Consumer medicine information

Minipress Tablets

Prazosin

BRAND INFORMATION

Brand name

Minipress

Active ingredient

Prazosin

Schedule

S4

 

Consumer medicine information (CMI) leaflet

Please read this leaflet carefully before you start using Minipress Tablets.

SUMMARY CMI

Minipress®

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 using Minipress?

Minipress contains the active ingredient prazosin. Minipress is used to treat high blood pressure, also called hypertension, benign prostatic hyperplasia or BPH ('prostrate trouble') in men waiting for prostate surgery, Raynaud's disease where the fingers become white and painful when cold, and certain types of heart failure.

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

2. What should I know before I use Minipress?

Do not take if you have ever had an allergic reaction to Minipress 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 use Minipress? in the full CMI.

3. What if I am taking other medicines?

Some medicines may interfere with Minipress 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 Minipress?

  • Start with a low dose of 0.5 mg (half a 1 mg tablet) taken twice a day.

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

5. What should I know while using Minipress?

Things you should do
  • Remind any doctor or dentist you visit that you are using Minipress.
  • If you experience continued dizziness, lightheadedness, painful erections, or become pregnant, tell your doctor immediately.
  • Take care during exercise or hot weather or if you have to stand for a long time.
Things you should not do
  • Do not stop taking this medicine or lower the dosage, without checking with your doctor.
Driving or using machines
  • Be careful driving or operating machinery until you know how Minipress affects you.
Drinking alcohol
  • Be careful to limit the amount of alcohol you drink while taking Minipress.
Looking after your medicine
  • Keep your tablets in a cool, dry place where the temperature stays below 30C.

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

6. Are there any side effects?

Side effects include feeling sick, vomiting or dry mouth, constipation, diarrhoea, weakness or lack of energy, headache or drowsiness and stuffy nose. Serious side effects include fast or pounding heartbeat, chest pain, fainting, dizziness or lightheadedness when standing up, shortness of breath or difficulty breathing, blurred vision, rash, itching or other skin problems, sharp pain in the stomach or back, persistent painful erection of the penis which occurs without sexual arousal, tingling or numbness of the hands or feet, swelling of the hands, feet or ankles and feelings of nervousness or depression.

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

Minipress® (min-e-press)

Active ingredient(s): prazosin (praz-o-sin)


Consumer Medicine Information (CMI)

This leaflet provides important information about using Minipress. 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 Minipress.

Where to find information in this leaflet:

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

1. Why am I using Minipress?

Minipress contains the active ingredient prazosin. Minipress belongs to a family of medicines called alpha blockers. These medicines work by relaxing muscles in the walls of blood vessels and reducing the resistance to blood flow. They also relieve prostate problems by relaxing muscles in the prostate gland and increasing the flow of urine.

Minipress is used to treat high blood pressure, also called hypertension, benign prostatic hyperplasia or BPH ('prostrate trouble') in men waiting for prostate surgery, Raynaud's disease, where the fingers become white and painful when cold, and certain types of heart failure.

When used to treat high blood pressure or heart failure, Minipress is often used in combination with other medicines.

Ask your doctor if you have any questions about why Minipress has been prescribed for you.

Your doctor may have prescribed it for another reason.

2. What should I know before I use Minipress?

Do not take Minipress if:

  1. you are allergic to prazosin, or any of the ingredients listed at the end of this leaflet.
  • Symptoms of an allergic reaction may include:
    - shortness of breath
    - wheezing or difficulty breathing
    - swelling of the face, lips, tongue or other parts of the body
    - rash, itching or hives on the skin.
    - always check the ingredients to make sure you can use this medicine.
  1. any other alpha blocker medicine (e.g. Hytrin).
  2. You are under 12 years of age. Minipress is not recommended for use in children under 12 years of age.

If you are not sure whether you should be taking Minipress, talk to your doctor or pharmacist.

Check with your doctor if you:

  • have allergies to:
    - any other medicines, foods, preservatives or dyes.
  • Have any other medical conditions including:
    - heart problems such as heart failure or angina
    - kidney or liver problems.
  • Take any medicines for any other condition.

