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# Septran (Trimethoprim/Sulfamethoxazole)
## Overview
Septran is a combination antibiotic containing trimethoprim and sulfamethoxazole in a 1:5 ratio. It is a bacteriostatic agent that inhibits folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Bacterial gastroenteritis (e.g., Shigella)
* Acute otitis media (in certain situations)
* Travelers' diarrhea
* Prostatitis
## Adult Dosing
* **Urinary Tract Infections & Gastroenteritis:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 3-7 days (UTI) or 5 days (gastroenteritis).
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15 mg/kg/day trimethoprim component, divided into 3-4 doses, every 12-24 hours for 14-21 days. (e.g., 160 mg/kg/day of the combination, divided into 3-4 doses).
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 1 DS tablet (160 mg trimethoprim/800 mg sulfamethoxazole) daily, or 1 single-strength tablet (80 mg trimethoprim/400 mg sulfamethoxazole) twice daily.
* **Prostatitis:** 1 DS tablet every 12 hours for 4 weeks.
## Pediatric Dosing
Dosing is based on the trimethoprim component. **Note:** Not recommended for infants younger than 2 months due to risk of kernicterus.
* **Urinary Tract Infections:** 8 mg/kg/day trimethoprim component, divided into 2 doses, given every 12 hours. This equates to approximately 20 mg/kg/day of the combination, divided every 12 hours.
* For children 6-12 years: 1 single-strength tablet (80 mg trimethoprim/400 mg sulfamethoxazole) twice daily.
* For children >12 years: Adult dosing applies.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15 mg/kg/day trimethoprim component, divided into 3-4 doses, every 12-24 hours for 14-21 days.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 5 mg/kg/day trimethoprim component, divided into 2 doses, given every 12 hours.
## Dose Adjustments
* **Renal Impairment:**
* CrCl >30 mL/min: Full dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl <15 mL/min: Avoid use or administer only after careful consideration of benefits and risks, with monitoring.
## Contraindications
* Hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants younger than 2 months.
* Severe renal or hepatic insufficiency.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
## Adverse Effects
* **Common:** Nausea, vomiting, rash (especially in HIV patients).
* **Serious:**
* Hematologic: Aplastic anemia, agranulocytosis, thrombocytopenia, leukopenia, megaloblastic anemia (can be exacerbated by folate deficiency).
* Dermatologic: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), exfoliative dermatitis.
* Hepatic: Elevated liver enzymes, hepatitis, cholestatic jaundice.
* Renal: Crystalluria (ensure adequate fluid intake), elevated BUN/creatinine.
* Electrolyte: Hyperkalemia.
* Hypersensitivity reactions.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased risk of bone marrow suppression.
* **Digoxin:** Increased digoxin levels.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels, potential for nephrotoxicity.
* **Oral Contraceptives:** Potential for reduced efficacy.
## Monitoring
* Complete blood counts (CBC) with differential periodically, especially during prolonged therapy or in patients with G6PD deficiency.
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium).
* Liver function tests.
* Signs and symptoms of hypersensitivity reactions.
* INR in patients taking warfarin.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Rash is common and can be a sign of serious hypersensitivity; advise patients to report any rash immediately.
* Sulfonamides can cause photosensitivity; advise sun protection.
* Monitor for signs of bone marrow suppression, especially in elderly patients or those with folate deficiency.
* Consider folate supplementation (1 mg daily) in patients on prolonged therapy, especially those at risk for folate deficiency.
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**Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant literature, and exercise clinical judgment when making treatment decisions. Dosing may vary based on specific clinical situations and local protocols.
