in combination with Retrovir.
Probenecid may reduce renal excretion of zidovudine and in addition, like some other drugs (e.g. codeine, methadone, morphine, inosine pranobex, paracetamol, aspirin, or indomethacin, ketoprofen, naproxen, oxazepam, lorazepam, cimetidine, clofibrate, dapsone) may alter the metabolism of zidovudine by competitively inhibiting glucuronidation or directly inhibiting hepatic microsomal metabolism (see Section 4.4 Special Warnings and Precautions for Use). Careful thought should be given to the possibilities of drug interactions before using such drugs, particularly for chronic therapy, in combination with zidovudine.
Paracetamol use during treatment with zidovudine in a placebo-controlled trial was associated with an increased incidence of neutropenia especially following chronic therapy. However, the available pharmacokinetic data indicate that paracetamol does not increase plasma levels of zidovudine nor of its glucuronide metabolite.
Phenytoin blood levels have been reported to be low in some patients receiving zidovudine, while in one case a high level was documented. These observations suggest that phenytoin levels should be carefully monitored in patients receiving zidovudine since many patients with advanced HIV infections have CNS conditions which may predispose to seizure activity.
Some experimental nucleoside analogues affecting DNA replication antagonise the in vitro antiviral activity of zidovudine against HIV and thus, concomitant use of such drugs should be avoided.
The nucleoside analogue ribavirin antagonises the in vitro antiviral activity of zidovudine and so concomitant use of this drug should be avoided.
Some drugs such as trimethoprim and sulfamethoxazole, aerosolised pentamidine, pyrimethamine and aciclovir, may be necessary for the management or prevention of opportunistic infections. In the controlled trial in patients with advanced HIV disease, increased toxicity was not detected with limited exposure to these drugs. However, there is one published report of neurotoxicity (profound lethargy) associated with concomitant use of zidovudine and aciclovir.

4.6 Fertility, Pregnancy and Lactation

Effects on fertility.

No effect on male or female fertility (judged by conception rates) was seen in rats given zidovudine orally at doses up to 225 mg/kg twice daily.
There are no data on the effect of zidovudine on human female fertility. In men zidovudine has not been shown to affect sperm count, morphology or motility.
(Category B3)
Zidovudine has been evaluated in the Antiretroviral Pregnancy Registry (APR) in over 13,000 women during pregnancy and postpartum. Available human data from the APR do not show an increased risk of major birth defects for zidovudine compared to the background rate (see Section 5.1 Pharmacodynamic Properties, Clinical trials).
The safe use of zidovudine in human pregnancy has not been established in adequate and well-controlled trials investigating congenital abnormalities. Therefore administration of zidovudine in pregnancy should be considered only if the expected benefit outweighs the possible risk to the foetus.
Zidovudine crosses the human placenta. Zidovudine has been associated with findings in animal reproductive studies. Pregnant women considering using zidovudine during pregnancy should be made aware of these findings. It is fetotoxic in animals. Oral teratology studies in the rat and in the rabbit at doses up to 250 mg/kg twice daily revealed no evidence of teratogenicity with zidovudine. The incidence of foetal resorptions was increased in rats given 75 or 225 mg/kg twice daily and rabbits given 250 mg/kg twice daily: dosages which give plasma levels of > 19.5 and 200.7 micromolar respectively at 30 minutes after dosing. A separate study, reported subsequently, has shown that 3000 mg/kg/day (as two equal doses at least 6 hours apart) given to rats during the period of organogenesis, caused marked maternal toxicity and an increased incidence of foetal malformations. This dose is comparable to the single oral median lethal dose of 3683 mg/kg in the rat. No evidence of increased incidence of foetal abnormality was observed in this study at the lower dose rates administered - 600 mg/kg/day or less, also given as 2 equal doses.
There have been reports of mild, transient elevations in serum lactate levels, which may be due to mitochondrial dysfunction, in neonates and infants exposed in utero or peri-partum to nucleoside reverse transcriptase inhibitors (NRTIs). The clinical relevance of transient elevations in serum lactate is unknown. There have also been very rare reports of developmental delay, seizures and other neurological disease. However, a causal relationship between these events and NRTI exposure in utero or peri-partum has not been established. These findings do not affect current recommendations to use antiretroviral therapy in pregnant women to prevent vertical transmission of HIV.
It is not known whether zidovudine can cause foetal harm when administered to a pregnant woman or can affect reproductive capacity. Zidovudine should be given to a pregnant woman only if clearly needed.
Excretion of zidovudine in breast milk has been reported in clinical studies, resulting in sub-therapeutic infant plasma levels.
Breast feeding is not advised because of the potential for HIV transmission from mother to child, and the potential risk of adverse events due to antiretroviral drug excretion in breast milk.
In settings where formula feeding is unsafe or unavailable, the World Health Organisation has provided guidelines.