If you have not told your doctor about any of the above, tell them before you start Minipress.

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

Check with your doctor if you are pregnant or intend to become pregnant.

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

If you have not told your doctor about any of the above, tell them before you start Minipress.

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.

In particular, tell your doctor if you are taking:

  • medicines used to lower blood pressure
  • fluid tablets (diuretics)
  • medicines to treat impotence (erectile dysfunction).

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

Other medicines that lower high blood pressure may have an additive effect with Minipress and make your blood pressure too low. As a result, their dose may need to be changed when Minipress is started.

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

Your doctor or pharmacist has a complete list of medicines to be careful with or avoid while taking Minipress.

4. How do I use Minipress?

How much to take

  • Minipress is usually started at a low dose of 0.5 mg (half a 1 mg tablet) taken twice a day.
  • Follow the instructions provided and use Minipress until your doctor tells you to stop.

Starting with a low dose reduces the risk of too great a drop in your blood pressure which can make you dizzy, lightheaded or faint.

Your doctor may gradually increase this dose as required. This may depend on your age, your condition and whether or not you are taking any other medicines.

Hypertension (high blood pressure)

The usual starting dose is 0.5 mg (half a 1 mg tablet) taken twice a day increasing to 1 mg taken two or three times a day. Your doctor may increase this up to 20 mg a day, taken in divided doses.

Heart failure

The usual starting dose is 0.5 mg (half a 1 mg tablet) increasing to 4 mg a day, divided into three or four doses. This may be increased by your doctor up to 20 mg a day, taken in divided doses.

Raynaud's disease

The usual starting dose is 0.5 mg (half a 1 mg tablet) taken twice a day. Your doctor may increase this up to 1 mg or 2 mg taken twice a day.

Benign prostatic hyperplasia (BPH)

The usual starting dose is 0.5 mg (half a 1 mg tablet) taken twice a day. Your doctor may increase this to 2 mg taken twice a day.

When to take Minipress

  • Minipress should be taken at the same time each day.

When you first start taking Minipress or if your doctor increases your dose, take the first dose last thing at night, just before going to bed.

Be especially careful if you need to get up during the night, because you may feel dizzy and could fall.

How to take Minipress

  • Swallow the tablets with a glass of water or other liquid.
  • It does not matter if you take Minipress before or after food.

How long to take Minipress

Keep taking Minipress every day until your doctor tells you to stop.

If you are taking Minipress for high blood pressure, heart failure or Raynaud's disease, you may need to take it for a long time.

Minipress will help control these conditions, but will not cure them. Therefore, it must be taken every day.

If you are taking Minipress for prostate problems, you will only have to take it until your operation.

If you forget to use Minipress

Minipress should be used regularly at the same time each day. If you miss your dose at the usual time, and it is within 3 hours before your next dose, skip the dose you missed and take the 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 are not sure what to do, check with your doctor or pharmacist.

If you miss two (2) doses or more, you will need to restart at a low dose and build up again gradually to your usual dose.

  • Ask your doctor how to do this.

If you take too much Minipress

If you take too much Minipress, you may feel lightheaded, dizzy, have a fast or irregular heartbeat, or you may faint.

If you think that you, a child or anyone else may have taken too much Minipress, 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 Minipress?

Things you should do

Get up slowly after you have been sitting or lying down.

Minipress can cause dizziness, lightheadedness and fainting, particularly if you get up too quickly. This is also more likely to occur if you have just started Minipress or the dose of Minipress has just been increased.

These symptoms can be dangerous, particularly if you are 65 years or older and have heart disease.

If you feel dizzy or lightheaded, lie down so that you do not faint. Then sit for a few moments before standing to prevent the dizziness from returning.

If these symptoms continue, tell your doctor.

A change in dose may be needed.

Call your doctor straight away if you:

  • experience painful erections or if your erection continues for longer than four hours.
  • become pregnant while taking Minipress
  • are about to start any new medicines, tell your doctor that you are taking Minipress.

Remind any doctor or dentist you visit that you are using Minipress.

Things you should not do

  • Do not give Minipress to anyone else, even if they have the same condition as you.
  • Do not use Minipress to treat any other complaints unless your doctor tells you to.
  • Do not stop taking Minipress, or lower the dosage, without checking with your doctor.

