Consumer medicine information

Septrin Forte & Septrin Sugar-Free Paediatric Suspension

Trimethoprim; Sulfamethoxazole


Brand name

Septrin Sugar Free Oral Liquid

Active ingredient

Trimethoprim; Sulfamethoxazole




Consumer medicine information (CMI) leaflet

Please read this leaflet carefully before you start using Septrin Forte & Septrin Sugar-Free Paediatric Suspension.

What is in this leaflet

This leaflet answers some common questions about SEPTRIN. It does not contain all of the available information. It does not take the place of talking to your doctor or pharmacist.

Taking any medicine involves some risk. You doctor has weighted the risks of you using SEPTRIN against the benefits they expect it will have for you.

If you have any concerns about taking SEPTRIN, ask your doctor or pharmacist.

Keep this leaflet with the medicine. You may want to read it again.

What SEPTRIN is used for

SEPTRIN is used for the treatment of a variety of bacterial infections, including bronchitis and infections of the ear, sinus, kidney, bladder, stomach, bowel, skin and wounds.

Trimethoprim and sulfamethoxazole (the active ingredients in SEPTRIN) belong to a group of medicines called "anti-infectives". They work in slightly different ways to stop the growth of bacteria causing the infection.

If you have any questions about why you are taking SEPTRIN, ask your doctor or pharmacist. Your doctor may have prescribed it for another reason.

There is no evidence that this medicine is addictive.

SEPTRIN is only available with a doctor’s prescription.

Before taking it

When you must not take it

Do not use SEPTRIN if you have an allergy to:

  • trimethoprim
  • Sulfamethoxazole
  • any other sulfonamide (sulfur) antibiotic
  • Any of the ingredients listed at the end of this leaflet

Some of the symptoms of an allergic reaction may include: shortness of breath, wheezing or difficulty breathing; swelling of the face, lips, tongue which may cause difficulty in swallowing or breathing; rash, itching or hives, peeling of the skin.

Do not use SEPTRIN if:

You have severe liver or kidney disease, any blood disorder or megaloblastic anaemia.

The child you are treating is under 3 months of age.

You have streptococcal Pharyngitis.

You are taking dofetilide, a medicine used to treat irregular heartbeats.

Do not take SEPTRIN after the expiry date printed on the pack or bottle. SEPTRIN may have no effect if you take it after the expiry date.

Do not use SEPTRIN if the packaging appears to have been tampered with.

Do not use SEPTRIN to treat any other conditions unless advised by your doctor.

Do not give SEPTRIN to anyone else, even if their symptoms seem similar to yours.

Before you start to use it

You must tell your doctor if:

You are allergic to:

  • trimethoprim, sulfamethoxazole or any other ingredient listed at the end of this information.
  • any other sulphonamide type antibiotics, any diuretics (medicines that increase the volume of your urine), or medicines for diabetes or an overactive thyroid gland.

You are pregnant or breastfeeding or become pregnant, while taking SEPTRIN.

You have ever had any type of liver, kidney or bladder complaint or disease (eg. hepatitis).

You have ever had any type of blood disorder (including porphyria and glucose-6-phosphate dehydrogenase deficiency).

You have asthma or an allergic disorder.

You have a folic acid vitamin deficiency.

You have phenylketonuria.

You suffer from alcoholism.

You suffer from rheumatoid arthritis.

You are being treated for epilepsy (fits).

You have been diagnosed with AIDS. People with AIDS may not tolerate or respond to SEPTRIN in the same manner as someone who does not have AIDS. There may be an increase in the number and severity of side effects.

You are taking any medicines, including:

  • Any malaria medicines (eg. pyrimethamine)
  • Any diabetes medicines such as repaglinide, rosiglitazone, pioglitazone, glibenclamide, gliclazide, glipizide, chlorpropamide and tolbutamide
  • Any diuretics (diuretics)
  • Any epilepsy (fits) medicines (eg. phenytoin, primidone and some barbiturates)
  • Any medicines used to treat infections such as rifampicin, dapsone and polymyxin
  • Zidovudine, a medicine to treat HIV infection
  • Ciclosporin, a medicine used to prevent organ transplant rejections or to treat certain problems with the immune system
  • Warfarin, acenocoumarol, phenprocoumon, medicines used to thin the blood
  • Medicines used to treat some heart conditions such as digoxin and amiodarone
  • Amantadine, a medicine commonly used to treat the influenza virus and Parkinson's disease
  • Memantine, a medicine used to treat Parkinson's disease
  • Lamivudine, an antiretroviral medicine used to treat HIV/AIDS
  • Urinary acidifiers (for kidney conditions) oral contraceptives (‘the pill’)
  • Sulfinpyrazone, a medicine used to treat gout
  • Salicylates, medicines to treat conditions such as psoriasis or warts
  • Medicines used to treat cancer such as paclitaxel, mercaptopurine and methotrexate
  • Clozapine, a medicine used to treat schizophrenia
  • Medicines used to treat overactive thyroid conditions
  • Medicines used to treat depression such as imipramine, clomipramine, amitriptyline, dosulepin (dothiepin), doxepin, nortriptyline and trimipramine
  • Immunosuppressant medicines such as azathioprine and methotrexate
  • Medicines used to treat high blood pressure as well as a variety of heart and kidney conditions such as captopril, enalapril, lisinopril, fosinopril, perindopril, quinapril, ramipril, trandolapril, valsartan, telmisartan, irbesartan, candesartan, eprosartan, losartan, dofetilide and olmesartan
  • Procainamide