4.7 Effects on Ability to Drive and Use Machines

There have been no studies to investigate the effect of zidovudine on driving performance or the ability to operate machinery. Further, a detrimental effect on such activities cannot be predicted from the pharmacology of the drug. Nevertheless, the clinical status of the patient and the adverse event profile of zidovudine should be borne in mind when considering the patient's ability to drive or operate machinery.

4.8 Adverse Effects (Undesirable Effects)

The frequency and severity of adverse events associated with the use of zidovudine are greater in patients with more advanced infection at the time of initiation of therapy. Tables 2, 3 and 4 summarise the relative incidence of haematologic adverse events observed in the placebo controlled clinical studies by severity of HIV disease present at the start of treatment:
The most serious adverse reactions include anaemia (which may require transfusions), neutropenia and leucopenia. These occur more frequently at higher dosages (1200-1500 mg/day) and in patients with advanced HIV disease (especially when there is poor bone marrow reserve prior to treatment), particularly in patients with CD4 cell counts less than 100/mm³. Dosage reduction or cessation of therapy may become necessary (see Section 4.2 Dose and Method of Administration). The anaemia appeared to be the result of impaired erythrocyte maturation as evidenced by increasing macrocytosis (MCV) while on the drug.
The incidence of neutropenia was also increased in those patients whose neutrophil counts, haemoglobin levels and serum vitamin B₁₂ levels were low at the start of zidovudine therapy, and in those patients taking paracetamol concurrently (see Section 4.5 Interactions with Other Medicines and Other Forms of Interactions).
Some of the HIV-infected individuals participating in these clinical trials had baseline symptoms and signs of HIV disease and/or experienced adverse events at some time during study. It was often difficult to distinguish adverse events possibly associated with zidovudine administration from underlying signs of HIV disease or intercurrent illnesses. The possibility of such events being drug related, however, cannot be excluded. Table 5 summarises clinical adverse events or symptoms which occurred in at least 5% of all patients with advanced HIV disease treated with zidovudine in the original placebo-controlled study. Of the items listed in Table 5, only severe headache, nausea, insomnia, and myalgia were reported at a significantly greater rate in zidovudine recipients.
Clinical adverse events which occurred in less than 5% of all patients treated with zidovudine in the advanced HIV study are listed below. Since many of these adverse events were seen in placebo-treated patients as well as zidovudine recipients, their possible relationship to the drug is unknown.

Body as a whole.

Body odour, chills, oedema of the lip, flu syndrome, hyperalgesia, back pain, lymphadenopathy, chest pain, generalised pain.

Cardiovascular.

Vasodilation.

Gastrointestinal.

Constipation, dysphagia, oedema of the tongue, eructation, flatulence, bleeding gums, rectal haemorrhage, mouth ulcer.

Hepatic.

Changes in liver function tests including increases in SGOT levels.

Musculoskeletal.

Arthralgia, muscle spasm, tremor, twitch, myopathy.

Nervous.

Anxiety, confusion, depression, emotional lability, nervousness, syncope, loss of mental acuity, vertigo, seizures.

Respiratory.

Cough, epistaxis, pharyngitis, rhinitis, sinusitis, hoarseness.

Skin.

Acne, pruritus, urticaria, nail pigmentation.

Special senses.

Amblyopia, hearing loss, photophobia.

Urogenital.

