Consumer medicine information

Bactrim DS Tablets and Bactrim Oral Suspension

Sulfamethoxazole; Trimethoprim


Brand name


Active ingredient

Sulfamethoxazole; Trimethoprim




Consumer medicine information (CMI) leaflet

Please read this leaflet carefully before you start using Bactrim DS Tablets and Bactrim Oral Suspension.

What is in this leaflet

This leaflet answers some common questions about BACTRIM DS tablets and BACTRIM oral suspension (mixture is another name that can be used instead of oral suspension). It does not contain all the available information.

It does not take the place of talking to your doctor or pharmacist.

All medicines have risks and benefits. Your doctor has weighed the risks of you taking BACTRIM against the benefits they expect it will have for you.

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

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

What BACTRIM is used for

BACTRIM contains the active ingredients sulfamethoxazole and trimethoprim, also known as co-trimoxazole.

BACTRIM is used to treat bacterial infections in different parts of the body.

BACTRIM belongs to a group of medicines called antibiotics. There are many different types of medicines used to treat bacterial infections. Sulfamethoxazole in BACTRIM belongs to a group of medicines known as sulfonamides. Trimethoprim belongs to a group of medicines known as the benzylpyrimidines.

BACTRIM works by stopping the growth of the bacteria causing the infection.

BACTRIM does not work against infections caused by viruses, such as colds and flu.

BACTRIM has been prescribed for your current infection. Another infection later on may require a different medicine.

Your doctor may have prescribed BACTRIM for another purpose.

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

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

Before you take BACTRIM

When you must not take it

Do not take BACTRIM if:

  • you have had an allergic reaction to sulfamethoxazole, trimethoprim, any other sulfonamide, or any of the ingredients listed at the end of this leaflet.
    Some of the symptoms of an allergic reaction may include:
    - skin rash
    - peeling of the skin
    - itching or hives
    - swelling of the face, lips or tongue which may cause difficulty in swallowing or breathing
    - wheezing or shortness of breath.
  • you have severe liver or kidney disease, any blood disorder or megaloblastic anaemia
  • the child you are treating is less than 3 months of age
  • you have streptococcal pharyngitis
  • the package is torn or shows signs of tampering
  • you are taking dofetilide, a medicine used to treat irregular heartbeats
  • the expiry date (EXP) printed on the pack has passed
    If you take this medicine after the expiry date has passed, it may not work as well.

If you are not sure if you should be taking BACTRIM, talk to your doctor.

Before you start to take it

Your doctor must know about all the following before you can start to take BACTRIM.

Tell your doctor if:

  • you are pregnant or intend to become pregnant
    If BACTRIM is taken during pregnancy, it may harm the baby. Your doctor will discuss the risks and benefits of taking BACTRIM during pregnancy.
  • you are breast-feeding or plan to breast-feed
    BACTRIM passes into breast milk. Your doctor will discuss the risks and benefits of taking BACTRIM while breast-feeding.
  • you have any other health problems including:
    - an allergic reaction to any diuretic (fluid) tablet or medicines for diabetes or overactive thyroid. This may increase your chances of an allergic reaction to BACTRIM
    - any type of blood disorder (including porphyria and glucose-6-phosphate dehydrogenase deficiency)
    - kidney or liver disease
    - a hereditary disorder called phenylketonuria
    - epilepsy (fits or convulsions)
    - asthma
    - allergic disorders
    - rheumatoid arthritis
    - urinary obstruction
    - folic acid deficiency
  • you are allergic to any other medicines, foods, dyes or preservatives

Taking other medicines

Tell your doctor if you are taking any other medicines including any that you have bought from a pharmacy, supermarket or healthfood shop.

Some medicines may interfere with BACTRIM. These medicines include:

  • medicines used to treat diabetes such as repaglinide, rosiglitazone, pioglitazone, glibenclamide, gliclazide, glipizide, chlorpropamide and tolbutamide
  • fluid tablets (diuretics)
  • phenytoin, a medicine for epilepsy
  • pyrimethamine, a medicine for malaria
  • other medicines used to treat infections such as rifampicin, dapsone and polymyxin
  • zidovudine, a medicine to treat HIV infection
  • cyclosporin, a medicine used to treat organ transplant patients
  • warfarin, acenocoumarol, phenprocoumon, medicines used to thin the blood
  • medicines used to treat certain heart conditions such as digoxin and amiodarone
  • amantadine, a medicine used to treat the influenza virus and Parkinson's Disease
  • memantine, a medicine used to treat Parkinson's disease
  • 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, 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.

