co-trimoxazole: clinical use

Prescribing considerations

• Reserve use for circumstances where anticipated benefit outweighs risk and susceptibility is expected or established.
• Assess renal and hepatic function, folate status, current medicines and risks of electrolyte disturbance or fluid overload.
• Use additional caution in older people, malnutrition, G6PD deficiency, severe atopy, asthma and pre-existing haematological disease.
• Discontinue promptly if severe cutaneous, respiratory, haematological or systemic hypersensitivity features emerge.

Contraindications and cautions

• Hypersensitivity to trimethoprim, sulfamethoxazole, sulfonamides, co-trimoxazole or formulation excipients
• Severe hepatic impairment
• Severe renal insufficiency when repeated plasma-concentration measurement is unavailable
• Previous trimethoprim- or sulfonamide-induced immune thrombocytopenia
• Acute porphyria
• Infants during the first six weeks of life
• First trimester of pregnancy
• Previous SJS, TEN, DRESS or AGEP attributed to co-trimoxazole

Monitoring

• Renal function, fluid balance and urinary output
• Serum potassium and sodium in susceptible patients
• Full blood count during prolonged treatment and in older or folate-deficient patients
• Liver function during prolonged treatment or suspected hepatic toxicity
• Rash, fever, mucosal lesions, respiratory deterioration and unexplained bleeding
• Plasma sulfamethoxazole concentrations where required in significant renal impairment

Clinical pharmacology

The components inhibit sequential steps in microbial folate metabolism. Both distribute widely and are principally eliminated through the kidneys; renal impairment prolongs trimethoprim exposure.

Formulation and product differences

• The selected product is an intravenous solution that must be diluted.
• It is intended mainly when oral therapy is unsuitable, urgent initiation is needed or intravenous fluids are already being administered.
• It contains sodium, ethanol and propylene glycol, which may matter in young children and people with renal or hepatic impairment.
• Discard diluted solution if turbidity or crystallisation appears. Do not mix other substances into the infusion.

Solution for infusion

Route: Intravenous

Strengths: 16 mg + 80 mg/mL