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# Septran (co-trimoxazole)
## Overview
Septran is a combination of sulfamethoxazole and trimethoprim, a sulfonamide and dihydrofolate reductase inhibitor, respectively. It exhibits bacteriostatic and bactericidal activity against a broad spectrum of bacteria.
## Primary Indications
* Treatment of urinary tract infections (UTIs) due to susceptible organisms.
* Treatment of acute otitis media due to susceptible organisms.
* Treatment and prophylaxis of *Pneumocystis jirovecii* pneumonia (PJP).
* Treatment of traveler's diarrhea.
* Treatment of shigellosis.
## Adult Dosing
* **UTIs and Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days for UTIs, or 3-5 days for traveler's diarrhea.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 5 days.
* **PJP Treatment:** 15 mg/kg/day trimethoprim component, divided into 3 or 4 doses, administered orally or IV. The sulfamethoxazole component is typically dosed at 75 mg/kg/day. Duration is typically 14-21 days.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) daily, or 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) three times weekly.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **UTIs and Acute Otitis Media:** 8 mg/kg/day trimethoprim component, divided into two doses, administered every 12 hours. For children older than 2 months.
* **PJP Treatment:** 15 mg/kg/day trimethoprim component, divided into 3 or 4 doses, administered orally or IV. The sulfamethoxazole component is typically dosed at 75 mg/kg/day. Duration is typically 14-21 days.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim component, divided into two doses, administered every 12 hours, or 150 mg/m²/day sulfamethoxazole component divided into two doses. Maximum daily trimethoprim dose 320 mg.
## Dose Adjustments
* **Renal Impairment:** Adjust dose based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: Full dose.
* CrCl 15-30 mL/min: Half the usual recommended dose every 12 hours.
* CrCl < 15 mL/min: Contraindicated.
## Contraindications
* Documented hypersensitivity to trimethoprim, sulfamethoxazole, or other sulfonamides.
* Diagnosis of severe megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Marked liver parenchymal damage.
* Anuria.
## Adverse Effects
Common: Nausea, vomiting, rash, pruritus, hyperkalemia.
Serious: Stevens-Johnson syndrome, toxic epidermal necrolysis, severe cutaneous adverse reactions (SCARs), aplastic anemia, agranulocytosis, thrombocytopenia, leukopenia, hyperkalemia, hyponatremia, hepatotoxicity, renal impairment, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and consider dose adjustment of warfarin.
* **ACE inhibitors and ARBs:** Increased risk of hyperkalemia. Monitor potassium levels.
* **Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased risk of methotrexate toxicity. Concomitant use with folic acid may be considered.
* **Digoxin:** Increased digoxin levels. Monitor digoxin levels.
* **Cyclosporine:** Increased cyclosporine levels, particularly in renal transplant patients.
## Monitoring
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium).
* Complete blood counts (CBC) with differential and platelet count, especially with prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs) if indicated.
* For PJP treatment, monitor for signs of clinical improvement.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Advise patients to report any skin rash, fever, sore throat, or jaundice immediately.
* Photosensitivity can occur; advise sun protection.
* Co-trimoxazole can interfere with certain laboratory tests (e.g., serum creatinine when using the Jaffé method).
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always verify current prescribing information with the official drug labeling and consult with a healthcare provider for specific patient care decisions.