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

Your doctor or pharmacist has more information on medicines to be careful with or avoid while taking BACTRIM.

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

Use in very young children

BACTRIM should not be given to premature babies or children younger than 3 months of age.

Use in People Over 65 Years

People over 65 years are more at risk of severe side effects when taking BACTRIM. The risk is greater if you have kidney or liver disease or are taking some types of other medicines, such as diuretics.

Use in People with HIV infection

People with HIV infection have been reported to get more side effects while being treated with BACTRIM than people without HIV.

How to take BACTRIM

Follow all directions given to you by your doctor or pharmacist carefully. They may differ from the information contained in this leaflet.

How much to take

Take BACTRIM exactly as your doctor has prescribed.

Your doctor will tell you how much BACTRIM to take each day.

The dose and length of time you have to take BACTRIM will depend on the type of infection you have.

For adults and children over 12 years, the usual dose of BACTRIM DS is one tablet twice per day.

For children under 12 years of age, the dose of BACTRIM oral suspension depends on the age and weight of your child. Your doctor or pharmacist will tell you how much your child should be given.

How to take it

Swallow BACTRIM DS tablets whole (or halve them if necessary) with a glass of water.

The correct amount of BACTRIM oral suspension should be measured, using a metric measure, before being given by mouth.

When to take it

Take BACTRIM DS tablets or oral suspension after a meal.

How long to take BACTRIM

Continue taking BACTRIM until your doctor tells you to stop. The full course of BACTRIM prescribed by your doctor should be taken, even if you feel better after a few days. This will help clear your infection completely.

If your symptoms do not improve within a few days, or if they become worse, let your doctor know.

If you forget to take BACTRIM

Do not take an extra dose. Wait until the next dose and take your normal dose then.

Do not try to make up for the dose that you missed by taking more than one dose at a time.

If you are not sure what to do, ask your doctor or pharmacist.

In case of an overdose

Immediately telephone your doctor or Poisons Information Centre (telephone 13 11 26) for advice or go to Accident and Emergency at your nearest hospital if you think that you or anyone else may have taken too much BACTRIM even, if there are no signs of discomfort or poisoning. You may need urgent medical attention.

If you take too much BACTRIM, you may feel sick or vomit, feel dizzy, depressed or confused or have a headache. You may also feel drowsy or become unconscious.

Keep telephone numbers for these places handy.

If you are not sure what to do, contact your doctor or pharmacist.

While you are taking BACTRIM

Things you must do

Tell all doctors, dentists and pharmacists who are treating you that you are taking BACTRIM.

Tell your doctor if you become pregnant while taking BACTRIM.

Tell your doctor if, for any reason, you have not taken your medicine exactly as prescribed. Otherwise, your doctor may think that it was not effective and change your treatment unnecessarily.

Tell your doctor if you feel the tablets or oral suspension is not helping your condition.

Drink plenty of fluids while you are taking BACTRIM. This will help to flush the medicine through your system.

If you are taking BACTRIM for a long time, visit your doctor regularly so your progress can be checked. Your doctor may ask you to have regular tests to check your kidneys, liver or blood.

Tell your doctor you are taking BACTRIM if you have to have any blood tests. BACTRIM may affect the results of some blood tests.

Contact your doctor immediately if you get severe diarrhoea, even if it develops several weeks after stopping BACTRIM. DO NOT take any diarrhoea medicine without first checking with your doctor. Diarrhoea medicines may make your diarrhoea worse or make it last longer.

Things you must not do

Do not stop taking BACTRIM or change the dose without first checking with your doctor.

Do not let yourself run out of medicine over the weekend or on holidays.

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

Do not use BACTRIM to treat other complaints unless your doctor says to.

Do not take any other medicines whether they require a prescription or not without first telling your doctor or consulting with a pharmacist.

Things to be careful of

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

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

If you are going outdoors, wear protective clothing or use a SPF 15+ sunscreen. Your skin may burn more easily while you are taking BACTRIM.

