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# Septran (Co-Trimoxazole)
## Overview
Co-trimoxazole is a combination of trimethoprim and sulfamethoxazole, a sulfonamide antibiotic. It is a broad-spectrum antibacterial agent.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea (enterotoxigenic E. coli)
* Otitis media
## Adult Dosing
Dosing is based on the trimethoprim component, typically expressed as mg of trimethoprim per mg of sulfamethoxazole. Standard strength tablets contain 80 mg trimethoprim and 400 mg sulfamethoxazole.
* **UTIs and Shigellosis:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 3-7 days (UTI) or 5 days (shigellosis).
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim divided into 3-4 doses with 75-100 mg/kg/day sulfamethoxazole.
* **PJP Prophylaxis:** 160 mg trimethoprim / 800 mg sulfamethoxazole daily or every other day.
* **Chronic Bronchitis:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 7-14 days.
* **Traveler's Diarrhea:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 3-5 days.
## Pediatric Dosing
Dosing is based on mg/kg/day of trimethoprim. The total daily dose of trimethoprim is divided into 2-4 doses.
* **UTIs:** 8 mg/kg/day trimethoprim (as the sum of both components) divided every 12 hours.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim divided into 3-4 doses with 75-100 mg/kg/day sulfamethoxazole.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim divided every 12 hours, or 150 mg/m²/day sulfamethoxazole.
* **Shigellosis:** 8 mg/kg/day trimethoprim divided every 12 hours for 5 days.
* **Otitis Media:** 8 mg/kg/day trimethoprim divided every 12 hours for 10 days.
**Note:** For pediatric use, specific formulations (e.g., suspension) are often preferred.
## Dose Adjustments
* **Renal Impairment:** Dose reduction is necessary based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: Full dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use or give one-quarter the usual dose every 12 hours.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency where urine or blood levels cannot be monitored.
* History of drug-induced thrombocytopenia with use of trimethoprim or sulfonamides.
## Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea, hyperkalemia.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), exfoliative dermatitis, anaphylaxis, hematologic abnormalities (agranulocytosis, aplastic anemia, thrombocytopenia, megaloblastic anemia), severe hepatotoxicity, hyperkalemia, crystalluria (ensure adequate hydration).
## Key Drug Interactions
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Methotrexate:** Increased risk of bone marrow suppression. Co-administration with folinic acid (leucovorin) may be necessary.
* **Cyclosporine:** Increased cyclosporine levels and nephrotoxicity.
* **Digoxin:** Increased digoxin levels.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Diuretics (Thiazide, Loop):** Increased risk of thrombocytopenia in elderly patients.
## Monitoring
* **Renal function:** Baseline and periodic monitoring, especially in patients with impaired renal function.
* **Electrolytes:** Particularly potassium, especially in patients with renal impairment or on ACE inhibitors/ARBs.
* **Complete Blood Count (CBC):** Baseline and periodic monitoring for hematologic abnormalities, especially with prolonged therapy or in immunocompromised patients.
* **Liver function tests (LFTs):** Baseline and periodic monitoring.
* **Hydration:** Advise patients to maintain adequate fluid intake to prevent crystalluria.
## Clinical Pearls
* Co-trimoxazole is a potent inducer of P-glycoprotein, which can affect the absorption and clearance of other drugs.
* Concurrent administration of folinic acid (leucovorin) can reduce the risk of hematologic toxicity, particularly in PJP prophylaxis and treatment, and in patients with impaired folate metabolism.
* Photosensitivity is a potential adverse effect; advise patients to use sun protection.
* Always use the lowest effective dose for the shortest duration necessary.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions.*