These medicines may be affected by SEPTRIN or may affect how well it works. You may need different amounts of your medicines, or you may need to take different medicines. Your doctor will advise you.

You are taking any other medicines, including medicines that you buy without a prescription from a pharmacy, supermarket or health food shop.

Your doctor will have a complete list of the medicines that may cause problems when taken with SEPTRIN.

SEPTRIN and very young children

SEPTRIN should not be used in premature babies nor during the first six weeks of life. It should probably not be given into infants less than 3 months of age.

SEPTRIN and the elderly

The use of SEPTRIN in elderly patients, particularly those with a liver or kidney disease or those taking certain other medicines such as diuretics, carries an increased risk of severe adverse reactions.

How to take it

How much to take

Take SEPTRIN as directed by your doctor or pharmacist.

For adults and children over 12 years old the usual dose is one SEPTRIN Forte Tablet, twice a day.

The dose of SEPTRIN Sugar-Free Paediatric Suspension for children under 12 years old depends on your child's weight and age. Your doctor or pharmacist will be able to tell you how much your child should be given.

Depending on the type of infection, and your overall health, your doctor may prescribe a different dose of SEPTRIN.

Always take the full course of SEPTRIN prescribed by your doctor.

How to take it

SEPTRIN Forte Tablets should be taken with a glass of water.

Do not crush or chew the tablets.

SEPTRIN Sugar-Free Paediatric Suspension should be shaken before use. The correct amount of the suspension should be measured before being given by mouth.

If you forget to take it

If it is almost time for your next dose, skip the dose that you have missed and take your next dose when you are supposed to.

Otherwise take the dose that you have missed as soon as you remember, then go back to your normal schedule.

If you have forgotten to take more than one dose, contact your doctor or pharmacist.

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

If you have trouble remembering when to take your medicine, ask your pharmacist for some hints.

If you take too much (overdose)

Immediately contact your doctor or Poisons Information Centre for advice, or go to Casualty at your nearest hospital, if you think that you or anyone else may have taken too much SEPTRIN. Do this even if there are no signs of discomfort or poisoning. You may need urgent medical attention.

Keep telephone numbers for these places handy.

If too much SEPTRIN has been taken signs and symptoms may include nausea, vomiting, dizziness, headache, depression and confusion. It is also possible that you will feel drowsy and you may lose consciousness.

While you are taking it

Things you must do

It is important that you drink plenty of fluids (water) while you are taking SEPTRIN.

Tell your doctor that you are taking SEPTRIN before you have any blood tests. If you are taking SEPTRIN over a long period, or you have kidney problems, your doctor may ask you to undergo regular blood and urine tests.

Your doctor or pharmacist will be able to tell you whether there are any other special instructions while you are taking SEPTRIN.

If you become pregnant while taking SEPTRIN, tell your doctor.

Tell your doctor if you fell the tablets is not helping your condition.

Tell your doctor or pharmacist immediately if you get severe diarrhoea, even if it occurs several weeks after stopping SEPTRIN.

Do not take any diarrhoea medicine without checking with your doctor. Diarrhoea may mean that you have a serious condition affecting your bowel. You may need urgent medical care.

Things you must not do

Do not stop taking SEPTRIN just because you feel better.

It is important that you take the full course of SEPTRIN prescribed by your doctor. This will reduce the risk of your infection recurring.

Your doctor will advise you when to stop taking SEPTRIN.

If you are unsure whether you should stop taking SEPTRIN, talk to your doctor or pharmacist.

Things to be careful of

Be careful driving or operating machinery until you know how SEPTRIN affects you.

Sometimes use of this medicine allows other bacteria and fungi which are not sensitive to SEPTRIN grow. If other infections such as thrush occur while you are taking SEPTRIN tell your doctor.

Be careful drinking alcohol while taking SEPTRIN. Combining SEPTRIN and alcohol can make you feel sick, vomit, or have stomach cramps, headaches and flushing. Your doctor may suggest you avoid alcohol while being treated with SEPTRIN.

Your skin may burn more easily while you are taking SEPTRIN. If outdoors, wear protective clothing or use a SPF 30+ sunscreen.