Side Effects

Tell your doctor or pharmacist as soon as possible if you do not feel well while you are taking BACTRIM. BACTRIM helps most people with susceptible infections but it may have unwanted side effects in a few people.

All medicines can have side effects. Sometimes they are serious, most of the time they are not. You may need medical treatment if you get some of the side effects.

Ask your doctor or pharmacist to answer any questions you may have.

If side effects do occur, they may be:

  • nausea, with or without vomiting
  • diarrhoea or other abdominal (gut) or stomach discomfort

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 itchy vagina with vaginal discharge)

Your doctor will need to treat the thrush infection separately.

Tell your doctor immediately if you notice any of the following:

  • jaundice (yellowing of the skin)
  • severe or watery diarrhoea
  • any type of skin rash, peeling of the skin, severe itching or hives
  • fever, sore throat, lumps in the neck
  • cough, shortness of breath
  • severe persistent headache
  • discolouration of urine
  • swelling of the face and throat

These symptoms are usually rare but may be serious and need urgent medical attention.

Very rarely, people have died from complications due to certain severe skin, liver or blood reactions. Elderly people, people with liver or kidney disease and people taking certain other medicines are more at risk of these severe reactions.

Other rare side effects include:

  • other allergic reactions
  • pins and needles in the hands and feet
  • loss of appetite, fits, headaches, depression, imagined sensations or nervousness
  • increased or decreased urine production
  • unsteadiness or dizziness
  • sleeplessness, weakness, tiredness, increased sensitivity to light and stomach pains.

If you experience any of these effects 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.

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

After taking BACTRIM


Keep your BACTRIM DS tablets in the blister pack until it is time to take them.

Keep the oral suspension in the bottle until it is time to take it. If you take the tablets out of the blister pack or the oral suspension out of the bottle before it is time to take them, they may not keep well.

Keep BACTRIM in a cool dry place where the temperature stays below 30°C.

Do not store it, or any other medicine, in a bathroom or near a sink.

Do not leave it in the car or on window sills. Heat and dampness can destroy some medicines.

Keep BACTRIM where young children cannot reach it. A locked cupboard at least one-and-a-half metres above the ground is a good place to store medicines.


If your doctor tells you to stop taking BACTRIM, or the tablets or oral suspension has passed its expiry date, ask your pharmacist what to do with any medicine that is left over.

Product Description


BACTRIM is available as tablets (800 mg/ 160 mg) or as an oral suspension (mixture) 200 mg/ 40 mg per 5 mL).

BACTRIM comes in the following pack sizes:

  • BACTRIM DS - 10 tablets per carton
  • BACTRIM oral suspension - 100 mL per bottle

What BACTRIM looks like

BACTRIM DS tablets are white to almost white, oblong, with a breakline on one side and "ROCHE 800 + 160" on the other side.

The tablets have a breakline so that they can be broken in half if needed.

BACTRIM oral suspension is light beige in colour with a banana flavour.


Active ingredient

BACTRIM DS tablets and BACTRIM oral suspension contain the active ingredients trimethoprim and sulfamethoxazole.

  • each BACTRIM DS tablet contains 160 mg of trimethoprim and 800 mg of sulfamethoxazole.
  • each 5 mL of BACTRIM oral suspension contains 40 mg of trimethoprim and 200 mg of sulfamethoxazole.

Inactive ingredients

BACTRIM DS tablets also contain:

  • povidone (1201)
  • docusate sodium (480)
  • sodium starch glycollate
  • magnesium stearate (470)

BACTRIM DS tablets are gluten free and lactose free.

BACTRIM oral suspension also contains:

  • Cellulose - dispersible (460)
  • methyl hydroxybenzoate (218)
  • propyl hydroxybenzoate (216)
  • sorbitol solution (420)
  • polysorbate 80 (433)
  • banana flavour 85509 H
  • vanilla flavour 73690-36
  • water

BACTRIM oral suspension is gluten free and sugar free.


BACTRIM is distributed by:

Roche Products Pty Limited
ABN 70 000 132 865
Level 8, 30 - 34 Hickson Road
Sydney NSW 2000

Medical enquiries: 1800 233 950

Please check with your pharmacist for the latest Consumer Medicine Information.

