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# Septran (Co-trimoxazole) ## Overview Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole in a fixed ratio of 1:5. It inhibits sequential steps in the bacterial folic acid synthesis pathway. Available as oral tablets, oral suspension, and intravenous solution. ## Primary Indications * **Urinary Tract Infections (UTIs):** Uncomplicated cystitis, prophylaxis for recurrent UTIs. * **Pneumocystis jirovecii Pneumonia (PJP):** Treatment and prophylaxis. * **Bacterial Gastroenteritis:** Shigellosis, traveler's diarrhea (caused by susceptible organisms). * **Otitis Media:** Acute otitis media in children. * **Bronchitis:** Acute exacerbations of chronic bronchitis. * **Nocardiosis:** Treatment. ## Adult Dosing * **UTIs (Uncomplicated):** * **Treatment:** 1 DS (double strength) tablet PO every 12 hours for 3 days. * **Prophylaxis:** 1 DS tablet PO daily or 1 regular tablet PO twice daily. * **PJP:** * **Treatment:** 15 mg/kg (trimethoprim component) per day divided into 3-4 doses IV or PO for 14-21 days. Typically given as 1-2 DS tablets PO every 6-8 hours or 15-20 mg/kg/day IV. * **Prophylaxis:** 1 DS tablet PO daily or 1 DS tablet PO three times a week. * **Shigellosis:** 1 DS tablet PO every 12 hours for 5 days. * **Other indications:** Dosing varies significantly by indication and severity. Refer to specific guidelines. ## Pediatric Dosing Dosing is based on the trimethoprim component. * **General Infections:** 8-10 mg/kg/day (trimethoprim) divided into 2 doses PO or IV. * For oral suspension (40mg TMP/200mg SMX per 5mL): 10 mL PO every 12 hours for children > 12 years. For children 6 weeks to 12 years, use calculated dose based on weight. * **PJP Treatment:** 15 mg/kg/day (trimethoprim) divided into 3-4 doses IV or PO for 14-21 days. * **PJP Prophylaxis:** 5 mg/kg/day (trimethoprim) divided into 2 doses PO, not to exceed 1 DS tablet daily. * **Otitis Media:** 8 mg/kg/day (trimethoprim) divided into 2 doses PO for 10 days. ## Dose Adjustments * **Renal Impairment:** * CrCl > 30 mL/min: No adjustment needed. * CrCl 15-30 mL/min: Reduce dose by 25-50%. * CrCl < 15 mL/min: Avoid use or use with extreme caution and monitor levels. * **Hepatic Impairment:** Use with caution; monitor liver function. ## Contraindications * Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides. * History of drug-induced immune thrombocytopenia with sulfonamides or trimethoprim. * Megaloblastic anemia due to folate deficiency. * Infants less than 2 months old (risk of kernicterus). * Severe renal insufficiency where plasma concentrations cannot be monitored. * Severe hepatic insufficiency. ## Adverse Effects * **Hematologic:** Thrombocytopenia, leukopenia, neutropenia, aplastic anemia, eosinophilia. * **Dermatologic:** Rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis), photosensitivity. * **Gastrointestinal:** Nausea, vomiting, diarrhea, stomatitis. * **Hepatic:** Elevated liver enzymes, hepatitis, cholestatic jaundice. * **Renal:** Increased serum creatinine, interstitial nephritis. * **Metabolic:** Hyperkalemia, hyponatremia. * **Other:** Headache, dizziness, fever, candidiasis. ## Key Drug Interactions * **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia. * **Warfarin:** Increased INR; monitor INR closely. * **Methotrexate:** Increased methotrexate toxicity (especially with trimethoprim); co-administration generally avoided. * **Sulfonylureas:** Enhanced hypoglycemic effect; monitor blood glucose. * **Cyclosporine:** Increased cyclosporine levels, potential nephrotoxicity. * **Digoxin:** Increased digoxin levels, especially in patients with renal impairment. * **Potassium Supplements:** Increased risk of hyperkalemia. ## Monitoring * Complete blood counts (CBC) with differential, especially in prolonged therapy, elderly, or immunocompromised patients. * Renal function (BUN, creatinine). * Electrolytes (especially potassium). * Liver function tests. * Therapeutic drug monitoring may be considered in specific situations (e.g., PJP treatment in immunocompromised patients). ## Clinical Pearls * Ensure adequate hydration to minimize risk of crystalluria. * Photosensitivity is common; advise patients to use sun protection. * Discontinue immediately at the first sign of rash. * Use with caution in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. * Can interfere with urine glucose and protein tests. *** **Disclaimer:** This information is for educational purposes and is not a substitute for professional medical advice. Always consult with a qualified healthcare provider to ensure the appropriateness of any medication for a specific patient and to verify current prescribing information, including dosing, contraindications, and warnings.