Co-trimoxazole

What it is and how it works

Co-trimoxazole combines sulfamethoxazole and trimethoprim in a 5:1 ratio. Sulfamethoxazole inhibits bacterial dihydropteroate synthase and trimethoprim inhibits dihydrofolate reductase, producing sequential blockade of folate synthesis that is often bactericidal.

Indications

Treatment and prophylaxis of Pneumocystis jirovecii pneumonia, toxoplasmosis and nocardiasis; urinary tract infections and acute exacerbations of chronic bronchitis where there is good bacteriological reason to prefer it.

Dosage and administration (summary)

Adults, oral: usually 960 mg every 12 hours. Intravenous infusion (after dilution): usually 960 mg every 12 hours, increased in severe infection; for Pneumocystis pneumonia 120 mg/kg daily in 2–4 divided doses. Dose reduction is required in renal impairment.

Contraindications

Hypersensitivity to sulfonamides or trimethoprim; severe hepatic impairment, severe renal impairment where plasma concentrations cannot be monitored, acute porphyria, and neonates (risk of kernicterus).

Warnings and precautions

Can cause severe cutaneous reactions (Stevens–Johnson syndrome, toxic epidermal necrolysis) and blood dyscrasias; stop at the first appearance of rash. Hyperkalaemia and folate deficiency may occur, particularly in the elderly, in renal impairment and at high doses; blood counts should be monitored during prolonged treatment.

Pregnancy

Avoid in the first trimester because of folate antagonism, and near term because of the risk of neonatal haemolysis and kernicterus.

Storage and supply

Store below 25 °C, protected from light; do not refrigerate the concentrate for infusion.

Source: reference summary prepared from the EU SmPC/EPAR, BNF and WHO Model Formulary. The approved product information in Iran governs.