Side Effects

Stop taking SEPTRIN and tell your doctor immediately if you notice, or experience, any of the following (you may need urgent medical attention):

  • Any form of skin rash.
    The rash may indicate that you are allergic to SEPTRIN. In very rare circumstances, patients have died from complications that may arise from certain severe allergic reactions. Your doctor will know what action to take if you develop a severe reaction.
  • Severe fever, chills, sore throat, joint pains, cough or bruising.
  • Difficulty breathing or chest pains.
  • Severe, persistent diarrhoea. This is particularly important if there is any blood or mucus present. It is possible for this reaction to only become apparent several weeks after taking SEPTRIN.
  • Jaundice (yellowing of the skin), which is related to the function of your liver.
  • Severe persistent headache
  • Discolouration of urine

SEPTRIN may also cause more common side effects such as nausea, vomiting, diarrhoea or other abdominal (gut) or stomach discomfort and inflammation of the mouth or tongue.

These side effects are not usually serious or long lasting.

Tell your doctor if you notice these side effects and they worry you:

  • oral thrush (white, furry sore tongue and mouth)
  • vaginal thrush (sore and itchy vagina, vaginal discharge).

Your doctor will need to treat the thrush infection separately.

Other rare side effects include various other allergic side effects, pins and needles in the hands and feet, ringing in the ears, diarrhoea, loss of appetite, kidney damage, fits, headaches, depression, imagined sensations (hallucinations), nervousness, an increase or decrease in urine production, unsteadiness, dizziness, sleeplessness, weakness, tiredness, increased sensitivity to light and stomach pains.

If you experience any of these side effects, please contact your doctor as soon as possible.

This is not a complete list of all possible side effects. Others may occur in some people and there may be some side effects not yet known.

Tell your doctor if you notice anything else that is making you feel unwell, even if it is not on this list.

Ask your doctor or pharmacist if you don't understand anything in this list.

Various effects on the blood, particularly in the elderly, have been attributed to the use of SEPTRIN. In very rare circumstances, patients have died from some of these effects.

Having a blood test may be able to detect these effects.

Tell your doctor or pharmacist as soon as possible if you think you are experiencing any side effects from taking SEPTRIN.

Do not be alarmed by this list of possible side effects. You may not experience any of them.

After using it

If your doctor advises you to stop taking SEPTRIN, ask your pharmacist what to do with any SEPTRIN that you may have left.


Keep your tablets in a cool dry place where the temperature stays below 30°C. Protect the tablets from light.

Keep SEPTRIN Sugar-Free Suspension in a cool dry place where the temperature stays below 30°C. Protect the suspension from light.

Keep your SEPTRIN in the container it was supplied with.

Do not store SEPTRIN in the bathroom or near a sink. Heat and dampness may affect this medicine.

Do not leave SEPTRIN in the car on hot days.

Keep SEPTRIN and all other medicines, where children cannot reach them.

Product description

What it looks like

SEPTRIN Forte Tablets are white, elliptical, biconvex, and embossed “SEPTRIN FORTE” on the upper face and the bottom face is plain and scored along the shorter axis.

They are supplied in blister packs of 10 tablets.

SEPTRIN Sugar-Free Suspension is a thick, pink cherry flavoured liquid in a 100 mL bottle.


Each SEPTRIN Forte Tablet contains 160 mg of trimethoprim and 800 mg sulfamethoxazole.

The tablets also contain:

  • povidone
  • docusate sodium
  • sodium starch glycollate
  • magnesium stearate

Every 5 mL of Septrin Sugar-Free Paediatric Suspension contains 40 mg trimethoprim and 200 mg sulfamethoxazole.

The suspension also contains:

  • carmellose sodium
  • saccharin sodium
  • cellulose-dispersible
  • glycerol
  • polysorbate 80
  • citric acid - anhydrous
  • sorbitol
  • ethanol
  • water
  • sunset yellow FCF (CI 5985)
  • allura red AC (CI 16035)
  • Cherry Flavour Artif F1242 (PI 286)
  • methyl hydroxybenzoate
  • sodium benzoate

The suspension contains Methyl hydroxybenzoate, Sodium benzoate and Saccharin sodium.

The Australian Registration numbers are:

Septrin Forte Tablets: AUST R 10998

Septrin Sugar-Free Paediatric Suspension: AUST R 11000


Arrow Pharma Pty
Ltd 15-17 Chapel Street
Cremorne VIC 3121

This leaflet was revised in February 2022.

Published by MIMS April 2022


Brand name

Septrin Sugar Free Oral Liquid

Active ingredient

Trimethoprim; Sulfamethoxazole




1 Name of Medicine

Septrin 40/200 (trimethoprim/sulfamethoxazole) oral liquid.

