Updated 11 February 2013


Co-trimoxazole is an antibiotic that consists of a combination of two other antibiotics; trimethoprim and sulphamethoxazole.


Co-Trimoxazole is the active ingredient of Adco-Co-Trimoxazole, Bactrim, Bencole, Casicot, Cozole, Meditrim, Merck-Co-Trimoxazole, Micro-Co-Trimoxazole, Purbac, Sandoz Co-Trimoxazole, Septran and Trimethox.

General Information

Co-trimoxazole is an antibiotic that consists of a combination of two other antibiotics; trimethoprim and sulphamethoxazole. It is prescribed for treatment of urinary tract infections, respiratory tract infections, prostate infections, typhoid fever, cholera and acne, caused by susceptible organisms.

In years-gone-by co-trimoxazole was used extensively, but therapeutic effectiveness is decreasing as a result of bacterial resistance.

Gastro-intestinal side-effects, headache and nausea can be a result of both components of co-trimoxazole, while a skin rash, allergy and fever are less common. Allergic reactions are mostly the result of a sulphur allergy.

It is important to note that this medication is only effective against bacterial infections - if your infection is the result of a viral or fungal infection, it will be ineffective.

Antibiotic resistance - when bacteria develop the ability to defend themselves against the effect of an antibiotic - occurs frequently with many antibiotics. It mostly happens when patients do not complete the prescribed course in full, allowing bacteria to recover from treatment, and by using antibiotics for non-bacterial infections such as cold and flu.

How does co-Trimoxazole work?

Co-trimoxazole prevents bacterial DNA replication and transcription by inhibiting successive steps in bacterial folate synthesis.

Fast facts

Drug schedule: Schedule 4

Available as: Co-Trimoxazole is available as tablets, syrup and injection.

What does it do? Co-trimoxazole is an antibiotic.

Overdose risk: Medium

Dependence risk: Low

Is co-Trimoxazole available as a generic? Yes

Is co-Trimoxazole available on prescription only? No

User information

Onset of effect: Within 4 hours

Duration of action: Up to 12 hours

Dietary advice: This medication should be taken on an empty stomach; At least 8 glasses of water should be consumed every day while taking co-trimoxazole.

Stopping this medicine: Do not stop this medication until the prescribed dose has been completed; premature discontinuation may cause symptoms to recur.

Prolonged use: No problems expected; folic acid supplementation may be needed

Special precautions

Consult your doctor before using this drug if:

  • you have epilepsy
  • if you have liver or kidney disease
  • if you have a history of CNS disorders
  • if you suffer from Porphyria
  • if you have a pre-existing blood disorder
  • if you are allergic to any of the components in this drug
  • if you are taking any other medication.

Pregnancy: Avoid. Potential risk to the foetus has been reported. Consult your doctor before use, or if you are planning to fall pregnant.

Breastfeeding: Avoid. This medication is passed through breast milk and may affect your baby adversely. Consult your doctor before use.

Porphyria: Avoid. This medication may cause serious adverse effects. Consult your doctor before use.

Infants and children: This medication is safe for use in children at the recommended dose.

Elderly: Caution is advised in the elderly as side effects are more likely.

Driving and hazardous work: No special precautions need to be taken.

Alcohol: No special precautions need to be taken.

Possible side effects

Side effect


Consult your doctor



Only if severe

In all cases

Sin rash/ itch



Nausea/ vomiting



Diarrhoea/ abdominal pain















Fever/ sore throat



Abnormal bruising/ bleeding




Drug interactions


Increased risk of bleeding


Increased risk of renal toxicity


Increased risk of digoxin toxicity


Increased risk of lamivudine toxicity


Increased risk of antifolate effect

Oral contraceptives

Risk of contraceptive failure


Increased risk of phenytoin toxicity


Risk of cardiac effects

Oral antidiabetics

Increased low blood pressure effect


Increased risk of Rifampicin toxicity

Disease interactions

Consult your doctor before using this drug if you have epilepsy, liver or kidney disease, a history of CNS disorders, porphyria or if you are allergic to any of the components of this drug.

Overdose action

A small overdose is no cause for concern. In case of intentional large overdose, seek emergency medical attention. Symptoms may include nausea and confusion.

Recommended dosage

Adults: 160/ 800 mg (trimethoprim/sulphamethoxazole) 12 hourly. This may be increased to 240/1200 mg 12 hourly in severe infections.

Children 6 weeks to 5 moths: 20/100 mg 12 hourly;

Children 6 months to 5 years: 40/200 mg 12 hourly;

Children 6 - 12 years: 80/400 mg 12 hourly.


Get a quote


Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.

Live healthier

Too Tired? »

20 signs of burnout Staying active reduces stress 10 ways to have a healthier work day

Why you're exhausted

Lost your mojo? Here are 5 surprising energy drainers, plus the easy fixes that will help put the pep back in your step!