Your doctor will reduce your dose of Minipress gradually if you are to stop taking this medicine.

Driving or using machines

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

Minipress may cause dizziness, lightheadedness or fainting in some people, especially after the first dose or after a dose increase. Blurred vision or drowsiness may also occur.

Make sure you know how you react to Minipress before you drive a car, operate machinery or do anything else that could be dangerous if you are dizzy, drowsy, or are not alert.

Drinking alcohol

Tell your doctor if you drink alcohol.

Be careful to limit the amount of alcohol you drink while taking Minipress. Also, take extra care during exercise or hot weather or if you have to stand for a long time.

Dizziness, lightheadedness, or fainting is more likely to occur if you drink alcohol, stand for a long time, exercise or the weather is hot.

Looking after your medicine

  • Keep your tablets in their pack until it is time to take them.
  • Keep them in a cool, dry place where the temperature stays below 30°C.

Follow the instructions in the carton on how to take care of your medicine properly.

Store it in a cool dry place 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.

Do not use this medicine after the expiry date.

Keep it where young children cannot reach it.

When to discard your medicine

If your doctor tells you to stop taking Minipress, or the tablets have passed their expiry date.

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.

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.

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

Side effects

If you are 65 years or older, you should be especially careful while taking Minipress. Report any side effects promptly to your doctor.

Side effectsWhat to do
  • feeling sick, vomiting or dry mouth.
  • constipation, diarrhoea
  • weakness or lack of energy
  • headache or drowsiness
  • stuffy nose
Speak to your doctor if you have any of these side effects and they worry you.
These side effects are usually mild.

Serious side effects

Serious side effectsWhat to do
  • fast or pounding heartbeat, chest pain,
  • fainting, dizziness or lightheadedness when standing up
  • shortness of breath or difficulty breathing
  • blurred vision
  • rash, itching or other skin problems
  • sharp pain in the stomach or back
  • persistent painful erection of the penis which occurs without sexual arousal
  • tingling or numbness of the hands or feet
  • swelling of the hands, feet or ankles
  • feelings of nervousness or depression.
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 Minipress contains

Active ingredient
(main ingredient)
1 mg, 2 mg or 5 mg of prazosin
Other ingredients
(inactive ingredients)
maize starch
microcrystalline cellulose
magnesium stearate
sodium lauryl sulfate
calcium hydrogen phosphate
sunset yellow FCF (1 mg tablet only).

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

This medicine does not contain lactose, or sucrose.

What Minipress looks like

1mg - orange, capsule-shaped tablets marked MNP 1 on one side and scored on the other (AUST R 10756)

2mg - white, round tablets marked MNP 2 on the scored side and plain on the other (AUST R 10757)

5mg - white, diamond shaped tablets scored on both sides, marked MNP 5 on one side (AUST R 10758)

Each box contains 100 tablets.

Who distributes Minipress

Pfizer Australia Pty Ltd
Sydney, NSW
Toll Free Number: 1800 675 229
www.pfizermedinfo.com.au

This leaflet was prepared in February 2022.

® Registered Trademark

© Pfizer Australia Pty Ltd 2022

Published by MIMS April 2022

BRAND INFORMATION

Brand name

Minipress

Active ingredient

Prazosin

Schedule

S4

 

1 Name of Medicine

Prazosin hydrochloride.

2 Qualitative and Quantitative Composition

Prazosin hydrochloride equivalent to 1 mg, 2 mg and 5 mg prazosin base.

3 Pharmaceutical Form

Tablet.
Minipress 1 mg tablets: orange, capsule-shaped with MNP 1 on one side and scored on the other.
Minipress 2 mg tablets: white, round, scored, marked with MNP 2 on the scored side.
Minipress 5 mg tablets: white, diamond-shaped, scored on both sides, marked with MNP 5 on one side.

4 Clinical Particulars

4.1 Therapeutic Indications

In patients with hypertension.

