Indications: drug of choice in : prophylaxis and treatment of Pneumocystis jiroveci (Pneumocystis carinii) pneumonia. it is also indicated for nocardiasis, Stenotrophomonasmaltophilia infection and toxoplasmosis. It should only be considered for use in acute exacerbations of chronic bronchitis and infections of the urinary tract when there is bacteriological evidence of sensitivity to co-trimoxazole and good reason to prefer this combination to a single antibacterial: similarly it should only be used in acute otitis media in children when there is good reason to prefer it. Co-trimoxazole is also used for the treatment of infections caused by Burkholderiacepacia.

Cautions: maintain adequate fluid intake, avoid in blood disorders (unless under specialist supervision), monitor blood counts on prolonged treatment, discontinue immediately if blood disorders or rash develop, predisposition to folate deficiency or hyperkalaemia elderly, asthma, G6PD deficiency avoid in infants under 6 weeks (except for treatment or prophylaxis of pneumocystis pneumonia).

Contra-indications: acute porphyria

Hepatic impairment: manufacturer advises avoid in severe liver disease

Renal impairment: use half normal dose if eGFR 15–30 ml/minute/1.73 m2, avoid if eGFR less than 15 ml/minute/1.73 m2 and if plasma-sulfamethoxazole concentration cannot be monitored.

Pregnancy: teratogenic risk in first trimester (trimethoprim a folate antagonist). Neonatal haemolysis and methaemoglobinaemia in third trimester, fear of increased risk of kernicterus in neonates appears to be unfounded.

Breast-feeding: small risk of kernicterus in jaundiced infants and of haemolysis in G6PD-deficient infants (due to sulfamethoxazole).

Side Effects: Most common: nausea, diarrhoea; headache; hyperkalaemia; rash (very rarely including Stevens-Johnson syndrome, toxic epidermal necrolysis, photosensitivity)—discontinue immediately. less commonly: vomiting. very rarely: glossitis, stomatitis, anorexia, liver damage (including jaundice and hepatic necrosis), pancreatitis, antibiotic-associated colitis, myocarditis, cough and shortness of breath, pulmonary infiltrates, aseptic meningitis, depression, convulsions, peripheral neuropathy, ataxia, tinnitus, vertigo,

hallucinations, hypoglycaemia, blood disorders (including

leucopenia, thrombocytopenia, megaloblasticanaemia, eosinophilia), hyponatraemia, renal disorders including interstitial nephritis, arthralgia, myalgia, vasculitis, systemic lupus erythematosus and uveitis; rhabdomyolysis reported in HIV-infected patients.

Dose: By oral

Adult: 960 mg every 12 hours.

CHILD every 12 hours 6 weeks–5 months 120 mg 6 months–5 years 240 mg 6–12 years 480 mg CHILD: 36 mg/kg daily in 2 divided doses increased to 54 mg/kg daily in severe infections Treatment of Pneumocystis jiroveci (Pneumocystis carinii) infections (undertaken where facilities for appropriate monitoring available by mouth or by intravenous infusion.

ADULT and CHILD over 4 weeks 120 mg/kg daily in 2–4 divided doses for 14–21 days.

Prophylaxis of Pneumocystis jiroveci (Pneumocystis carinii) infections 960 mg once daily (may be reduced to 480 mg once daily to improve tolerance) or 960 mg on alternate days (3 times a week) Or 960 mg twice daily on alternate days (3 times a week). CHILD 6 weeks–5 months 120 mg twice daily on 3 consecutive Or alternate days per week or on 7 days per week. 6 months–5 years 240 mg 6–12 years 480 mg.