Australian Registration numbers:

BACTRIM DS tablets:

  • AUST R 162563

BACTRIM Oral suspension:

  • AUST R 119404

This leaflet was prepared 29 April 2019.

Published by MIMS July 2019


Brand name


Active ingredient

Sulfamethoxazole; Trimethoprim




1 Name of Medicine

Sulfamethoxazole/ trimethoprim.

6.7 Physicochemical Properties

Bactrim is a synthetic antibacterial combination product.
The chemical name for sulfamethoxazole is 3-(4-aminobenzenesulfonamido)-5-methylisoxazole having a molecular weight of 253.28 and a pKa 5.9. The chemical name for trimethoprim is 2,4-diamino-5-(3,4,5-trimethoxybenzyl) pyrimidine having a molecular weight of 290.3 and a pKa 7.3.
Sulfamethoxazole is a white to off-white powder and is virtually insoluble in water at 20°C. Trimethoprim is a white to cream-coloured powder that has an aqueous solubility of 300 mg/L at 20°C.

Chemical structure.

CAS number.

Sulfamethoxazole: 723-46-6 and trimethoprim: 738-70-5.

2 Qualitative and Quantitative Composition

Bactrim DS tablets contain 800 mg sulfamethoxazole and 160 mg trimethoprim.
Bactrim oral suspension contains 200 mg sulfamethoxazole and 40 mg trimethoprim per 5 mL.

Excipients with known effect.

Bactrim oral suspension contains sorbitol 63% w/v.
For the full list of excipients, see Section 6.1 List of Excipients.

3 Pharmaceutical Form

Bactrim DS tablets are white to almost white, oblong, with a breakline on one side and "ROCHE 800 + 160" on the other side.
Bactrim oral suspension is light beige in colour with a banana flavor.

5 Pharmacological Properties

5.1 Pharmacodynamic Properties

Pharmacotherapeutic group: Combinations of sulfonamides and trimethoprim, incl. derivatives, ATC code: J01 EE01.

Mechanism of action.

Sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid. Trimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the required enzyme, dihydrofolate reductase. Thus, Bactrim blocks two consecutive steps in the biosynthesis of nucleic acids and proteins essential to bacteria.
Bactrim is effective against a wide range of Gram negative and Gram positive organisms, for example E. coli, Neisseria, Salmonella, Klebsiella-Enterobacter, Shigella, Vibrio cholerae, Bordetella pertussis, Streptococcus, Staphylococcus, Pneumococcus. Bactrim is usually active against the problem organisms Haemophilus influenzae and Proteus.
Bactrim is also active against the protozoan Pneumocystis jirovecii (see Section 4.2 Dose and Method of Administration). Bactrim is not active against Mycobacterium tuberculosis and Treponema pallidum. Pseudomonas aeruginosa is frequently insensitive. (See Table 4.)

Clinical trials.

No data available.

5.2 Pharmacokinetic Properties


Bactrim is rapidly absorbed on oral administration, reaching peak blood levels after 1 to 4 hours, which correspond to those achieved when each component is given alone. Absorption is complete as reflected by the absolute oral bioavailability reaching 100% for both trimethoprim and sulfamethoxazole. The mean serum half-lives of trimethoprim and sulfamethoxazole are 10 hours, and 8-10 hours, respectively.


The volume of distribution is approximately 1.6 L/kg for trimethoprim and approximately 0.26 L/kg for sulfamethoxazole, while the plasma protein binding reaches 37% for trimethoprim and 53% for sulfamethoxazole. The free forms of trimethoprim and sulfamethoxazole are considered to be the therapeutically active forms.
Studies in both animals and man have shown that diffusion of Bactrim into the tissue is good. Large amounts of trimethoprim and smaller amounts of sulfamethoxazole pass from the bloodstream into the interstitial fluid and other extravascular body fluids.
In humans, trimethoprim and sulfamethoxazole were detected in the foetal placenta, umbilical cord blood, amniotic fluid and foetal tissues (liver, lung), indicating placental transfer of both drugs (see Section 4.6 Fertility, Pregnancy and Lactation).