Minipress (prazosin hydrochloride) is indicated in the treatment of hypertension of varied aetiology and all grades of severity. It can be used as the initial and sole agent or it may be employed in a treatment programme in conjunction with other antihypertensive agents.
Renal blood flow and glomerular filtration rate are not impaired by long-term oral administration. Minipress can be used with safety in hypertensive patients with impaired renal function.

In patients with congestive heart failure.

Minipress is indicated in the treatment of severe refractory congestive heart failure. Minipress may be added to the therapeutic regime in those patients who have become refractory to conventional therapy with cardiac glycosides and diuretics.

In patients with Raynaud's phenomenon and Raynaud's disease.

Minipress is indicated in the treatment of Raynaud's phenomenon and Raynaud's disease.

Benign prostatic hyperplasia.

Minipress is indicated as an adjunct in the symptomatic treatment of urinary obstruction caused by benign prostatic hyperplasia in patients awaiting prostatic surgery.

4.2 Dose and Method of Administration

General comments.

There is evidence that patient toleration is best when therapy is initiated with a low starting dose. The dose is to be adjusted on the basis of the patient's individual blood pressure response.
Response is usually seen early (1 to 14 days) if it is to occur at a given dose. If a response is seen, therapy should be continued at the dose until the degree of response has reached the optimum possible before adding the next increment.

Specific recommendations.

Hypertension.

Suggested initial dose range.

0.5 mg twice daily increasing to 1.0 mg twice daily or three times daily.

Usual maintenance dose.

3.0 mg to 20 mg daily in divided doses.
The following are given as guides to administration.

Patients receiving no antihypertensive therapy.

It is recommended that therapy be initiated at 0.5 mg twice daily for 3 days. Unless the patient is unusually sensitive, this dose should be increased to 1.0 mg twice daily or three times daily for a further 3 days and then to 2.0 mg twice daily or three times daily. Thereafter, as determined by the patient's response to the blood pressure lowering effect, the daily dose should be increased gradually to 20 mg. The optimal response may take up to 6 weeks. After initial titration some patients can be maintained on a twice daily dosage regimen.
A diuretic may be added to enhance the efficacy. It is recommended that this addition be considered when the prazosin dose is at 2 mg twice daily or three times daily.

Patients receiving diuretic therapy with inadequate control of blood pressure.

The diuretic should be reduced to a maintenance dose level for the particular agent, and prazosin initiated at 0.5 mg twice daily or three times daily. After the initial period of observation, the dose of prazosin should be gradually increased as determined by the patient's response.

Patients receiving other antihypertensive agents but with inadequate control.

Because some additive effect is anticipated, the dosage level of other agents (e.g. beta-adrenergic blocking agent, alpha-methyldopa, reserpine, clonidine*, etc.) should be reduced and prazosin initiated at 0.5 mg twice daily. Subsequent dosage increase should be made depending upon the patient's response.
Though experience is limited, there is evidence that adding prazosin to beta-adrenergic blocking agents, calcium channel blockers or angiotensin converting enzyme (ACE) inhibitors may bring about a substantial reduction in blood pressure. Thus, the low initial dose regimen is strongly recommended.
* Termination of oral therapy should be gradual (e.g. over more than 7 days). Sudden cessation of antihypertensive therapy is known to be associated with rebound hypertension which in some cases may be severe. This may occur with clonidine particularly in patients receiving more than 900 microgram/day.

Congestive heart failure.

Suggested initial daily dose range.

0.5 mg increasing to 4.0 mg in divided doses.

Usual daily maintenance dose.

4.0 mg to 20 mg in divided doses.
In recumbent patients the recommended starting dose is 0.5 mg three or four times daily. Dosage should be titrated according to the patient's clinical response, based on careful monitoring of cardiopulmonary signs and symptoms or haemodynamic studies when indicated. Dosage titration steps may be performed as often as every 2 to 3 days in patients under close medical supervision. In severely ill, decompensated patients, rapid dose titration over 1 or 2 days may be indicated, and is best done when haemodynamic monitoring is available. In clinical studies to date the mean optimal daily dose during the initial treatment period was 11.5 mg, with therapeutic dosages ranging from 4 mg to 20 mg daily in divided doses. Retitration may be required in some patients to maintain optimal clinical improvement.

