Septran (co-Trimoxazole)

# Septran (co-Trimoxazole) ## Overview Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole in a fixed ratio of 1:5. It is a broad-spectrum antimicrobial agent. ## Primary Indications * **Urinary Tract Infections (UTIs):** Uncomplicated and complicated. * **Pneumocystis jirovecii pneumonia (PCP):** Treatment and prophylaxis. * **Bacterial infections:** Such as acute otitis media, acute exacerbations of chronic bronchitis, and traveler's diarrhea. Specific indications and durations vary. ## Adult Dosing * **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 3 days. * **Complicated UTIs:** 1 DS tablet every 12 hours for 7-14 days. * **PCP Treatment:** 2 DS tablets every 6 hours for 14-21 days. * **PCP Prophylaxis:** 1 DS tablet once daily, or 1 DS tablet three times weekly. Dosing frequency depends on local protocol and patient risk. * **Other Infections:** Dosing varies by indication and severity. Typical adult dose is 1 DS tablet every 12 hours. * **Maximum Daily Dose:** Generally 4 DS tablets (640 mg trimethoprim/3200 mg sulfamethoxazole) per day, unless treating severe PCP. ## Pediatric Dosing Pediatric dosing is based on trimethoprim component (usually 8 mg/kg/day) divided into two doses. Sulfamethoxazole dose is adjusted to maintain the 1:5 ratio. * **UTIs/PCP Prophylaxis:** 4 mg/kg/day trimethoprim and 20 mg/kg/day sulfamethoxazole, divided every 12 hours. This approximates 1/2 DS tablet per 15 kg body weight every 12 hours. * **PCP Treatment:** 15 mg/kg/day trimethoprim and 75 mg/kg/day sulfamethoxazole, divided every 6 hours. * **Maximum Pediatric Dose:** Generally 320 mg trimethoprim and 1600 mg sulfamethoxazole (2 DS tablets) per day. Higher doses may be used for severe PCP under expert guidance. * **Infants under 2 months:** Contraindicated due to risk of kernicterus. ## Dose Adjustments * **Renal Impairment:** * CrCl > 30 mL/min: No adjustment needed. * CrCl 15-30 mL/min: Half the usual maintenance dose. * CrCl < 15 mL/min: Avoid use; if unavoidable, use one-quarter the usual maintenance dose and monitor serum levels closely. * **Hepatic Impairment:** Use with caution. ## Contraindications * Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides. * Documented megaloblastic anemia due to folate deficiency. * Infants less than 2 months of age. * Severe renal insufficiency (CrCl < 15 mL/min) when pharmacokinetic monitoring is not feasible. * History of drug-induced immune thrombocytopenia with prior use of trimethoprim or sulfonamides. ## Adverse Effects * **Hematologic:** Megaloblastic anemia, leukopenia, thrombocytopenia, aplastic anemia. * **Dermatologic:** Rash (common, can be severe, including Stevens-Johnson syndrome and toxic epidermal necrolysis), photosensitivity. * **Gastrointestinal:** Nausea, vomiting, diarrhea, anorexia. * **Renal:** Crystalluria (ensure adequate fluid intake). * **Hepatic:** Elevated liver enzymes, hepatitis. * **Other:** Hyperkalemia, headache, dizziness, fever. ## Key Drug Interactions * **Warfarin:** Increased INR. Monitor INR closely. * **Methotrexate:** Increased risk of bone marrow suppression. * **ACE inhibitors and ARBs:** Increased risk of hyperkalemia. * **Diuretics (especially thiazides):** Increased risk of thrombocytopenia, particularly in elderly patients. * **Potassium-sparing diuretics:** Increased risk of hyperkalemia. * **Digoxin:** May increase digoxin levels. * **Cyclosporine:** May increase cyclosporine levels. * **Phenytoin:** May inhibit phenytoin metabolism. * **Sulfonylureas:** Potentiated hypoglycemic effect. ## Monitoring * **Renal function:** Especially in patients with pre-existing renal disease or those receiving concurrent nephrotoxic agents. * **Complete blood count (CBC) with differential:** Baseline and periodically, especially with prolonged therapy or in immunocompromised patients. * **Electrolytes:** Particularly potassium. * **Liver function tests:** Periodically. * **Fluid intake:** Ensure adequate hydration to prevent crystalluria. * **INR:** If co-administered with warfarin. ## Clinical Pearls * Ensure adequate fluid intake to prevent crystalluria and renal damage. * Advise patients to report any rash, sore throat, or unusual bleeding/bruising immediately. * Photosensitivity is common; advise patients to use sun protection. * Use with caution in elderly patients and those with G6PD deficiency. * Dosing for specific indications and durations may vary based on local antibiograms and clinical guidelines. *** *This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making therapeutic decisions.*