Dysuria, polyuria, urinary frequency, urinary hesitancy.
Subsequent to the initial trial, sensitisation reactions, including anaphylaxis in one patient, have been reported in individuals receiving zidovudine therapy.
All unexpected events and expected events of a severe or life-threatening nature were monitored in the placebo-controlled studies in early HIV disease and asymptomatic HIV infection. Data concerning the occurrence of additional signs or symptoms were also collected. No distinction was made in reporting events between those possibly associated with the administration of the study medication and those due to the underlying disease. Tables 6 and 7 summarise all those events reported at a statistically significant greater incidence for zidovudine recipients in these studies:

The following events have also been reported in patients treated with zidovudine. They may occur as part of the underlying disease process or as a result of the wide range of drugs used in the management of HIV disease. The relationship between these events and the use of zidovudine is therefore difficult to evaluate, particularly in the medically complicated situations which characterise advanced HIV disease. If the severity of the symptoms warrants it, a reduction or suspension of zidovudine therapy may assist in the assessment and management of these conditions:
cardiomyopathy;
pancytopenia with marrow hypoplasia and isolated thrombocytopenia;
lactic acidosis in the absence of hypoxaemia;
liver disorders, such as severe hepatomegaly with steatosis, raised blood levels of liver enzymes and bilirubin;
pancreatitis;
skin and oral mucosa pigmentation;
red cell aplasia and aplastic anaemia.

Adverse reactions with combination therapy.

Information regarding the safety of zidovudine in combination with other antiretroviral drugs is limited. Physicians should refer to the complete product information for the respective antiretroviral therapy for a description of the known associated adverse reactions.
Only limited safety data are available on the combined use of zidovudine with zalcitabine. Clinical adverse events occurring in > 3% of patients treated with zalcitabine 0.005 and 0.01 mg/kg every eight hours administered concomitantly with zidovudine 100 mg or 200 mg every eight hours, as well as zidovudine 50 mg every eight hours alone or combined with zalcitabine 0.005 mg/kg every eight hours, are listed in Table 8. One patient with advanced HIV disease died of refractory acidosis, mild pancreatitis, hepatomegaly with steatosis, and an unexplained neurological syndrome. The investigator assessed this event as remotely related to zidovudine and/or the combination of zidovudine and zalcitabine.

Treatment with zidovudine has been associated with loss of subcutaneous fat (see Section 4.4 Special Warnings and Precautions for Use).

Post marketing data.

Metabolism and nutrition disorders.

Hyperlactataemia (common), lactic acidosis (rare, see Section 4.4 Special Warnings and Precautions for Use).

Reporting suspected adverse effects.

Reporting suspected adverse reactions after registration of the medicinal product is important. It allows continued monitoring of the benefit-risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions at http://www.tga.gov.au/reporting-problems.

4.9 Overdose

No specific symptoms or signs have been identified following acute overdose with zidovudine, apart from those listed as undesirable effects.

Treatment.

Patients should be observed closely for evidence of toxicity (see Section 4.8 Adverse Effects (Undesirable Effects)) and given the necessary supportive therapy.
Haemodialysis and peritoneal dialysis appear to have a negligible effect on the removal of zidovudine. The primary metabolite, GAZT, appears to be more efficiently removed by haemodialysis than peritoneal dialysis.
For information on the management of overdose, contact the Poison Information Centre on 131126 (Australia).

5 Pharmacological Properties

5.1 Pharmacodynamic Properties

Retrovir is the brand name for zidovudine (formerly called azidothymidine (AZT)), an antiretroviral drug active against human immunodeficiency virus (HIV).

Mechanism of action.

Zidovudine is an inhibitor of the in vitro replication of some retroviruses including HIV (also known as HTLV III, LAV or ARV). This drug is a thymidine analogue in which the 3'-hydroxy (-OH) group is replaced by an azido (-N₃) group. Cellular thymidine kinase converts zidovudine into zidovudine monophosphate. The monophosphate is further converted into the diphosphate by cellular thymidylate kinase and to the triphosphate derivative by other cellular enzymes. Zidovudine triphosphate interferes with the HIV viral RNA dependent DNA polymerase (reverse transcriptase) and thus inhibits viral replication. Zidovudine triphosphate also inhibits cellular α-DNA polymerase, but at concentrations 100-fold higher than those required to inhibit reverse transcriptase. In vitro, zidovudine triphosphate has been shown to be incorporated into growing chains of DNA by viral reverse transcriptase. When incorporation by the viral enzyme occurs, the DNA chain is terminated. Studies in cell culture suggest that zidovudine incorporation by cellular α-DNA polymerase may occur, but only to a very small extent and not in all test systems. Chain termination has not been demonstrated with cellular α-DNA polymerase.