Raynaud's phenomenon and Raynaud's disease.

Suggested starting dosage.

0.5 mg twice daily.

Usual daily maintenance dosage.

1 mg or 2 mg twice daily. The recommended starting dosage is 0.5 mg twice daily given for a period of 3 to 7 days. Dosage should be adjusted according to the patient's clinical response.

Benign prostatic hyperplasia.

The recommended starting dose is 0.5 mg twice daily, given for a period of 3 to 7 days and then adjusted according to clinical response. The maintenance dosage is 2 mg twice daily. The use of doses over 4 mg daily has not been studied, and cannot be recommended at present. Doses up to 4 mg daily have produced amelioration of symptoms for periods of up to 4 weeks but currently longer term data are not available. Postural hypotension may occur (see Section 4.4 Special Warnings and Precautions for Use, General (all patients)).

Dosage adjustment in renal impairment.

For patients with moderate to severe grades of renal impairment, evidence to date shows that prazosin does not further compromise renal function when used in patients with renal impairment. Because some patients in this category have responded to small doses of prazosin, it is recommended that therapy be initiated at 0.5 mg daily and that dose increases be instituted with caution.

4.3 Contraindications

Minipress is contraindicated in patients with a known sensitivity to quinazolines, prazosin or any other component of the tablets.

4.4 Special Warnings and Precautions for Use

General (all patients).

Syncope.

Minipress may cause syncope with - sudden loss of consciousness. In most cases this is believed to be due to an excessive postural hypotensive effect although occasionally the syncopal episode has been preceded by a bout of severe tachycardia with heart rates of 120-160 beats per minute. Syncopal episodes have usually occurred within 30 to 90 minutes of the initial dose of the drug: occasionally they have been reported in association with rapid dosage increases or the introduction of another antihypertensive drug into the regimen of a patient taking high doses of Minipress. The incidence of syncopal episodes is approximately 1% in patients given an initial dose of 2 mg or greater. Clinical trials conducted during the investigational phase of this drug suggest that syncopal episodes can be minimised by limiting the initial dose of the drug to 0.5 mg, by subsequently increasing the dosage slowly and by introducing any additional antihypertensive drugs into the patient's regimen with caution (see Section 4.2 Dose and Method of Administration). Hypotension may develop in patients given Minipress who are also receiving a beta-blocker or a diuretic.
Addition of a diuretic or other antihypertensive agent to Minipress therapy has been shown to cause an additive hypotensive effect. This effect can be minimised by reducing the dose of Minipress to 1 mg or 2 mg twice daily, by introducing additional antihypertensive drugs cautiously and then retitrating Minipress based on clinical response.
If syncope occurs, the patient should be placed in the recumbent position and treated supportively as necessary. This adverse effect is self limiting and in most cases does not recur after the initial period of therapy or during subsequent dose titration.
Patients should always be started at a dose of 0.5 mg of Minipress. The 2 mg and 5 mg tablets are not indicated for initial therapy. Both lying and standing blood pressure should be measured.
More common than loss of consciousness are the symptoms often associated with lowering of the blood pressure, namely, dizziness and lightheadedness. The patient should be cautioned about these possible adverse effects and advised what measures to take should they develop. The patient should also be cautioned to avoid situations where injury could result should syncope occur during the initiation of Minipress therapy.

Priapism.

Prolonged erections and priapism have been reported with alpha-1 blockers, including prazosin, in postmarketing experience. In the event of an erection that persists longer than 4 hours, the patient should seek immediate medical assistance. If priapism is not treated immediately, penile tissue damage and permanent loss of potency could result.

Patients with Raynaud's phenomenon or Raynaud's disease.

Because prazosin decreases peripheral vascular resistance, careful monitoring of blood pressure during initial administration and titration of Minipress is suggested (see Section 4.4 Special Warnings and Precautions for Use, General (all patients)).

Patients with congestive heart failure.

