Septran%2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252520%2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252528co-Trimoxazole%2525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252529

# Septran (Co-Trimoxazole) ## Overview Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole, which act synergistically to inhibit bacterial folate synthesis. ## Primary Indications * **Urinary Tract Infections (UTIs)**: Uncomplicated and complicated UTIs. * **Pneumocystis jirovecii Pneumonia (PJP)**: Treatment and prophylaxis. * **Bacterial Gastroenteritis**: Including Shigella and traveler's diarrhea. * **Otitis Media**: In children. * **Bronchitis**: Acute exacerbations. * **Prophylaxis**: Against PJP in immunocompromised individuals. ## Adult Dosing * **UTIs**: 160 mg trimethoprim / 800 mg sulfamethoxazole (one double-strength tablet) every 12 hours for 3-7 days for uncomplicated UTIs. For complicated UTIs, duration may be extended. * **PJP Treatment**: 15-20 mg/kg/day of trimethoprim component, given in 3-4 divided doses, for 14-21 days. * **PJP Prophylaxis**: 160 mg trimethoprim / 800 mg sulfamethoxazole daily or 160 mg trimethoprim / 800 mg sulfamethoxazole three times weekly. * **Bacterial Gastroenteritis**: 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 3-5 days. *Maximum daily dose generally should not exceed 960 mg trimethoprim / 4800 mg sulfamethoxazole (6 double-strength tablets).* ## Pediatric Dosing Pediatric dosing is typically based on the trimethoprim component, with the ratio of trimethoprim to sulfamethoxazole being 1:5. * **General Infections (e.g., UTIs, Otitis Media)**: 8 mg/kg/day of trimethoprim component divided into two doses (e.g., 40 mg/kg/day of sulfamethoxazole component). For example, a 20 kg child would receive approximately 160 mg trimethoprim / 800 mg sulfamethoxazole daily. * **PJP Treatment**: 15-20 mg/kg/day of trimethoprim component, given in 3-4 divided doses, for 14-21 days. * **PJP Prophylaxis**: 150 mg/m² of trimethoprim component and 750 mg/m² of sulfamethoxazole component per day, given in two divided doses on 3 consecutive days a week (e.g., Friday, Saturday, Sunday). *Use in infants < 2 months is generally avoided due to risk of kernicterus.* ## Dose Adjustments * **Renal Impairment**: * CrCl > 30 mL/min: No adjustment needed. * CrCl 15-30 mL/min: Reduce dose by 50%. * CrCl < 15 mL/min: Avoid use. * **Hepatic Impairment**: Use with caution, monitor liver function. ## Contraindications * Known hypersensitivity to trimethoprim, sulfamethoxazole, or other sulfonamides. * Documented megaloblastic anemia due to folate deficiency. * Infants < 2 months of age. * Severe renal or hepatic insufficiency when frequent monitoring is not possible. ## Adverse Effects * **Hematologic**: Megaloblastic anemia, leukopenia, thrombocytopenia, aplastic anemia, agranulocytosis. * **Dermatologic**: Rash (common, can be severe, Stevens-Johnson syndrome, toxic epidermal necrolysis), photosensitivity. * **Gastrointestinal**: Nausea, vomiting, diarrhea, anorexia. * **Hepatic**: Elevated liver enzymes, hepatitis, cholestatic jaundice. * **Renal**: Crystalluria (ensure adequate hydration). * **Other**: Hyperkalemia, dizziness, headache. ## Key Drug Interactions * **Warfarin**: Increased INR; monitor INR closely. * **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics**: Increased risk of hyperkalemia. * **Methotrexate**: May increase methotrexate levels and toxicity. * **Potassium Supplements**: Increased risk of hyperkalemia. * **Dapsone**: Increased levels of both agents. * **Cyclosporine**: Increased cyclosporine levels, particularly in transplant patients. * **Oral Hypoglycemics**: May potentiate hypoglycemic effects. * **Rifampicin**: May decrease co-trimoxazole levels and vice versa. ## Monitoring * **Renal function (CrCl, BUN, creatinine)**, especially with impaired renal function or concurrent nephrotoxic agents. * **Complete Blood Count (CBC)** with differential and platelet count: Baseline and periodically during prolonged therapy or in high-risk patients. * **Electrolytes (especially potassium)**. * **Liver function tests**. * **Hydration status** to prevent crystalluria. * **INR** in patients taking warfarin. ## Clinical Pearls * Ensure adequate fluid intake to prevent crystalluria, especially with higher doses or in patients with renal impairment. * Advise patients to report any rash, sore throat, or fever immediately, as these could be signs of serious hypersensitivity reactions. * Co-trimoxazole is a common cause of drug-induced rash. * Consider folic acid supplementation (5-10 mg daily) during prolonged treatment courses, especially in elderly patients, pregnant women, or those with folate deficiency, to mitigate hematologic side effects. * Co-trimoxazole is a P450 inhibitor, though clinical significance is variable. **Disclaimer**: Always consult the most current prescribing information and institutional guidelines for definitive dosing and management.