2 Qualitative and Quantitative Composition

Septrin in an antibacterial combination containing trimethoprim and sulfamethoxazole in a ratio of 1:5.
Each 5 mL of Septrin Sugar Free Oral Liquid contains 40 mg trimethoprim and 200 mg sulfamethoxazole.
For the full list of excipients, see Section 6.1 List of Excipients.

3 Pharmaceutical Form

Septrin Sugar Free Oral Liquid is cherry flavoured.

4 Clinical Particulars

4.1 Therapeutic Indications

Upper and lower respiratory tract infections, renal and urinary tract infections, genital tract infections, gastrointestinal tract infections, skin and wound infections, septicaemias, and other infections caused by sensitive organisms.

4.2 Dose and Method of Administration

In the majority of acute infections, Septrin should be given for at least 5 days or until the patient has been symptom free for 2 days.


Children under 12 years.

6 to 12 years.

5 to 10 mL Septrin Paediatric Suspension every twelve hours.

2 to 5 years.

2.5 to 5 mL Septrin Paediatric Suspension every twelve hours.

Under 2 years.

2.5 mL Septrin Paediatric Suspension every twelve hours.
These amounts approximate to a dose of 6 mg/kg trimethoprim daily plus 30 mg/kg sulfamethoxazole daily. For severe infections dosage may be increased by 50%.

Treatment of Pneumocystis carinii pneumonitis.

The recommended dosage for patients with documented Pneumocystis carinii pneumonitis is 20 mg/kg trimethoprim and 100 mg/kg sulfamethoxazole per 24 hours given in equally divided doses every 6 hours for 14 days. The aim is to obtain peak plasma or serum levels of > 5 microgram/mL (see Section 4.8 Adverse Effects (Undesirable Effects)).

Use in the elderly.

See Section 4.4 Special Warnings and Precautions for Use.

Dosage in patients with reduced renal function.

The following dosage regimens have been published for the administration of Septrin to patients with reduced kidney function. See Table 1.

4.3 Contraindications

Septrin should not be given to patients with a history of sulphonamide or trimethoprim sensitivity.
Marked liver parenchymal damage or severe renal insufficiency, where repeated measurements of the plasma concentration cannot be performed.
Except under careful supervision, Septrin should not be given to patients with serious haematological disorders. Septrin has been given to patients receiving cytotoxic therapy (see Section 4.5 Interactions with Other Medicines and Other Forms of Interactions).
Septrin should not be used in late pregnancy because products containing a sulphonamide may cause kernicterus.
Septrin should not be given to premature babies or to infants less than 2 months of age.
Septrin should not be used in the treatment of streptococcal pharyngitis. Clinical studies have documented that patients with Group A Beta-haemolytic streptococcal tonsillopharyngitis have a greater incidence of bacteriologic failure when treated with Septrin than do those patients treated with penicillin, as evidenced by failure to eradicate this organism from the tonsillopharyngeal area.

4.4 Special Warnings and Precautions for Use

Fatalities associated with the administration of sulfonamides, although rare, have occurred due to severe reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anaemia and other blood dyscrasias.
Sulfonamides, including sulfonamide containing products such as trimethoprim/ sulfamethoxazole, should be discontinued at the first appearance of skin rash or any sign of adverse reaction. In rare instances, a skin rash may be followed by a more severe reaction such as Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic necrosis and serious blood disorder.
Clinical signs such as rash, sore throat, fever, arthralgia, cough, shortness of breath, pallor, purpura or jaundice may be early indications of serious reactions.
Cough, shortness of breath and pulmonary infiltrates are hypersensitivity reactions of the respiratory tract that have been reported in association with sulfonamide treatment.

Use in the elderly.

The use of Septrin in elderly patients carries an increased risk of severe adverse reactions. In rare instances fatalities have occurred. The risk of severe adverse reactions is particularly greater when complicating conditions exist, e.g. impaired kidney and/or liver function, or concomitant use of other drugs. Severe skin reactions, or generalised bone marrow suppression (see Section 4.8 Adverse Effects (Undesirable Effects)) or a specific decrease in platelets (with or without purpura) are the most frequently reported severe adverse reactions in elderly patients. In those concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported. Appropriate dosage adjustments should be made for patients with impaired kidney function (see Section 4.2 Dose and Method of Administration).
In view of the increased risk of severe adverse reactions in the elderly, consideration should be given to whether Septrin is the antibacterial of choice in this age group.

Use in treatment of Pneumocystis carinii pneumonitis in patients with acquired immunodeficiency syndrome (AIDS).

Because of their unique immune dysfunction, AIDS patients may not tolerate or respond to Septrin in the same manner as non-AIDS patients. The incidence of side effects, particularly rash, fever and leukopenia, with Septrin therapy in AIDS patients who are being treated for Pneumocystis carinii pneumonia has been reported to be greatly increased compared with the incidence normally associated with the use of Septrin in non-AIDS patients.