In patients with acute or chronic left ventricular failure who have undergone vigorous diuretic and vasodilator treatment, the resultant decrease in left ventricular filling may be associated with a significant fall in cardiac output and systemic blood pressure when Minipress is administered. In such patients, a low initial dose of Minipress and gradual titration with close observation is recommended (see Section 4.2 Dose and Method of Administration).
The haemodynamic response to Minipress in patients with congestive heart failure should be carefully monitored to ensure sustained clinical improvement as rapid attenuation of improved cardiac performance might occur in some patients.
In occasional patients the clinical efficacy of Minipress has been reported to diminish due to complete or partial tolerance to haemodynamic effects of prazosin. Evidence of efficacy for periods exceeding 6 months is lacking. In these patients, there is usually evidence of weight gain or peripheral oedema, indicating fluid retention. Since spontaneous deterioration may occur in such severely ill patients, a causal relationship to Minipress therapy has not been established. Thus, as with all patients with congestive cardiac failure, careful adjustment of diuretic dosage according to the patient's clinical condition is required to prevent excessive fluid retention and consequent recurrence of symptoms. In those patients without evidence of fluid retention, when clinical improvement has diminished, an increase in the dosage of Minipress, temporary withdrawal of the drug and/or addition of an aldosterone antagonist (e.g. spironolactone) to the treatment regimen will usually restore clinical efficacy.

Use in patients with congestive heart failure.

Minipress is not recommended in the treatment of congestive heart failure due to mechanical obstruction such as aortic valve stenosis, mitral valve stenosis, pulmonary embolism and restrictive pericardial disease. Adequate data are not yet available to establish efficacy in patients with congestive cardiac failure due to a recent myocardial infarction.

Patients with benign prostatic hyperplasia.

Minipress decreases peripheral vascular resistance, and since many patients with this disorder are elderly, standing and lying blood pressure should be carefully monitored during initial administration and during adjustment of the dose of Minipress (see Section 4.4 Special Warnings and Precautions for Use, General (all patients)). Close observation is especially recommended for patients taking medications that are known to lower blood pressure.

Patients with angina.

Minipress should be used cautiously in patients with ischaemic heart disease as angina may be exacerbated.

Use in hepatic impairment.

There are no data available on the use of Minipress in liver disease. However, as the drug is primarily metabolised by the liver and excreted in the bile and faeces, patients with impaired hepatic function may require a lower dose.

Use in renal impairment.

See Section 4.2 Dose and Method of Administration, Dosage adjustment in renal impairment.

Use in the elderly.

See Section 4.4 Special Warnings and Precautions for Use, Patients with benign prostatic hyperplasia; Section 4.8 Adverse Effects (Undesirable Effects), Serious or life-threatening reactions.

Paediatric use.

Minipress is not recommended for the treatment of children under the age of 12 years, since safe conditions for its use have not been established.

Effects on laboratory tests.

False positive results may occur in screening tests for phaeochromocytoma (urinary vanillylmandelic acid [VMA] and methoxyhydroxyphenylglycol [MHPG], urinary metabolites of noradrenaline) in patients who are being treated with Minipress.

4.5 Interactions with Other Medicines and Other Forms of Interactions

Patients taking phosphodiesterase type-5 inhibitors.

As with other alpha-1 blockers, concomitant administration of prazosin hydrochloride with a phosphodiesterase type-5 (PDE-5) inhibitor should be used with caution, as it may lead to symptomatic hypotension in a few susceptible individuals. No studies have been conducted with prazosin hydrochloride.

4.6 Fertility, Pregnancy and Lactation

Effects on fertility.

In long-term studies for 1 year or more, testicular changes, necrosis and atrophy, have occurred at 25 mg/kg/day in rats and dogs. This is 60 times the usual maximum recommended dose of 20 mg per day in humans. Testicular weight was marginally depressed but no morphological testicular changes were seen in dogs at a daily dose of 10 mg/kg which is 24 times the usual maximum recommended dose of 20 mg per day in humans.
In view of the testicular changes observed in animals, 105 patients on long-term therapy with Minipress were monitored for 17-ketosteroid excretion and no changes indicating a drug effect were observed. In addition no changes in sperm morphology suggestive of drug effect were seen in 27 males given Minipress alone for up to 51 months.
(Category B2)
When both male and female rats were treated with prazosin at a dose of 75 mg/kg/day and then mated, there was a significant impairment of fertility. There is no information available as to whether prazosin crosses the placenta. No teratogenic effects were seen in animal testing. However, the safety of Minipress used during pregnancy has not been established. Accordingly, it should be used only when, in the opinion of the physician, potential benefit to the pregnant patient outweighs potential risk.
Prazosin has been shown to appear in breast milk. Minipress should be administered to a nursing mother only when, in the opinion of the physician, the expected benefit outweighs any potential risk. Consideration should be given to not breastfeeding the baby.

