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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic consisting of trimethoprim and sulfamethoxazole. It is bactericidal and works by inhibiting sequential steps in the folic acid synthesis pathway.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Certain bacterial respiratory infections (e.g., acute exacerbations of chronic bronchitis)
* Shigellosis
* Traveler's diarrhea
## Adult Dosing
* **UTIs and acute exacerbations of chronic bronchitis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days (UTI) or 10-14 days (bronchitis).
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 3-4 doses, with 75-100 mg/kg/day sulfamethoxazole component, divided into 4 doses, for 14-21 days. Maximum daily trimethoprim dose is 960 mg.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) once daily. Alternatively, 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) three times a week.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 5 days.
* **Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-5 days.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **UTIs and acute exacerbations of chronic bronchitis:** 8 mg/kg/day trimethoprim and 40 mg/kg/day sulfamethoxazole, divided into two equally divided doses every 12 hours. Maximum daily trimethoprim dose is 320 mg.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim and 75-100 mg/kg/day sulfamethoxazole, divided into 3-4 doses every 6-8 hours for 14-21 days.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim and 25 mg/kg/day sulfamethoxazole, divided into two equally divided doses daily. Alternatively, 10 mg/kg/day trimethoprim and 50 mg/kg/day sulfamethoxazole, divided into two equally divided doses, given 3 times a week.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfamethoxazole.
* History of drug-induced immune thrombocytopenia with the use of sulfonamides or trimethoprim.
* Megaloblastic anemia due to folate deficiency.
* Premature infants and infants up to 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency when functional tests cannot be performed.
## Adverse Effects
* **Common:** Rash (can be severe, including Stevens-Johnson syndrome/toxic epidermal necrolysis), pruritus, nausea, vomiting, diarrhea.
* **Hematologic:** Leukopenia, neutropenia, thrombocytopenia, megaloblastic anemia, eosinophilia, aplastic anemia.
* **Hepatic:** Elevated transaminases, cholestatic jaundice.
* **Renal:** Increased serum creatinine, interstitial nephritis.
* **Other:** Hyperkalemia, hyponatremia, photosensitivity, DRESS syndrome.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and consider dose reduction of warfarin.
* **Methotrexate:** Increased methotrexate levels, leading to toxicity. Avoid concomitant use or monitor methotrexate levels closely and consider folic acid supplementation.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia. Monitor potassium levels.
* **Sulfonylureas:** Increased risk of hypoglycemia. Monitor blood glucose.
* **Cyclosporine:** Increased cyclosporine levels, potential for nephrotoxicity. Monitor cyclosporine levels and renal function.
* **Digoxin:** Increased digoxin levels. Monitor digoxin levels.
* **Indomethacin:** Increased sulfonamide levels.
## Monitoring
* Complete blood counts (CBC) with differential and platelet count, especially with prolonged therapy or in patients with G6PD deficiency.
* Renal and liver function tests.
* Electrolytes (especially potassium).
* Signs and symptoms of hypersensitivity reactions.
* INR if on warfarin.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Photosensitivity is a common side effect; advise patients to use sun protection.
* Discontinue immediately if a rash develops, as it can be a sign of serious skin reactions.
* Consider folic acid supplementation (5 mg daily) during prolonged therapy, especially in elderly patients or those with folate deficiency, to reduce the risk of hematologic side effects.
* Septra suspension contains phenylalanine and should be avoided in patients with phenylketonuria.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional guidelines before making clinical decisions.*
