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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic containing trimethoprim and sulfamethoxazole in a fixed ratio of 1:5. It inhibits bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Bacterial respiratory tract infections
* Gastrointestinal infections (e.g., traveler's diarrhea)
* Otitis media
## Adult Dosing
* **UTIs and most bacterial infections:** 1 double-strength (DS) tablet (800 mg sulfamethoxazole/160 mg trimethoprim) every 12 hours. For severe infections, 1.5 DS tablets every 12 hours.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component, divided into 3-4 doses, given orally or IV. This typically equates to 2 DS tablets every 8 hours for 14-21 days.
* **PJP Prophylaxis:** 1 DS tablet once daily, or 1 DS tablet three times weekly.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **UTIs and most bacterial infections:** 8 mg/kg/day of trimethoprim, divided into two doses every 12 hours. Total daily dose should not exceed 320 mg of trimethoprim (equivalent to 2 DS tablets).
* **PJP Treatment:** 15 mg/kg/day of trimethoprim, divided into 3-4 doses every 6-8 hours for 14-21 days.
* **PJP Prophylaxis:** 5 mg/kg/day of trimethoprim, divided into two doses every 12 hours, given daily or on alternate days. Maximum daily dose 160 mg trimethoprim.
**Note:** For pediatric suspensions, reconstitute and shake well. Usual concentrations are 200 mg sulfamethoxazole/40 mg trimethoprim per 5 mL.
## Dose Adjustments
* **Renal Impairment (CrCl mL/min):**
* CrCl > 30: No adjustment needed.
* CrCl 15-30: Administer 75% of the usual dose.
* CrCl < 15: Avoid use. If use is unavoidable, administer 50% of the usual dose every 12 hours.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or other sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic impairment.
* History of drug-induced thrombocytopenia with the use of trimethoprim or sulfonamides.
## Adverse Effects
Common: Nausea, vomiting, rash (may be severe, including Stevens-Johnson syndrome and toxic epidermal necrolysis), diarrhea, anorexia, headache.
Less Common: Hyperkalemia, hyponatremia, dizziness, leukopenia, eosinophilia, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate toxicity (may be due to displacement from plasma protein binding or inhibition of renal excretion).
* **Cyclosporine:** Increased cyclosporine levels, especially in transplant recipients.
* **Digoxin:** Increased digoxin levels.
* **Potassium supplements and Potassium-containing salt substitutes:** Increased risk of hyperkalemia.
* **Thiazide diuretics:** Increased risk of thrombocytopenia in elderly patients.
## Monitoring
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium and sodium).
* Complete blood counts (CBC) with differential, particularly with prolonged therapy or in patients with G6PD deficiency or folate deficiency.
* Liver function tests.
* INR if co-administered with warfarin.
* Signs of hypersensitivity reactions.
## Clinical Pearls
* Administer with food or milk to minimize gastrointestinal upset.
* Encourage adequate fluid intake to prevent crystalluria.
* Sulfonamides can cause crystalluria; monitor urine pH and consider alkalinization if needed.
* Photosensitivity is common; advise patients to use sun protection.
* The risk of severe skin reactions is higher in patients with sulfa allergies.
* In PJP treatment, monitor for worsening respiratory status and eosinophilia.
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*Disclaimer: This information is intended for clinical use and does not substitute for comprehensive drug information resources. Always verify current prescribing information and consult appropriate resources before making clinical decisions.*
