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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole. It is a bacteriostatic agent that inhibits folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Certain respiratory tract infections
* Gastrointestinal infections (e.g., Shigella)
* Otitis media
## Adult Dosing
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) orally every 12 hours for 3 days.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 3-4 doses, orally or IV, for 14-21 days.
* **PJP Prophylaxis:** 1 DS tablet orally daily or 1 DS tablet orally 3 times a week.
* **Other infections:** Dosing varies by infection type and severity, often 1-2 DS tablets orally or IV every 12 hours. Maximum dose: typically 8 DS tablets (640 mg trimethoprim/3200 mg sulfamethoxazole) per day.
## Pediatric Dosing
Dosing is based on the trimethoprim component, calculated per kg of body weight, and then adjusted for the fixed ratio of trimethoprim to sulfamethoxazole. **Specific dosing protocols should be followed as per local guidelines.**
* **General infections:** 8-10 mg/kg/day trimethoprim component, divided into 2 doses.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 3-4 doses.
* **PJP Prophylaxis:** 5-10 mg/kg/day trimethoprim component, divided into 1-2 doses.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer 75% of usual dose.
* CrCl < 15 mL/min: Avoid use or administer 50% of usual dose at extended intervals (e.g., every 24 hours). Consult product information for precise recommendations.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfamethoxazole.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (due to risk of kernicterus).
* Severe renal insufficiency where plasma concentrations cannot be monitored.
* Severe hepatic insufficiency.
## Adverse Effects
Common: Nausea, vomiting, rash, diarrhea.
Serious: Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), bone marrow suppression (anemia, leukopenia, thrombocytopenia), hyperkalemia, crystalluria, hepatic dysfunction, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels, potentially leading to toxicity.
* **Potassium supplements/Potassium-containing salt substitutes:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels, particularly in transplant patients.
* **Digoxin:** Increased digoxin levels.
## Monitoring
* **Renal function:** Especially in patients with impaired renal function.
* **Electrolytes:** Particularly potassium levels.
* **Complete blood counts (CBC):** Baseline and periodically during prolonged therapy or in immunocompromised patients.
* **Liver function tests (LFTs).**
* **Signs of hypersensitivity/skin reactions.**
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Photosensitivity can occur; advise sun protection.
* TMP/SMX can interfere with urine glucose testing and may cause false-positive results for some urine drug screens.
* Trimethoprim component may cause a reversible increase in serum creatinine without affecting glomerular filtration rate; this is a pseudo-elevated creatinine.
**Always consult current prescribing information and local protocols for definitive guidance.**