4.7 Effects on Ability to Drive and Use Machines

Patients should be cautioned that their ability to drive or operate machinery may be impaired, especially when initiating prazosin therapy.

4.8 Adverse Effects (Undesirable Effects)

More common reactions.

Cardiovascular.

Postural hypotension (14%), palpitations (5%), oedema (4%).

Gastrointestinal.

Nausea (5%), dry mouth (4%).

General.

Lack of energy (7%), weakness (asthenia) (7%).

Nervous system.

Headaches (8%), drowsiness (8%), dizziness (faintness).

Ocular.

Blurred vision (4%).

Respiratory.

Nasal congestion (4%).

Less common reactions.

Body as a whole.

Allergic reaction, malaise, pain.

Cardiovascular.

Tachycardia (1%), syncope (1%), bradycardia, hypotension, vasculitis, angina pectoris.

Endocrine.

Gynaecomastia.

Dermatological.

Rash and pruritus (1%), alopecia, lichen planus, urticaria.

Gastrointestinal.

Vomiting (3%), constipation (3%), diarrhoea (2%), liver function abnormalities, pancreatitis, abdominal discomfort and/or pain.

Genitourinary.

Urinary incontinence, priapism, impotence, urinary frequency.

Nervous system.

Nervousness (2%), depression (2%), paraesthesiae, hallucinations, reddened sclera, tinnitus, worsening of pre-existing narcolepsy, vertigo, insomnia.

Respiratory.

Dyspnoea (2%), epistaxis.

General.

Fever, diaphoresis, positive ANA titre, arthralgia, flushing, eye pain.

Serious or life-threatening reactions.

Postural hypotension, especially in elderly patients with cerebrovascular disease, may be dangerous. Exacerbation of pre-existing angina, new onset angina and myocardial infarction have been associated with prazosin, although a causal relationship has not been established.

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 www.tga.gov.au/reporting-problems.

4.9 Overdose

Accidental ingestion of at least 50 mg of prazosin in a 2 year old child resulted in profound drowsiness and depressed reflexes. No decrease in blood pressure was noted. Recovery was uneventful.
Should overdosage lead to hypotension, support of the cardiovascular system is of first importance. Restoration of blood pressure and normalisation of heart rate may be accomplished by keeping the patient in the supine position. If this measure is inadequate, shock should first be treated with volume expanders. If necessary, vasopressors should then be used. Renal function should be monitored and supported as needed. Laboratory data indicate prazosin is not dialysable because it is protein bound.
For information on the management of overdose, contact the Poison Information Centre on 131126 (Australia).

5 Pharmacological Properties

5.1 Pharmacodynamic Properties

Mechanism of action.