Use in glucose-6-phosphate dehydrogenase deficiency.

In individuals with glucose-6-phosphate dehydrogenase deficiency haemolysis may occur. This may be dose related.

Use in patients known or suspected to be at risk of acute porphyria.

The administration of Septrin to patients known or suspected to be at risk of acute porphyria should be avoided. Both trimethoprim and sulphonamides (although not specifically sulfamethoxazole) have been associated with clinical exacerbation of porphyria.

Pseudomembranous colitis.

Antibiotic associated pseudomembranous colitis has been reported with many antibiotics including trimethoprim/ sulfamethoxazole. A toxin produced with Clostridium difficile appears to be the primary cause. The severity of the colitis may range from mild to life threatening. It is important to consider this diagnosis in patients who develop diarrhoea or colitis in association with antibiotic use (this may occur up to several weeks after cessation of antibiotic therapy). Mild cases usually respond to drug discontinuation alone. However, in moderate to severe cases appropriate therapy with a suitable oral antibacterial agent effective against Clostridium difficile should be considered. Fluids, electrolytes and protein replacement should be provided when indicated.
Drugs which delay peristalsis (e.g. opiates and diphenoxylate with atropine (Lomotil)) may prolong and/or worsen the condition and should not be used.
Fluids, electrolytes, and protein replacement therapy should be provided when indicated.
Even if an organism is sensitive to trimethoprim, if it is not sensitive to sulfamethoxazole the combination should not be used, to avoid unnecessary exposure to the potential side effects of the sulphonamide components.
An adequate urinary output should be maintained at all times. Evidence of crystalluria in vivo is rare, although sulphonamide crystals have been noted in cooled urine from treated patients. In patients suffering from malnutrition this risk may be increased.
As with other sulphonamide preparations, critical appraisal of benefit versus risk should be made in patients with liver damage, renal damage, urinary obstruction, allergies or bronchial asthma. Severe hepatic parenchymal damage may result in changes in the absorption and metabolism of sulfamethoxazole and trimethoprim. In patients with renal impairment, a reduced or less frequent dosage is recommended in order to avoid accumulation of trimethoprim in the blood (see Section 4.2 Dose and Method Administration).
Nonionic diffusion is the main factor in the renal handling of trimethoprim, and as renal failure advances, trimethoprim excretion decreases. For such patients, serum assays are necessary. See the special dosage table for use in renal impairment.
Regular blood counts are advisable in patients on long-term therapy, in those who are predisposed to folate deficiency (i.e. the elderly, chronic alcoholics and rheumatoid arthritis), in malabsorption syndromes, malnutrition states, or during the treatment of epilepsy with anticonvulsant drugs such as phenytoin, primidone or barbiturates. Changes indicative of folate deficiency may be reversed by administration of folinic acid without interfering with the antibacterial activity of trimethoprim.
Special care should be exercised in treating elderly or suspected folate deficient patients; folate supplementation should be considered.
A folate supplement should also be considered with prolonged high dosage of Septrin. Urine analysis and renal function tests should be performed during long term therapy particularly in patients with reduced renal function.
The possibility of superinfection with a nonsensitive organism should be borne in mind.
Trimethoprim has been noted to impair phenylalanine metabolism, but this is of no significance in phenylketonuric patients on appropriate dietary restriction.

Paediatric use.

Safety has not been established in infants less than 2 months old and is not recommended for use. Trimethoprim and sulfamethoxazole should be used with caution in children who have the fragile X chromosome, as folate depletion may worsen the psychomotor regression associated with the disorder (see Section 4.3 Contraindications).

Effects on laboratory tests.

Septrin, specifically the trimethoprim component, can interfere with a serum methotrexate assay as determined by the competitive binding protein technique (CBPA) when a bacterial dihydrofolate reductase is used as the binding protein. No interference occurs, however, if methotrexate is measured by a radioimmunoassay (RIA).
The presence of trimethoprim and sulfamethoxazole may also interfere with the Jaffe alkaline picrate reaction assay for creatinine resulting in over estimations of about 10% in the range of normal values.
The Lactobacillus casei serum folate assay and the L. leishmanii serum vitamin B12 assay are affected by Septrin.