Around 30% of a trimethoprim dose is metabolised. The cytochrome P450 isoenzymes involved in the oxidative metabolism of trimethoprim have not been identified. The principal trimethoprim metabolites are 1 and 3-oxides and the 3' and 4'-hydroxy derivatives; some metabolites are active.
Around 80% of a sulfamethoxazole dose is metabolised in the liver, predominantly to the N4-acetyl derivative (~ 40% of the dose) and to a lesser extent by glucuronide conjugation. Sulfamethoxazole also undergoes oxidative metabolism. The first step of the oxidative pathway, which leads to the formation of the hydroxylamine derivative, is catalysed by CYP2C9. The metabolites are inactive.


The elimination half-lives of the two components are very similar (a mean of 10 hours for trimethoprim and 11 hours for sulfamethoxazole).
Both substances, as well as their metabolites, are eliminated almost entirely by the kidneys through both glomerular filtration and tubular secretion, giving urine concentrations of both active substances considerably higher than the concentration in the blood. Around two thirds of the trimethoprim dose and one quarter of the sulfamethoxazole dose are excreted unchanged into the urine. The total plasma clearance of trimethoprim equals 1.9 mL/min/kg. The total plasma clearance of sulfamethoxazole equals 0.32 mL/min/kg. A small part of the substances is eliminated via the faeces.

Pharmacokinetics in special populations.

Children and adolescents.

In children aged 1 to 9 years the total plasma clearance of trimethoprim is around threefold larger than in adults. As a consequence the half-life of trimethoprim in children is less than half of that observed in adults. Similar observations have been made for sulfamethoxazole (see Section 4.2 Dose and Method of Administration).

Hepatic impairment.

The pharmacokinetics of trimethoprim and sulfamethoxazole in patients with moderate or severe hepatic impairment are not significantly different from those observed in healthy subjects. (See Section 4.4 Special Warnings and Precautions for Use; Section 4.8 Adverse Effects (Undesirable Effects) for advice and experience of use in patients with impaired liver function.)

Patients with cystic fibrosis.

The renal clearance of trimethoprim and the metabolic clearance of sulfamethoxazole are increased in patients with cystic fibrosis. Consequently, the total plasma clearance is increased and the elimination half-life is decreased for both drugs.

5.3 Preclinical Safety Data


No data available.


No data available.

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.

4.3 Contraindications

Bactrim is contraindicated in patients showing marked liver parenchymal damage, blood dyscrasias, megaloblastic bone marrow or severe renal insufficiency, characterised by creatinine clearance < 15 mL/min (see Section 4.2 Dose and Method of Administration).
Bactrim should not be given to patients with a history of hypersensitivity to the active ingredients or the excipients, or other sulfonamides.
Bactrim must not be given to premature babies, nor during the first six weeks of life, because of the risk of producing kernicterus. It should probably not be given to children under 3 months of age.
Bactrim should not be used in the treatment of streptococcal pharyngitis. Clinical studies have documented that patients with group A β-haemolytic (Sp) streptococcal tonsillopharyngitis have a greater incidence of bacteriologic failure when treated with Bactrim than do those patients treated with penicillin, as evidenced by failure to eradicate this organism from the tonsillopharyngeal area.
Bactrim must not be given in combination with dofetilide (see Section 4.5 Interactions with Other Medicines and Other Forms of Interactions).

4.4 Special Warnings and Precautions for Use

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

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

Use in glucose-6-phosphate dehydrogenase deficiency.

In glucose-6-phosphate dehydrogenase deficient individuals, haemolysis may occur. This may be dose related. Bactrim should not be given to patients with a glucose-6-phosphate dehydrogenase deficiency unless absolutely essential, and then only in minimal doses.

Pseudomembranous colitis.

The use of Bactrim can lead in very rare instances to the development of severe colitis as a result of colonisation with C. difficile, a toxin producing organism. The colitis, which may or may not be accompanied by the formation of a pseudomembrane in the colon, can be fatal. If significant diarrhoea occurs (this may, however, begin up to several weeks after the cessation of antibiotic therapy), Bactrim should be discontinued. This may be sufficient treatment in the early stages although cholestyramine orally may help by binding the toxin in the colonic lumen. However, in moderate to severe cases appropriate therapy with a suitable oral antibacterial agent effective against C. difficile should be considered.
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 sulfonamide component.

Serious adverse reactions.