Microbiology.

The relationship between in vitro susceptibility of HIV to zidovudine and the inhibition of HIV replication in man or clinical response to therapy has not been established. In vitro sensitivity results vary greatly depending upon the time between virus infection and zidovudine treatment, the particular assay used, the cell type employed and the laboratory performing the test. In addition, the methods currently used to establish virologic responses in clinical trials may be relatively insensitive in detecting changes in the quantities of actively replicating HIV or reactivation of these viruses. Zidovudine blocked 90% of detectable HIV replication in vitro at concentrations of < 0.13 microgram/mL (ID₉₀) when added shortly after laboratory infection of susceptible cells. This level of antiviral effect was observed in experiments measuring reverse transcriptase activity in H9 cells, PHA stimulated peripheral blood lymphocytes, and unstimulated peripheral blood lymphocytes. The concentration of drug required to produce a 50% decrease in supernatant reverse transcriptase was 0.013 microgram/mL (ID₅₀) in both H9 cells and peripheral blood lymphocytes. Zidovudine at concentrations of 0.13 microgram/mL also provided > 90% protection from a strain of HIV (HTLV IIIB) induced cytopathic effects in two tetanus-specific T4 cell lines. p24 gag protein expression was also undetectable at the same concentration in these cells. Partial inhibition of viral activity in cells with chronic HIV infection (presumed to carry integrated HIV DNA) required concentrations of zidovudine (8.8 microgram/mL in one laboratory to 13.3 microgram/mL in another) which are approximately 100 times as high as those necessary to block HIV replication in acutely infected cells. There are limited data on the development of resistance to zidovudine.
Reduced in vitro sensitivity to zidovudine has been reported for HIV isolates from patients who have received prolonged courses of zidovudine therapy. The available information indicates that for early HIV disease, the frequency and degree of reduction of in vitro sensitivity is notably less than for advanced disease.
The major metabolite of zidovudine, 3'-azido- 3'-deoxy- 5'-O-β-D-glycopyranuronosylthymidine (GAZT), does not inhibit HIV replication in vitro. GAZT does not antagonise the antiviral effect of zidovudine in vitro nor does GAZT compete with zidovudine triphosphate as an inhibitor of HIV reverse transcriptase.
The cytotoxicity of zidovudine for various cell lines was determined using a cell growth assay. ID₅₀ values for several human cell lines showed little growth inhibition by zidovudine except at concentrations > 50 microgram/mL. However, one human T-lymphocyte cell line was sensitive to the cytotoxic effect of zidovudine with an ID₅₀ of 5 microgram/mL. Moreover, in a colony-forming unit assay designed to assess the toxicity of zidovudine for human bone marrow, an ID₅₀ value of < 1.25 microgram/mL was estimated. Two of ten human lymphocyte cultures tested were found to be sensitive to zidovudine at 5 microgram/mL or less.
Zidovudine has antiviral activity against some other mammalian retroviruses in addition to HIV. No significant inhibitory activity was exhibited against a variety of other human and animal viruses, except an ID₅₀ of 1.4 to 2.7 microgram/mL against the Epstein-Barr virus, the clinical significance of which is not known at this time.
No antagonistic effects in vitro were seen with zidovudine and other antiretrovirals (tested agents: abacavir, didanosine, lamivudine and interferon-alpha).
There is currently no evidence that zidovudine plus zalcitabine prevents the emergence of zidovudine-resistant isolates. However, in vitro studies with zidovudine-resistant virus isolates indicate such strains remain sensitive to zalcitabine.

Clinical trials.

Monotherapy.

Advanced HIV disease.