4.5 Interactions with Other Medicines and Other Forms of Interactions

In elderly patients concurrently receiving diuretics, mainly thiazides, there appears to be an increased incidence of thrombocytopenia with or without purpura.
Occasional reports suggest that patients receiving pyrimethamine as malarial prophylaxis at doses in excess of 25 mg weekly may develop megaloblastic anaemia should Septrin be prescribed concurrently.
Septrin has been shown to potentiate the anticoagulant activity of warfarin via stereo-selective inhibition of its metabolism. Sulfamethoxazole may displace warfarin from plasma albumin protein binding sites in vitro. Careful control of the anticoagulant therapy during treatment with Septrin is advisable.
Septrin prolongs the half-life of phenytoin and, if coadministered, the prescriber should be alert for excessive phenytoin effect. Close monitoring of the patient's condition and serum phenytoin levels is advisable.
Interaction with sulphonylurea hypoglycaemic agents is uncommon, but potentiation has been reported.
Concurrent use of rifampicin and Septrin results in a shortening of the plasma half-life of trimethoprim after a period of about one week.
Reversible deterioration in renal function has been observed in patients treated with Septrin and cyclosporin following renal transplantation.
Sulphonamides can displace methotrexate from plasma protein binding sites, thus increasing free methotrexate concentrations. If Septrin is considered appropriate therapy in patients receiving other antifolate drugs, such as methotrexate, a folate supplement should be considered (see Section 4.4 Special Warnings and Precautions for Use).
Cases of pancytopenia have been reported in patients taking trimethoprim/ sulfamethoxazole in combination with methotrexate. Most of these patients were on long-term methotrexate therapy and/or predisposed to folate deficiency, and none of them were reported to have received a prophylactic folinic acid supplement (see Section 4.4 Special Warnings and Precautions for Use).
Reversible deterioration in renal function has been observed in patients treated with cotrimoxazole and cyclosporin following renal transplantation.
When trimethoprim is administered simultaneously with drugs that form cations at physiological pH and are also partly excreted by active renal secretion (e.g. procainamide, amantadine), there is the possibility of competitive inhibition of this process which may lead to an increase in plasma concentration of one or both of the drugs.
Concomitant use of trimethoprim with digoxin has been shown to increase plasma digoxin levels in a proportion of elderly patients.

4.6 Fertility, Pregnancy and Lactation

Effects on fertility.

The effect of Septrin on human fertility is not known. Reproduction studies in rats with oral dosage up to 70 mg/kg/day trimethoprim plus 350 mg/kg/day sulfamethoxazole have not revealed evidence of impaired fertility.
(Category C)
Sulphonamides may cross the placenta and cause kernicterus, jaundice and haemolytic anaemia in the newborn (by displacing bilirubin from plasma albumin) and should therefore be avoided as far as possible during the last month of pregnancy. Trimethoprim and sulfamethoxazole may interfere with folic acid metabolism and exposure during organ development may give rise to birth defects typical of folic acid antagonism.
Trimethoprim and sulfamethoxazole, alone and in combination, have produced teratogenic effects (cleft palate) in some studies in rats receiving dosages exceeding the usual human dosage. In some rabbit studies, an overall increase in foetal loss was associated with trimethoprim doses 6 times the usual human dose. Septrin should be used in pregnancy only if the potential benefit justifies the potential risk to the foetus. If a trimethoprim/ sulphonamide combination is given during pregnancy, folic acid supplementation may be required.
Both trimethoprim and sulfamethoxazole are excreted in breast milk at concentrations comparable or somewhat lower than that in the blood. Sulfonamides may cause kernicterus, jaundice and haemolytic anaemia in the newborn. It is recommended that the possible risks should be balanced against the expected therapeutic effect. Consideration should be made of the infant's age. Premature babies or to infants less than 2 months of age should not be exposed to Septrin (see Section 4.3 Contraindications).

4.7 Effects on Ability to Drive and Use Machines

The effects of this medicine on a person's ability to drive and use machines were not assessed as part of its registration.

