India · TMP-SMX · Paediatric mg/kg · Adult · UTI · PCP Prophylaxis · HIV · Septran · Bactrim · Enteroquinol
CrCl ≥ 30: Standard dose
CrCl 15–30: Half the standard dose
CrCl < 15: Avoid — risk of crystalluria and toxicity
⚠️ Ensure adequate hydration (2L/day) to reduce crystalluria risk at any CrCl
| Indication | Paediatric dose (TMP component) | Adult dose (total cotrimoxazole) | Duration |
|---|---|---|---|
| UTI (uncomplicated, woman) | 4 mg TMP/kg BD | 960mg (1 DS tab) BD | 3 days |
| UTI (complicated / man) | 4 mg TMP/kg BD | 960mg BD | 7–10 days |
| UTI prophylaxis (recurrent) | 2 mg TMP/kg OD | 480mg (1 SS tab) OD at bedtime | 6–12 months |
| PCP prophylaxis (HIV adult) | — | 960mg (1 DS tab) OD | Until CD4 >200 on 2 consecutive counts |
| PCP prophylaxis (child HIV) | 5 mg TMP/kg OD (or 150mg TMP/m²/day) | — | Until HIV excluded or ART criteria met |
| PCP treatment (moderate) | 15–20 mg TMP/kg/day in 3–4 doses | TMP 15–20 mg/kg/day in 3–4 doses (high dose) | 21 days (+ prednisolone if PaO2 <70) |
| Toxoplasmosis prophylaxis (HIV) | — | 960mg OD (same as PCP) | Ongoing until CD4 >200 |
| Nocardia infection | — | 960mg BD–TDS (high dose, prolonged) | 6–12 months (specialist directed) |
Cotrimoxazole (trimethoprim-sulfamethoxazole, TMP-SMX) is a combination antibiotic that blocks two consecutive steps in bacterial folate synthesis — trimethoprim inhibits dihydrofolate reductase, and sulfamethoxazole inhibits dihydropteroate synthase. The synergistic combination achieves bactericidal activity against many Gram-positive and Gram-negative organisms, as well as Pneumocystis jirovecii (the cause of PCP pneumonia) and Toxoplasma gondii. It is on the WHO Essential Medicines List and is a cornerstone of HIV care in India through the NACO cotrimoxazole prophylaxis programme.
Cotrimoxazole dosing guidelines (BNF, BNFC, WHO, NACO) are written in terms of the trimethoprim (TMP) component. This causes significant confusion when prescribing because Indian brands (Septran, Bactrim) state the total cotrimoxazole content on the packet. The standard adult single-strength (SS) tablet contains TMP 80mg + SMX 400mg = 480mg total. The double-strength (DS) tablet contains TMP 160mg + SMX 800mg = 960mg total. Always confirm which strength you are prescribing.
Cotrimoxazole prophylaxis (CTX) is one of the most impactful, lowest-cost interventions in HIV care. NACO India guidelines recommend initiating CTX in all HIV-infected adults when CD4 count falls below 200 cells/mm³ (or at any CD4 count if WHO clinical stage 3 or 4). Dose: cotrimoxazole 960mg (1 DS tablet) once daily. CTX also provides prophylaxis against toxoplasmosis, malaria, and bacterial infections — a single tablet providing multiple protective benefits. Discontinue when CD4 >200 cells/mm³ on two consecutive measurements 3 months apart and patient is virologically suppressed on ART.
Cotrimoxazole is predominantly renally excreted and requires dose reduction in renal impairment. For CrCl 15–30 mL/min: reduce to half the standard dose (480mg once daily instead of twice daily for UTI; 480mg instead of 960mg for PCP prophylaxis). For CrCl <15 mL/min: avoid cotrimoxazole — risk of crystalluria, hyperkalemia (TMP is potassium-sparing), and sulfonamide toxicity. Always ensure adequate hydration (2L of fluid/day) to prevent crystalluria at any level of renal function.
TMP can increase serum creatinine without truly affecting GFR (it inhibits renal tubular secretion of creatinine). Do not interpret a creatinine rise alone as CKD progression in a patient started on cotrimoxazole — check cystatin C or eGFR by CKD-EPI if concerned. TMP also raises serum potassium (like a potassium-sparing diuretic) — monitor K+ in patients on ACEi, ARBs, or those with pre-existing hyperkalaemia.