A randomized, double-blind, placebo-controlled trial (BW 02) of oral zidovudine (1500 mg/day) was conducted in 281 adults with advanced HIV disease which included 160 patients with AIDS and 121 patients with ARC.
There were 19 deaths (12 in patients with AIDS, 7 in patients with ARC) in the placebo group and 1 death (patient with AIDS) in the group receiving zidovudine. Treatment with zidovudine significantly improved the probability of survival for 24 weeks in both the AIDS and ARC subgroups. During a follow-up protocol with open-label treatment with zidovudine, patients who were initially randomized to receive zidovudine continued to have better overall survival than did patients initially randomized to placebo. Survival rates in the group of patients originally randomized to receive zidovudine declined to 85% after 1 year, 41% after 2 years, and 23% after 3 years. These survival rates may be lower than currently observed due to the absence of opportunistic infection prophylaxis in this study. Zidovudine also significantly reduced the risk of acquiring an AIDS-defining opportunistic infection, and patients who received zidovudine generally did better than the placebo group in terms of several other measures of efficacy, including performance level, neuropsychiatric function, maintenance of body weight, and the number and severity of symptoms associated with HIV disease.
The weight of evidence indicates an overall beneficial effect of zidovudine on HIV-associated neurological disorders. However, the effectiveness of dosages less than 1000 mg/day in the treatment or prevention of HIV-associated neurological dysfunction is unknown.

Asymptomatic HIV infection and early HIV disease (CD4 between 200 to 500 cells/mm³).

The population indicated for monotherapy with zidovudine was extended to asymptomatic or symptomatic adults with CD4 cell counts of 500 cells/mm³ or less, based on the results of two randomized double-blind placebo-controlled trials (ACTG 019, ACTG 016) of 2051 adults. Treatment with zidovudine reduced the risk of progression to advanced HIV disease (ARC, AIDS or death) and significantly improved the CD4 cell count. Survival benefit could not be assessed due to the limited duration of follow-up at the time the placebo arms were discontinued. Other large studies of longer duration have not shown additional survival benefit of early versus delayed therapy with zidovudine above that seen for patients with advanced HIV disease.
Combination therapy.

Combination therapy of zidovudine with zalcitabine or didanosine.

A randomised, double-blind trial (ACTG 175) compared combinations of zidovudine (200 mg tds) plus didanosine (200 mg bd) or zalcitabine (0.75 mg tds) with zidovudine alone or didanosine alone. The trial was conducted in 2567 HIV-infected adults without AIDS and with CD4 cell counts ≥ 200 and ≤ 500 cells/mm³ (mean 352 cells/mm³), of whom 1067 were antiretroviral naive and 1400 had received more than 1 week of prior therapy (median > 18 months). Median duration of follow-up was 143 weeks.
Compared to zidovudine alone, zidovudine plus didanosine was associated with a significant reduction in combined study endpoint (decline in CD4 count, progression to an AIDS defining event or death) of 50% (p < 0.001) and the zidovudine plus zalcitabine combination was associated with a reduction of 46% (p < 0.001) in the combined study endpoint. In the overall trial (combined data for antiretroviral naive and antiretroviral experienced patients), statistically significant benefit of both of the two combinations was shown compared to zidovudine alone for the combined study endpoint.
Compared to zidovudine alone, zidovudine plus didanosine was associated with a significant reduction in combined clinical endpoint (progression to an AIDS defining event or death) of 35% (p = 0.025) for antiretroviral experienced patients and 36% (p = 0.005) for the overall trial. Compared to zidovudine monotherapy, zidovudine plus zalcitabine was associated with a significant reduction of 51% (p = 0.016) in the combined clinical endpoint for antiretroviral naive patients.
Compared to zidovudine monotherapy, zidovudine plus didanosine showed a significant reduction in mortality of 48% (p = 0.019) for antiretroviral experienced patients and of 45% (p = 0.008) for the overall trial.
A randomised, double-blind trial (Delta) compared the combination of zidovudine (200 mg tds) plus didanosine (200 mg bd) or zalcitabine (0.75 mg tds) with zidovudine alone. The trial was conducted in 3207 HIV-infected adults, with CD4 cell counts ≥ 50 and ≤ 350 cells/mm³ (mean 205 cells/mm³). 2124 participants were zidovudine naive (Delta 1) and 1083 participants had at least 3 months prior zidovudine (Delta 2). The median duration of follow-up was 30 months.
In the overall trial, in comparison to zidovudine alone, zidovudine plus didanosine was associated with a reduction in mortality of 33% (p < 0.0001) and zidovudine plus zalcitabine was associated with a reduction in mortality of 21% (p = 0.008). In Delta 1, evidence of a survival benefit was strong in the combination treatment groups compared to zidovudine alone (overall p < 0.0001). In Delta 2, there was less evidence of a difference in mortality between combination treatment groups compared to zidovudine alone (p = 0.19). Overall there was a delay in disease progression, with benefit seen mainly in participants who had not received zidovudine before.

