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# Septran (Co-Trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Shigellosis
* Acute otitis media (AOM)
* Traveler's diarrhea (caused by susceptible organisms)
## Adult Dosing
Dosing is typically based on the trimethoprim component. Standard dose: 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours.
* **UTI:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 3-7 days.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim divided into 3-4 doses for 14-21 days.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole once daily or 80 mg trimethoprim/400 mg sulfamethoxazole twice daily.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 5 days.
* **Traveler's diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 3-5 days.
## Pediatric Dosing
Dosing is based on trimethoprim component, calculated as mg/kg/day.
* **UTI/Shigellosis:** 8-10 mg/kg/day trimethoprim divided into two doses.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim divided into 3-4 doses for 14-21 days.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim divided into two doses.
Maximum pediatric dose usually not to exceed the adult dose.
## Dose Adjustments
**Renal Impairment (CrCl):**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Half of the usual dose.
* CrCl < 15 mL/min: Avoid use or give one-fourth of the usual dose.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency when functional tests are unavailable.
## Adverse Effects
Common: Rash, nausea, vomiting, diarrhea, pruritus.
Serious: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), exfoliative dermatitis, severe hypersensitivity reactions, blood dyscrasias (anemia, thrombocytopenia, leukopenia, agranulocytosis), hyperkalemia, renal failure, hepatotoxicity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Potassium-sparing diuretics (e.g., spironolactone):** Increased risk of hyperkalemia.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased nephrotoxicity.
* **Digoxin:** Increased digoxin levels.
* **Phenytoin:** Increased phenytoin levels.
## Monitoring
* Renal function (BUN, creatinine)
* Electrolytes (especially potassium)
* Complete blood count (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs)
* Signs of hypersensitivity reactions.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Monitor for signs of rash and discontinue if a severe rash develops.
* Sulfonamides are structurally related to sulfonylureas; caution in diabetic patients.
* Consider folate supplementation in patients receiving long-term therapy or those at risk for folate deficiency.
* Avoid use in patients with G6PD deficiency due to risk of hemolytic anemia.
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*This information is intended for educational purposes and does not substitute for professional medical advice. Always consult the most current prescribing information and relevant guidelines for definitive patient care decisions.*
