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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a fixed-dose combination of sulfamethoxazole (a sulfonamide) and trimethoprim (a dihydrofolate reductase inhibitor). It exhibits broad-spectrum antibacterial activity.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Acute otitis media
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea (enterotoxigenic E. coli)
## Adult Dosing
* **UTIs, Acute Otitis Media, Acute Exacerbations of Chronic Bronchitis:**
* 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 7-14 days.
* **PJP Treatment:**
* Higher doses are typically used. Consult specific treatment guidelines. Common regimen: 15-20 mg/kg/day trimethoprim component divided into 3-4 doses for 14-21 days.
* **PJP Prophylaxis:**
* 1 DS tablet daily or 1 DS tablet three times weekly.
* **Shigellosis:**
* 1 DS tablet every 12 hours for 5 days.
* **Traveler's Diarrhea:**
* 1 DS tablet every 12 hours for up to 5 days.
Maximum daily dose generally 4 DS tablets.
## Pediatric Dosing
Dosing is based on the trimethoprim component, typically 8 mg/kg/day divided into two doses.
* **UTIs, Acute Otitis Media:**
* 40 mg trimethoprim/200 mg sulfamethoxazole (1 regular strength tablet or 5 mL suspension) every 12 hours for 10 days.
* **PJP Prophylaxis:**
* 5 mg/kg/day trimethoprim component divided into two doses, given on 3 consecutive days per week.
* **PJP Treatment:**
* 15-20 mg/kg/day trimethoprim component divided into 3-4 doses for 14-21 days.
Note: Suspension contains 200 mg sulfamethoxazole and 40 mg trimethoprim per 5 mL.
## Dose Adjustments
* **Renal Impairment:** Dose adjustment is necessary.
* Creatinine clearance (CrCl) > 30 mL/min: Administer usual dose.
* CrCl 15-30 mL/min: Administer 1/2 to 1/3 of usual dose.
* CrCl < 15 mL/min: Contraindicated.
## Contraindications
* Documented hypersensitivity to trimethoprim or sulfonamides.
* Severe renal insufficiency (CrCl < 15 mL/min).
* Severe hepatic insufficiency.
* Megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Use in term infants during pregnancy, especially at term (risk of kernicterus).
## Adverse Effects
* **Common:** Rash, pruritus, nausea, vomiting, diarrhea.
* **Serious:** Severe dermatologic reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hypersensitivity reactions (including anaphylaxis), hematologic abnormalities (leukopenia, thrombocytopenia, aplastic anemia, megaloblastic anemia), hyperkalemia, renal failure, hepatic toxicity (including cholestatic jaundice), photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Phenytoin:** Increased phenytoin levels.
* **Sulfonylureas:** Enhanced hypoglycemic effect.
* **Thiazide diuretics:** Increased risk of thrombocytopenia, particularly in the elderly.
* **Cyclosporine:** Increased cyclosporine levels.
## Monitoring
* Renal function (BUN, creatinine).
* Complete blood counts (CBC) with differential, especially with prolonged therapy or in elderly patients.
* Electrolytes (especially potassium).
* Liver function tests.
* Signs of hypersensitivity or rash.
## Clinical Pearls
* Take with a full glass of water to prevent crystalluria.
* Maintain adequate fluid intake.
* Advise patients to report any rash, fever, sore throat, or other signs of infection.
* Use with caution in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency.
* Consider folic acid supplementation, especially with prolonged therapy, to reduce risk of hematologic effects.
***
*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for complete details and to ensure patient safety.*