4.8 Adverse Effects (Undesirable Effects)

The following reactions have been reported from the use of oral Septrin.
Nausea, vomiting, stomatitis and glossitis may occur.
Haematological changes have been observed in some patients, particularly the elderly. The great majority of these changes were mild, asymptomatic, and proved reversible on withdrawal of the drug; in some instances, this was necessary before therapy could be completed. The reported changes consist primarily of neutropenia and thrombocytopenia. Observed less frequently: megaloblastic anaemia, leucopenia, aplastic and haemolytic anaemia, purpura, agranulocytosis and bone marrow depression. Rarely, fatalities have been reported.
Skin and systemic reactions may occur. Several cases of Stevens-Johnson syndrome and toxic epidermal necrolysis (Lyell's syndrome) have been reported. Fatalities have been reported rarely. Jaundice has also rarely occurred and has usually been mild and transient, frequently occurring in patients with a past history of infectious hepatitis.
On the whole, however, the nature of adverse reactions generally corresponds with what one would expect from a sulphonamide of moderately low toxicity, when the contraindications are strictly respected and recommended doses are used. Percentage incidence figures cannot be precise but have been estimated from the published literature at 6.8% of cases treated.
Sensitivity reactions and gastrointestinal symptoms comprised nearly three-quarters of the adverse reactions reported.
The following have been reported rarely; eosinophilic or allergic alveolitis, anaphylaxis, allergic myocarditis, angioedema, drug fever, chills, Henoch-Schonlein purpura, serum sickness-like syndrome, generalised allergic reactions, photosensitivity, conjunctival and scleral injection. In addition, periarteritis nodosa and systemic lupus erythematosus have been reported.
Hepatitis (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, pancreatitis, emesis, abdominal pain, diarrhoea, anorexia, moniliasis, pseudomembranous colitis.
Renal failure, interstitial nephritis, blood urea and serum creatinine elevation, toxic nephrosis with oliguria and anuria, and crystalluria.
Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache.
Hallucinations, depression, apathy, nervousness.
The sulphonamides bear certain chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides) and oral hypoglycaemic agents. Cross sensitivity may exist with these agents. Diuresis and hypoglycaemia have occurred rarely in patients receiving sulphonamides.
Arthralgia and myalgia, pulmonary infiltrates, weakness, fatigue, insomnia.
At the high dosages used for the therapy of Pneumocystis carinii pneumonitis in patients with acquired immune deficiency syndrome (AIDS), rash, fever, neutropenia, thrombocytopenia, raised liver enzymes, hyperkalaemia and hyponatraemia have been reported, necessitating cessation of therapy. If signs of bone marrow depression occur, the patient may be given calcium folinate supplementation. Severe hypersensitivity reactions have also been reported in HIV infected patients on re-exposure to cotrimoxazole, sometimes after a dosage interval of a few days.

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 and to also contact Apotex Medical Information Enquiries/Adverse Drug Reaction Reporting on 1800 195 055.

4.9 Overdose



The amount of a single dose of Septrin that is either associated with symptoms of overdosage or is likely to be life threatening has not been reported. Signs and symptoms of overdosage reported with sulphonamides include anorexia, colic, nausea, vomiting, dizziness, headache, drowsiness and unconsciousness. Pyrexia, haematuria and crystalluria may be noted. Blood dyscrasias and jaundice are potential late manifestations of overdosage.
Signs of acute overdosage with trimethoprim include nausea, vomiting, dizziness, headache, mental depression, confusion and bone marrow depression.


Use of Septrin at high doses and/or for extended periods of time may cause bone marrow depression manifested as thrombocytopenia, leukopenia and/or megaloblastic anaemia.



General principles of treatment include use of activated charcoal (where physiochemically appropriate) and the administration of intravenous fluids if urine output is low and renal function is normal. Acidification of the urine will increase renal elimination of trimethoprim. The patient should be monitored with blood counts and appropriate blood chemistries including electrolytes. If a significant blood dyscrasia or jaundice occurs, specific therapy should be instituted for these complications. Peritoneal dialysis is not effective and haemodialysis is only moderately effective in eliminating trimethoprim and sulfamethoxazole.


If signs of bone marrow depression occur, the patient should be given leucovorin; 5 to 15 mg daily has been recommended by some investigators.
For information on the management of overdose, contact the Poisons Information Centre on 13 11 26 (Australia).

5 Pharmacological Properties

5.1 Pharmacodynamic Properties

Mechanism of action.

Sulfamethoxazole competitively inhibits the utilisation of para-aminobenzoic acid in the synthesis of dihydrofolate by the bacterial cell resulting in bacteriostasis. Trimethoprim reversibly inhibits bacterial dihydrofolate reductase (DHFR), an enzyme active in the folate metabolic pathway converting dihydrofolate to tetrahydrofolate. Thus, trimethoprim and sulfamethoxazole block two consecutive steps in the biosynthesis of purines and therefore nucleic acids essential to many bacteria. This action produces marked potentiation of activity in vitro between the two agents.
Trimethoprim binds to plasmodial DHFR, but less tightly than to the bacterial enzyme. Its affinity for mammalian DHFR is some 50,000 times less than for the corresponding bacterial enzyme.

Clinical trials.

The majority of common Gram negative and Gram positive pathogenic bacteria are sensitive in vitro to trimethoprim and sulfamethoxazole at concentrations well below those reached in blood, tissue fluids and urine after the administration of recommended doses. These organisms include E. coli, Neisseria, Salmonella, Klebsiella, Enterobacter, Shigella, Vibrio cholerae and Bordetella pertussis, Streptococcus, Staphylococcus and Pneumococcus. Septrin is usually active against the problem organisms Haemophilus influenzae and Proteus. See Table 2.
Septrin is insensitive against Pseudomonas aeruginosa, Mycoplasma, Ureoplasma urealyticum, Mycobacterium tuberculosis, Bacteroides species, Lactobacillus species and Treponema pallidum.
In vitro studies have shown that bacterial resistance develops more slowly with Septrin (trimethoprim + sulfamethoxazole) than with either trimethoprim or sulfamethoxazole alone.
Septrin is also active against the protozoan Pneumocystis carinii (see Section 4.2 Dose and Method of Administration).
Satisfactory sensitivity testing is achieved only with recommended media free from inhibitory substances, especially thymidine and thymine.