Fatalities, although rare, have occurred due to severe reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, drug rash with eosinophilia and systemic symptoms (DRESS), fulminant hepatic necrosis, agranulocytosis, aplastic anaemia and other blood dyscrasias.

Hypersensitivity and allergic reactions.

Bactrim should be discontinued if a skin rash appears. Clinical signs such as rash, sore throat, fever, arthralgia, cough, shortness of breath, pallor, purpura or jaundice may be early indications of serious reactions.
An adequate urinary output should be maintained at all times. Evidence of crystalluria in vivo is rare, although sulfonamide crystals have been noted in cooled urine from treated patients. In patients suffering from malnutrition, this risk may be increased.
As with other sulfonamide preparations, critical appraisal of benefit versus risk should be made in patients with liver damage, renal damage, urinary obstruction, blood dyscrasias, allergies or bronchial asthma.
Pulmonary infiltrates reported in the context of eosinophilic or allergic alveolitis may manifest through symptoms such as cough or shortness of breath. Should such symptoms appear or unexpectedly worsen, the patient should be re-evaluated and discontinuation of Bactrim therapy considered.

Long-term treatment.

If Bactrim is given over a prolonged period, regular blood counts are required. If a significant reduction in count of any formed blood element is noted, Bactrim should be discontinued.
As with all drugs containing sulfonamides, caution is advisable in patients with porphyria or thyroid dysfunction.
Patients who are 'slow acetylators' may be more prone to idiosyncratic reactions to sulfonamides.

Electrolyte abnormalities.

Close monitoring of serum potassium and renal function is warranted in patients receiving high dose Bactrim, as used in patients with Pneumocystis jirovecii pneumonia, or in patients receiving standard dose Bactrim with underlying disorders of potassium metabolism or renal insufficiency, or who are receiving drugs which induce hyperkalaemia (see Section 4.5 Interactions with Other Medicines and Other Forms of Interactions). Severe and symptomatic hyponatremia can occur in patients receiving Bactrim, particularly for the treatment of P. jirovecii pneumonia. Evaluation for hyponatremia and appropriate correction is necessary in symptomatic patients to prevent life threatening complications.
Sulfonamides, including Bactrim, may induce diuresis, particularly in patients with oedema of cardiac origin.
Cross sensitivity is known to occur among sulfonamides (see Section 4.3 Contraindications).
Except under careful supervision, Bactrim should not be given to patients with serious haematological disorders. Bactrim has been given to patients receiving cytotoxic therapy.
Because of possible interference with folate metabolism, 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 arthritics), in malabsorption syndromes, malnutrition states, or during the treatment of epilepsy with anticonvulsant drugs such as phenytoin, primidone or barbiturates. Changes indicative of folic acid impairment have, in certain specific situations, been reversed by folinic acid therapy.
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 in some patients.

Use in renal impairment.

In patients with renal impairment, a reduced or less frequent dosage is recommended in order to avoid accumulation of trimethoprim in the blood. Nonionic diffusion is the main factor in the renal handling of trimethoprim, and as renal failure advances, trimethoprim excretion decreases. See the special dosage table for use in renal impairment. Patients with severe renal impairment who are receiving Bactrim should be closely monitored for symptoms and signs of toxicity such as nausea, vomiting and hyperkalemia. Bactrim should be given with caution to patients with impaired renal function and to those with underlying disorders such as: possible folate deficiency; hypoglycaemia; electrolyte abnormalities (hyperkalemia).

Patients on peritoneal dialysis.

Peritoneal dialysis results in minimal clearance of administered trimethopim and sulfamethoxazole. Use of trimethoprim and sulfamethoxazole in patients receiving peritoneal dialysis is not recommended.

Use in the elderly.

The use of Bactrim 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 Bactrim is the antibacterial of choice in this age group.

Paediatric use.

No data available.

Effects on laboratory tests.

Two laboratory procedures, namely the Lactobacillus casei serum folate assay and the L. leishmanii serum vitamin B12 assay are affected by Bactrim.
Bactrim, 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 overestimations of about 10% in the range of normal values.

4.5 Interactions with Other Medicines and Other Forms of Interactions

Pharmacokinetic interactions.