Combination therapy of zidovudine with 3TC (lamivudine) or zalcitabine.

Four double-blind, multicentre studies have been conducted in HIV-infected adults with (NUCA3001 and NUCB3001) or without (NUCA3002 and NUCB3002) prior antiretroviral therapy (see Table 9). After 24 weeks, in zidovudine naive patients, the combination of zidovudine and lamivudine resulted in a significant increase in absolute CD4 count and reduction on log₁₀ HIV RNA relative to zidovudine monotherapy or lamivudine monotherapy. In zidovudine experienced patients, the combination of zidovudine and lamivudine resulted in significantly greater improvements in CD4 cell count than either zidovudine monotherapy or the combination of zidovudine and zalcitabine and a significantly greater reduction in log₁₀ HIV RNA than zidovudine monotherapy. In the zidovudine experienced groups, analysis of a subset of patients receiving treatment for at least 52 weeks established that the benefit of combined zidovudine and lamivudine treatment on CD4 cell count and viral load was maintained compared to zidovudine monotherapy.

Clinical end-point data from a prospective study indicate that lamivudine in combination with zidovudine alone or in combination with zidovudine containing treatment regimens results in a significant reduction in the risk of disease progression and mortality.
NUCB3007 (CAESAR) was a multicenter, double-blind, placebo-controlled study comparing continued current therapy [zidovudine (AZT) alone (62% of patients) or zidovudine with didanosine (ddI) or zalcitabine (ddC) (38% of patients)] to the addition of 3TC or 3TC plus an investigational non-nucleoside reverse transcriptase inhibitor, randomised 1:2:1. A total of 1,840 HIV-infected adults with 25 to 250 (median, 126) CD4 cells/mm³ at baseline were enrolled: median age was 36 years, 87% were male, 83% were nucleoside-experienced, and 17% were therapy-naive. The median duration of treatment for each group was current therapy* 327 days, 3TC plus current therapy* 360 days and 3TC plus NNRTI** plus current therapy* 360 days. Results are summarised in Table 10.

The data showed there was a significant reduction in progression to the combined endpoint of a new AIDS event or death for patients who received lamivudine in combination with zidovudine containing regimens compared to patients maintained on zidovudine containing regimens alone (p < 0.0001). The Hazard Ratio (HR) was 0.427 (95% confidence interval 0.318-0.572), or a 57% reduction in risk. In addition, the data indicated a significant reduction in death, regardless of causality, in the combination lamivudine plus zidovudine containing regimens as compared to the zidovudine containing regimens alone (p = 0.0007); HR = 0.399 (95% CI 0.230-0.693) or a 60% reduction in risk.
ACTG320 was a randomised, double-blind, placebo-controlled study to compare indinavir, zidovudine (or stavudine) and lamivudine with the 2 drug regimen of zidovudine (or stavudine) and lamivudine in HIV-infected patients with CD4 counts ≤ 200 cells/mm³. Patients had received ≥ 3 months prior zidovudine therapy and had no prior exposure to protease inhibitors. A total of 1156 patients were randomized. The median duration of follow-up was 38 weeks. During the study there were 96 new AIDS-defining events or deaths, 63 (11%) in the zidovudine/lamivudine arm and 33 (6%) in the zidovudine/lamivudine/indinavir arm (estimated Hazard Ratio 0.50). There were 13 (6%) deaths in the zidovudine/lamivudine arm and 5 (2%) in the zidovudine/lamivudine/indinavir arm (Hazard Ratio 0.37). Both these results were statistically significant.
Pregnancy. The Antiretroviral Pregnancy Registry (APR) has received reports of over 13,000 exposures to zidovudine during pregnancy resulting in live birth. These consist of over 4,100 exposures during the first trimester, over 9,300 exposures during the second/third trimester and included 133 and 264 birth defects respectively. The prevalence (95% CI) of defects in the first trimester was 3.2% (2.7, 3.8%) and in the second/third trimester, 2.8% (2.5, 3.2%). This proportion is not significantly higher than those reported in the two population based surveillance systems (2.72 per 100 live births and 4.17 per 100 live births respectively). The APR does not show an increased risk of major birth defects zidovudine compared to the background rate.