Disc susceptibility testing.

Dilution or diffusion techniques, either quantitative (MIC) or breakpoint, should be used following a regularly updated, recognised and standardised method (e.g. NCCLS). Standardised susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures.
A report of "susceptible" indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable. A report of "intermediate" indicates that the result should be considered equivocal, and if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where high dosage of drug can be used. This category also provides a buffer zone, which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of "resistant" indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable; other therapy should be selected.

5.2 Pharmacokinetic Properties


After oral administration, trimethoprim and sulfamethoxazole are rapidly and nearly completely absorbed. Peak levels in the blood occur between one and four hours after ingestion and the level attained is dose related. Steady-state levels in adults are reached after dosing for 2-3 days. Neither component has an appreciable effect on the concentrations achieved in the blood by the other.
Trimethoprim is a weak base with a pKa of 7.3. It is lipophilic. Tissue levels of trimethoprim are generally higher than corresponding plasma levels, the lungs and kidneys showing especially high concentrations. Trimethoprim concentrations exceed those in plasma in the case of bile, prostatic fluid and tissue, saliva, sputum and vaginal secretions. Trimethoprim is found in the aqueous humour, breast milk, cerebrospinal fluid, middle ear fluid, synovial fluid and tissue (interstitial) fluid. Trimethoprim passes into amniotic fluid and foetal tissue, reaching concentrations approximating those of maternal serum.


Approximately 44-50% of trimethoprim in the plasma is protein bound.


The half-life in man is in the range 8.3-31 hours (mean 14.5 hours) in the presence of normal renal function. It is increased by a factor of 1.5-3.0 when the creatinine clearance is less than 10 mL/minute. There appears to be no significant difference in the elderly compared with young patients.


The principal route of excretion of trimethoprim is renal and approximately 50% of the dose is excreted in the urine within 24 hours as unchanged drug. Several metabolites have been identified in the urine. Urinary concentrations of trimethoprim vary widely.
Sulfamethoxazole is a weak acid with a pKa of 6.0. The concentration of active sulfamethoxazole in amniotic fluid, aqueous humor, bile, cerebrospinal fluid, middle ear fluid, sputum, synovial fluid and tissue (interstitial) fluid is of the order of 20-50% of the plasma concentration.
Approximately 66-70% of sulfamethoxazole in the plasma is protein bound. The half-life in man is in the range 6.1-22 hours (mean 11 hours) in the presence of normal renal function. There is no change in the half-life of active sulfamethoxazole with a reduction in renal function, but there is prolongation of the half-life of the major, acetylated metabolite when the creatinine clearance is below 25 mL/minute.
The principal route of excretion of sulfamethoxazole is renal; between 15% and 30% of the dose recovered in the urine is in the active form. In elderly patients, there is a reduced renal clearance of sulfamethoxazole.

5.3 Preclinical Safety Data


Bacterial mutagenic studies have not been performed with Septrin. Trimethoprim did not exhibit mutagenic activity in the Ames test, and no chromosomal damage was observed in human leukocytes cultured in vitro with trimethoprim concentrations exceeding those attained in blood during therapy with the drug.


Long-term studies in animals to evaluate the carcinogenic potential of Septrin have not been performed.

6 Pharmaceutical Particulars

6.1 List of Excipients

Septrin Sugar Free Oral Liquid: sorbitol, preservatives methyl hydroxybenzoate and sodium benzoate, ethanol, Cherry Flavour Artif F1242 (PI 286), sunset yellow, allura red, citric acid, cellulose, glycerol, polysorbate 80, sodium carmellose, saccharin sodium.

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. Protect from light.


Store below 30°C. Protect from light.

6.5 Nature and Contents of Container

Septrin Paediatric Suspension sugar free (cherry flavour): trimethoprim 40 mg/5 mL and sulfamethoxazole 200 mg/5 mL, pink suspension with a characteristic cherry odour. Free from undispersed material. 100 mL bottle (glass).

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

Trimethoprim is a white to light yellow, odourless, bitter compound.
Sulfamethoxazole is an almost white, odourless, tasteless compound.

Chemical structure.

Chemical Name: 2,4-diamino-5-(3,4,5,trimethoxybenzyl)-pyrimidine.
Molecular Formula: C14H18N4O3.
Molecular Weight: 290.3 g/mol.

CAS number.

Chemical Name: N1-(5-methyl-3-isoxazolyl) sulphanilamide.
Molecular Formula: C10H11N3O3S.
Molecular Weight: 253.28 g/mol.

CAS number.


7 Medicine Schedule (Poisons Standard)

S4 - Prescription Only Medicine.

Summary Table of Changes