Trimethoprim is an inhibitor of the organic cation transporter 2 (OCT2), and a weak inhibitor of CYP2C8. Sulfamethoxazole is a weak inhibitor of CYP2C9.
Systemic exposure to drugs transported by OCT2 may increase when coadministered with Bactrim. Examples include dofetilide, amantadine, memantine and lamivudine. See Table 2.

Pharmacodynamic interactions and interactions of undefined mechanism.

See Table 3.

4.6 Fertility, Pregnancy and Lactation

Effects on fertility.

No data available.
(Category C)
Sulfonamides may cause jaundice and haemolytic anaemia in the newborn. Sulfonamides may cause kernicterus in babies during the first month of life by displacing bilirubin from plasma albumin. Sulfonamides should therefore be avoided as far as possible during the last month of pregnancy (see Section 5.2 Pharmacokinetic Properties). Trimethoprim may interfere with folic acid metabolism and animal experiments have shown that administration of very high doses of trimethoprim during organ development may give rise to birth defects typical of folic acid antagonism. Two large observational studies have suggested a 2 to 3.5-fold increased risk of spontaneous abortion in women treated with trimethoprim alone and in combination with sulfamethoxazole during the first trimester compared to either no exposure to antibiotics or to exposure to penicillins. Bactrim should only be used during pregnancy if the potential benefit justifies the potential risk to the foetus. If Bactrim is used during pregnancy, or if the patient becomes pregnant while taking this drug, folic acid supplementation may be required. The patient should be appropriately counselled.
Both trimethoprim and sulfamethoxazole are excreted in breast milk at concentrations comparable or somewhat lower than that in the blood. Although the quantity of Bactrim ingested by a breastfed infant is small, it is recommended that the possible risks should be balanced against the expected therapeutic effect (see Section 5.2 Pharmacokinetic Properties). Consideration should be made of the infant's age (see Section 4.3 Contraindications).
A folate supplement may be considered with prolonged high doses of Bactrim.

4.8 Adverse Effects (Undesirable Effects)

The most common adverse effects are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions (such as rash (including maculopapular), pruritus and urticaria).
Fatalities associated with the administration of sulfonamides, although rare, have occurred due to severe reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anaemia and other blood dyscrasias (see Section 4.4 Special Warnings and Precautions for Use).


Agranulocytosis, aplastic anaemia, thrombocytopenia, leukopenia, neutropenia, haemolytic anaemia, autoimmune anaemia, megaloblastic anaemia, hypoprothrombinaemia, methaemoglobinaemia, eosinophilia, purpura, bone marrow depression, granulocytopenia and pancytopenia. Haematological changes have been observed particularly in the elderly. The great majority of these changes were mild, asymptomatic, and proved reversible on withdrawal of the drug which was, in some instances, necessary before therapy could be completed.
High doses of trimethoprim, as used in patients with Pneumocystis jirovecii pneumonia, induces progressive but reversible increase of serum potassium concentration in a substantial number of patients. Even treatment with recommended doses may cause hyperkalaemia when trimethoprim is administered to patients with underlying disorders of potassium metabolism, with renal insufficiency, or if drugs known to induce hyperkalaemia are given concomitantly. Cases of hyponatraemia have also been reported.

Allergic reactions.

Skin and systemic reactions may occur. Stevens-Johnson syndrome, fixed drug reaction, morbilliform rash, erythema and toxic epidermal necrolysis (Lyell's syndrome) have been reported.
The following have been reported rarely: eosinophilic or allergic alveolitis, anaphylaxis, allergic myocarditis, exfoliative dermatitis, angioedema, erythema multiforme, drug fever, chills, drug rash with eosinophilia and systemic symptoms (DRESS), Henoch-Schoenlein purpura, serum sickness-like syndrome, generalised allergic reactions, photosensitivity, conjunctival and scleral injection. In addition, polyarteritis nodosa and systemic lupus erythematosus have been reported.

Congenital disorders and pregnancy, puerperium and perinatal conditions.

Spontaneous abortion.


Hepatitis (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, isolated cases of vanishing bile duct syndrome, pseudomembranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhoea, anorexia, moniliasis. Jaundice has occurred rarely and has usually been mild and transient, frequently occurring in patients with a past history of infectious hepatitis.

General disorders and administration site conditions.

Venous pain and phlebitis.