Prazosin causes a decrease in total peripheral resistance. Animal studies suggest that the vasodilator effect of prazosin is related to blockade of postsynaptic alpha-adrenoceptors. The results of dog forelimb experiments demonstrate that the peripheral vasodilator effect is confined mainly to the level of the resistance vessels (arterioles). Unlike conventional alpha-blockers, the antihypertensive action of prazosin is usually not accompanied by reflex tachycardia.
Haemodynamic studies have been carried out in hypertensive patients following acute single dose administration and during the course of long-term maintenance therapy. The results confirm that the usual therapeutic effect is a fall in blood pressure, unaccompanied by a clinically significant change in cardiac output, heart rate, renal blood flow, and glomerular filtration rate. There is no measurable negative chronotropic effect.
Prazosin may increase plasma renin activity in patients with congestive heart failure.
Clinically, the antihypertensive effect is believed to be a direct result of peripheral vasodilation. In humans, blood pressure is lowered in both the supine and standing positions. This effect is more pronounced on the diastolic blood pressure. Tolerance does not appear to develop in long-term clinical use in the treatment of hypertension.
Rebound elevation of blood pressure does not occur following abrupt cessation of Minipress therapy.
A variety of epidemiologic, biochemical and experimental studies have suggested that an elevated level of low density lipoprotein (LDL) cholesterol may be associated with an increased risk of coronary heart disease. There is also evidence that reduced levels of high density lipoprotein (HDL) cholesterol may be associated with an increased risk of coronary heart disease. Clinical studies have shown that Minipress therapy is not associated with adverse changes in the serum lipid profile.
Haemodynamic studies carried out in patients with congestive heart failure following acute oral dosing and during the course of longer-term maintenance therapy, both at rest and on exercise, indicate that the therapeutic effect in these patients is due to a reduction in left ventricular filling pressure, reduction in cardiac impedance, and an augmentation of cardiac output. These effects, as indicated in forearm plethysmographic studies in humans, are associated with a balanced vasodilator effect on both resistance vessels (arterioles) and capacitance vessels (veins). The use of Minipress in the treatment of congestive heart failure does not provoke a reflex tachycardia.
Enucleated hyperplastic glandular tissue and hypertrophied muscular tissue removed from the enlarged prostate gland is rich in alpha-adrenoceptor content. Variations in the tone of smooth muscle in the prostate will produce variations in the closure pressure exerted on the prostatic urethra. This finding has provided the basis of pharmacological treatment of benign prostatic hyperplasia (BPH) involving alpha-adrenoceptor antagonism.
There is evidence of statistically significant improvement in urinary flow following Minipress therapy in patients with BPH. There is also evidence for a reduction in the volume of residual bladder urine and improvement in symptoms of BPH such as frequency of micturition.
Raynaud's phenomenon and Raynaud's disease have been successfully treated with Minipress. The vasodilator action of the drug may increase blood flow to affected parts to reduce the severity of the signs and symptoms and the frequency and duration of the attacks.

Clinical trials.

No data available.

5.2 Pharmacokinetic Properties

Absorption.

Following oral administration to normal volunteers and hypertensive patients, plasma concentrations reach a peak in 1 to 2 hours, with a plasma half-life of 2 to 3 hours. Pharmacokinetic data in a limited number of patients with congestive heart failure, most of whom showed evidence of hepatic congestion, indicate that peak plasma concentrations are reached in 2.5 hours and plasma half-life is approximately 7 hours. The bioavailability of oral prazosin was also increased 2-3 times in patients with congestive heart failure but the time to reach the peak was not affected in patients compared to normal volunteers. The mechanism of increase in plasma half-life and bioavailability of prazosin in congestive heart failure has not been satisfactorily explained.

Metabolism.

The drug is highly bound to plasma protein. Animal studies indicate that prazosin is extensively metabolised primarily by demethylation and conjugation. Less extensive human studies suggest similar metabolism in man.

Excretion.

Prazosin is excreted mainly via the bile and faeces.

5.3 Preclinical Safety Data

Genotoxicity.

No data available.

Carcinogenicity.

No data available.

6 Pharmaceutical Particulars

6.1 List of Excipients

Calcium hydrogen phosphate, maize starch, microcrystalline cellulose, magnesium stearate, sodium lauryl sulfate. The 1 mg tablet also contains sunset yellow FCF.

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 Australian Register of Therapeutic Goods (ARTG). The expiry date can be found on the packaging.

6.4 Special Precautions for Storage

Store below 30°C.

6.5 Nature and Contents of Container

PVC/Al blister packs of 100 tablets.

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

Prazosin hydrochloride is a white or almost white powder, very slightly soluble in water, slightly soluble in alcohol and in methanol, practically insoluble in acetone.
Minipress (prazosin hydrochloride), a quinazoline derivative, was the first antihypertensive of its chemical class. It is the hydrochloride salt of 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(-2-furoyl) piperazine. Molecular weight is 419.87.

Chemical structure.

Its structural formula is:

CAS number.

19237-84-4.

7 Medicine Schedule (Poisons Standard)

S4.

Summary Table of Changes