5.2 Pharmacokinetic Properties

Absorption.

After oral dosing, zidovudine was rapidly absorbed from the gastrointestinal tract with peak serum concentrations occurring within 0.5 to 1.5 hours. Kinetics appeared to be dose-independent over the range of 2 mg/kg every 8 hours to 10 mg/kg every 4 hours. The mean zidovudine half-life was approximately 1 hour and ranged from 0.78 to 1.93 hours following oral dosing. When zidovudine capsules are taken with food there is an increase in the time to achieve maximum plasma concentration and a reduction in maximum plasma concentration. There is a small and variable effect on overall exposure to zidovudine, as estimated by AUC. The clinical significance of these changes is not known. The effect of food on absorption of zidovudine syrup is not known.
Steady-state serum concentrations of zidovudine following chronic oral administration of 250 mg every 4 hours (3.0 to 5.4 mg/kg) were determined in 21 patients (body weight ranged from 46.0 to 83.6 kg) in a Phase II trial. Mean steady-state predose and 1.5 hours postdose zidovudine concentrations were 0.16 microgram/mL (range 0 to 0.84 microgram/mL) and 0.62 microgram/mL (range 0.05 to 1.46 microgram/mL), respectively.

Distribution.

In adults, the average cerebrospinal fluid/plasma zidovudine concentration ratio 2-4 hours after dosing was found to be approximately 0.5. Limited data indicate that zidovudine crosses the placenta and is found in amniotic fluid and foetal blood. Zidovudine has also been detected in semen.

Metabolism.

Zidovudine is rapidly metabolised during first pass to 3'-azido-3'-deoxy-5'-O-β-D-glucopyranuronosylthymidine (GAZT) which has an apparent elimination half-life of 1 hour (range 0.61 to 1.73 hours). This reduces the bioavailability from the capsule formulation. Based on limited data the average oral capsule bioavailability appears to be 65% (range 52-75%). Following oral administration, urinary recoveries of zidovudine and GAZT accounted for 14 and 74% of the dose, respectively, and the total urinary recovery averaged 90% (range 63 to 95%), indicating a high degree of absorption.
Limited data has identified 3'-amino-3'deoxythymidine (AMT) as a metabolite of zidovudine following intravenous and oral dosing. A small in vitro study showed that AMT reduced the growth of haemopoietic progenitor cells; the clinical significance of this finding is unknown.
In a multiple dose bioavailability study conducted in 12 HIV-infected adults receiving doses of 100 mg or 200 mg every four hours, two formulations of zidovudine oral solution, one of which differed only slightly from the marketed formulation, were demonstrated to be bioequivalent to zidovudine capsules with respect to area under the concentration-time curve (AUC). The rate of absorption of zidovudine solution was greater than that of zidovudine capsules, as indicated by mean times to peak concentration of 0.5 and 0.8 hours, respectively. Mean values for steady-state peak concentration (dose-normalised to 200 mg) were 1.5 and 1.2 mg/mL for solution and capsules, respectively.

Excretion.

Renal clearance is estimated to be 400 mL/min/70 kg, indicating glomerular filtration and active tubular secretion by the kidneys. Zidovudine plasma protein binding is 34 to 38%. The zidovudine cerebrospinal fluid (CSF) concentration measured 1.8 hours following oral dosing at 2 mg/kg was 0.04 microgram/mL (n = 1).
There are limited data on the pharmacokinetics of zidovudine in patients with renal or hepatic impairment (see Section 4.2 Dose and Method of Administration). There are also limited data on the pharmacokinetics of zidovudine in pregnant women. No specific data are available on the pharmacokinetics of zidovudine in the elderly.

5.3 Preclinical Safety Data

Genotoxicity.