Renal failure, impaired renal function, interstitial nephritis, BUN and serum creatinine elevation, toxic nephrosis with oliguria and anuria, and crystalluria.


Aseptic meningitis, meningitis like symptoms, convulsions, neuropathy (including peripheral neuritis and paraesthesia), ataxia, vertigo, tinnitus, headache and uveitis, vasculitis cerebral.


Hallucinations, depression, apathy, nervousness.


The sulfonamides 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 sulfonamides. Cases of hypoglycaemia in nondiabetic patients treated with Bactrim are seen rarely, usually occurring after a few days of therapy. Patients with renal dysfunction, liver disease, malnutrition, or those receiving high doses of Bactrim are particularly at risk.


Arthralgia, myalgia and isolated cases of rhabdomyolysis.


Pulmonary infiltrates, pulmonary vasculitis.

Vascular disorders.

Vasculitis, necrotizing vasculitis, granulomatosis with polyangiitis.


Weakness, fatigue, insomnia and fungal infections, such as candidiasis, retinal vasculitis.

Reporting of suspected adverse reactions.

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

4.2 Dose and Method of Administration


In acute infections, Bactrim (in any form) should be given for at least five days or until the patient has been symptom free for two days.

Adults and children over 12 years of age.

Standard dosage.

One Bactrim DS (double strength) tablet morning and evening after meals.

Minimum dosage.

Half a Bactrim DS (double strength) tablet twice daily (see below).

Maximum dosage (for particularly severe infections).

One and a half Bactrim DS (double strength) tablets twice daily.
The recommended dose for patients with documented Pneumocystis jirovecii pneumonitis is 20 mg/kg trimethoprim and 100 mg/kg sulfamethoxazole/24 hours given in equally divided doses every six hours for 14 days.

Special populations.

Paediatric populations.

Children under 12 years (see Section 4.3 Contraindications).

Under 2 years: 2.5 mL of syrup twice daily.
2-5 years: 2.5-5.0 mL of syrup twice daily.
6-12 years: 5.0-10.0 mL of syrup twice daily.
Adjustment of this dose can be made in the case of children whose bodyweight is particularly high or low.

Renal impairment.

The following dosage regimens are based on published information for the administration of Bactrim DS tablets to patients with reduced kidney function (see Table 1).

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.

4.9 Overdose



The amount of a single dose of Bactrim 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 sulfonamides 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.


Treatment of overdose should consist of general supportive measures.
General principles of treatment include the prevention of further absorption, forcing of oral fluids, and the administration of intravenous fluids if urine output is low and renal function is normal. Alkalinisation of the urine may aid the elimination of the sulfamethoxazole component of Bactrim but may decrease the elimination of the trimethoprim component. 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. On cessation of therapy calcium folinate 3 mg to 6 mg intramuscularly for five to seven days may be given to counteract the effects of trimethoprim on haematopoiesis.
Peritoneal dialysis is not effective and haemodialysis is only moderately effective in eliminating trimethoprim and sulfamethoxazole.


Use of Bactrim at high doses and/or for extended periods of time may cause bone marrow depression manifested as thrombocytopenia, leukopenia and/or megaloblastic anaemia. Other blood dyscrasias may occur due to folinic acid deficiency. If signs of bone marrow depression occur, the patient should be given leucovorin 5 to 15 mg daily until normal haematopoiesis is restored.
For information on the management of overdose, contact the Poisons Information Centre on 13 11 26 (Australia).

7 Medicine Schedule (Poisons Standard)


6 Pharmaceutical Particulars

6.1 List of Excipients

Bactrim DS tablets.

Povidone, docusate sodium, sodium starch glycollate, magnesium stearate.

Bactrim oral suspension.

Cellulose - dispersible, methyl hydroxybenzoate, propyl hydroxybenzoate, sorbitol solution, polysorbate 80, banana flavour 85509 H, vanilla flavour 73690-36, water.

6.2 Incompatibilities

Not applicable.

6.3 Shelf Life

Tablets: 5 years; Oral suspension: 5 years.

6.4 Special Precautions for Storage

Store below 30°C.

6.5 Nature and Contents of Container

Bactrim DS tablets are available in a blister pack of 10 tablets.
Bactrim oral suspension is available in a 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.

Summary Table of Changes