Septran%25252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252520%25252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252528co-Trimoxazole%25252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252525252529

# Co-trimoxazole (Septran) ## Overview Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis. It is available in various formulations including oral tablets and intravenous solutions. ## Primary Indications * **Urinary Tract Infections (UTIs):** Uncomplicated and complicated UTIs caused by susceptible organisms. * **Pneumocystis jirovecii Pneumonia (PJP):** Treatment and prophylaxis. * **Traveler's Diarrhea:** Treatment of diarrhea caused by enterotoxigenic *Escherichia coli*. * **Other Infections:** Used for infections caused by susceptible strains of *Staphylococcus aureus*, *Haemophilus influenzae*, *Streptococcus pneumoniae*, and others, as per local antibiograms. ## Adult Dosing * **Urinary Tract Infections (Uncomplicated):** * **Treatment:** 1 DS (double strength) tablet PO every 12 hours for 3-7 days. * **Prophylaxis:** 1 DS tablet PO daily or every other day. * **Pneumocystis jirovecii Pneumonia (PJP):** * **Treatment:** 15 mg/kg/day (trimethoprim component) divided into 3-4 doses, given IV or PO for 14-21 days. Alternatively, 2 DS tablets PO every 8 hours. * **Prophylaxis:** 1 DS tablet PO daily or 1 DS tablet PO three times weekly. * **Traveler's Diarrhea:** 1 DS tablet PO every 12 hours for 3-5 days. Standard formulations include single strength (SS) tablets containing 80 mg trimethoprim and 400 mg sulfamethoxazole, and double strength (DS) tablets containing 160 mg trimethoprim and 800 mg sulfamethoxazole. IV formulations are typically 80 mg trimethoprim and 400 mg sulfamethoxazole per 5 mL. ## Pediatric Dosing Dosing is based on the trimethoprim component, calculated per kg. * **Urinary Tract Infections:** 8-10 mg/kg/day of trimethoprim component, divided into two doses, given PO or IV. * **Pneumocystis jirovecii Pneumonia (PJP):** * **Treatment:** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, given IV or PO for 14-21 days. * **Prophylaxis:** 5-7.5 mg/kg/day of trimethoprim component, divided into two doses, given PO. ## Dose Adjustments * **Renal Impairment:** * CrCl > 30 mL/min: No adjustment needed. * CrCl 15-30 mL/min: Reduce maintenance dose by 25-50%. * CrCl < 15 mL/min: Avoid use or use with extreme caution and monitor closely. ## Contraindications * Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides. * Megaloblastic anemia due to folate deficiency. * Infants less than 2 months of age (risk of kernicterus). * Severe renal or hepatic insufficiency. * History of drug-induced immune thrombocytopenia with a sulfonamide or trimethoprim. ## Adverse Effects * **Hematologic:** Agranulocytosis, aplastic anemia, megaloblastic anemia, thrombocytopenia, leukopenia. * **Dermatologic:** Stevens-Johnson syndrome, toxic epidermal necrolysis, rash, photosensitivity. * **Gastrointestinal:** Nausea, vomiting, diarrhea, anorexia. * **Hepatic:** Hepatotoxicity, elevated liver enzymes. * **Renal:** Crystalluria (ensure adequate hydration), interstitial nephritis. * **Other:** Hyperkalemia (especially with renal impairment or ACE inhibitors/ARBs), headache, dizziness, fever. ## Key Drug Interactions * **Warfarin:** Increased anticoagulant effect. Monitor INR closely. * **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Increased risk of hyperkalemia. * **ACE inhibitors and ARBs:** Increased risk of hyperkalemia. * **Methotrexate:** Increased risk of bone marrow suppression. * **Cyclosporine:** Increased cyclosporine levels. * **Potassium supplements:** Increased risk of hyperkalemia. * **Dapsone:** Increased risk of methemoglobinemia and hemolysis. * **Tricyclic Antidepressants (TCAs):** May decrease efficacy of TCAs. * **Oral contraceptives:** May decrease efficacy. ## Monitoring * **Renal function:** Baseline and periodically, especially in patients with renal impairment. * **Complete blood count (CBC) with differential:** Baseline and periodically, especially with prolonged therapy or in immunocompromised patients. * **Liver function tests:** Baseline and periodically. * **Electrolytes:** Especially potassium, particularly in patients with renal impairment or those taking other medications that affect potassium. * **Hydration status:** Advise patients to maintain adequate fluid intake to prevent crystalluria. * **Signs of hypersensitivity reactions:** Educate patients on reporting rash, fever, or other signs promptly. ## Clinical Pearls * Co-trimoxazole is effective against a broad spectrum of bacteria but resistance is increasing. Always consult local antibiograms. * Adequate hydration is crucial to prevent crystalluria. * Photosensitivity is a common adverse effect; advise patients to use sun protection. * Use with caution in patients with G6PD deficiency, as hemolytic anemia can occur. * Discontinue at the first sign of rash or severe skin reaction. *** *Disclaimer: This information is intended for clinical use and does not replace comprehensive drug information resources. Always consult the most current prescribing information and relevant guidelines before making clinical decisions.*