No evidence of mutagenicity (with or without metabolic activation) was observed in the Ames Salmonella mutagenicity assay. In a mutagenicity assay conducted in L5178Y/TK+/- mouse lymphoma cells, zidovudine was weakly mutagenic in the absence of metabolic activation only at the highest concentrations tested (4000 and 5000 microgram/mL).
In the presence of metabolic activation, the drug was weakly mutagenic at concentrations of 1000 microgram/mL and higher. In an in vitro cytogenetic study performed in cultured human lymphocytes, zidovudine induced dose-related structural chromosomal abnormalities at concentrations of 3 microgram/mL and higher. No such effects were noted at the two lowest concentrations tested, 0.3 and 1 microgram/mL.
Zidovudine was clastogenic in an in vivo micronucleus test after multiple oral doses > 100 mg/kg/day in mice and 500 mg/kg/day in rats. Zidovudine was not clastogenic in rats after single IV dosages of 37.5 to 300 mg/kg.
A study of the peripheral blood lymphocytes of eleven AIDS patients showed a higher chromosome breakage frequency in those who had received zidovudine than in those who had not. The clinical significance of these findings is unclear.

Carcinogenicity.

Zidovudine was administered orally at three dosage levels to separate groups of mice and rats (60 females and 60 males in each group). Initial single daily doses were 30, 60 and 120 mg/kg/day in mice and 80, 220 and 600 mg/kg/day in rats. The doses in mice were reduced to 20, 30 and 40 mg/kg/day after day 90 because of treatment-related anaemia, whereas in rats only the high dose was reduced to 450 mg/kg/day on day 91 and then to 300 mg/kg/day on day 279.
In mice, seven late-appearing (after 19 months) vaginal neoplasms (5 squamous cell carcinomas, one squamous cell papilloma and one squamous polyp) occurred in animals given the highest dose. One late-appearing squamous cell papilloma occurred in the vagina of a middle dose animal. No vaginal tumours were found at the lowest dose. In rats, two late-appearing (after 20 months) vaginal squamous cell carcinomas occurred in animals given the highest dose. No vaginal tumours occurred at the low or middle dose in rats.
No other drug-related tumours were observed in either sex of either species.
It is not known how predictive the results of rodent carcinogenicity studies may be for man. At the highest doses tested at which no tumours were reported the estimated drug exposure (as measured by AUC values) was more than 2 times (mouse) and more than 20 times (rat) the estimated human exposure at the recommended therapeutic dose of 500 mg/day.

6 Pharmaceutical Particulars

6.1 List of Excipients

Retrovir Capsules 100 mg.

Each capsule contains starch-maize, cellulose microcrystalline, sodium starch glycollate, magnesium stearate, gelatin, titanium dioxide and TekPrint SW-9008 Black ink or Opacode S-1-277002 Black.

Retrovir Capsules 250 mg.

Each capsule contains starch-maize, cellulose microcrystalline, sodium starch glycollate, magnesium stearate, gelatin, titanium dioxide, indigo carmine and TekPrint SW-9008 Black ink or Opacode S-1-277002 Black.

Retrovir Syrup.

Each 5 mL contains glycerol, citric acid, sodium benzoate, saccharin sodium, maltitol solution, Flavour Strawberry PHL-134189, Flavour White Sugar DA13780, and water-purified.

6.2 Incompatibilities

Incompatibilities were either not assessed or not identified as part of the registration of this medicine.

6.3 Shelf Life

In Australia, information on the shelf life can be found on the public summary of the ARTG. The expiry date can be found on the packaging.

6.4 Special Precautions for Storage

Store below 30°C. Protect from light.

6.5 Nature and Contents of Container

Retrovir Capsules 100 mg.

Bottles or blister packs of 100.

Retrovir Capsules 250 mg.

Blister packs of 40 or 60.

Retrovir Syrup.

Bottles of 200 mL with tamper-evident caps. Syringe, syringe adaptor and plastic cap supplied for use opening.
Not all strengths, dose forms, pack sizes, container types may be distributed in Australia.

6.6 Special Precautions for Disposal

In Australia, any unused medicine or waste material should be disposed of by taking to your local pharmacy.

6.7 Physicochemical Properties

The chemical name of zidovudine is 3'-azido-3'-deoxythymidine. Zidovudine has a molecular weight of 267.24 and the molecular formula C₁₀H₁₃N₅O₄.

Chemical structure.

CAS number.

30516-87-1.

7 Medicine Schedule (Poisons Standard)

S4.

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Retrovir

Zidovudine

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BRAND INFORMATION

Retrovir Capsules 100 mg

Retrovir Capsules 250 mg