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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic containing sulfamethoxazole and trimethoprim, which work synergistically to inhibit bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Certain respiratory tract infections
* Certain gastrointestinal infections
## Adult Dosing
Dosing varies significantly based on indication.
* **UTIs:** Typically 1 double-strength (DS) tablet (800 mg sulfamethoxazole/160 mg trimethoprim) every 12 hours for 3-14 days.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses IV or PO for 14-21 days.
* **PCP Prophylaxis:** 1 DS tablet (800 mg sulfamethoxazole/160 mg trimethoprim) PO daily or 1 DS tablet PO 3 times weekly.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **General Infections:** 8-10 mg/kg/day trimethoprim component divided into 2 doses PO or IV.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses IV or PO for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim component PO divided into 2 doses daily, or 150 mg/m²/day trimethoprim component PO divided into 3 doses daily.
**Note:** Actual pediatric dosing often depends on specific institutional protocols and severity of infection.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment.
* CrCl 15-30 mL/min: Give 75% of usual dose.
* CrCl < 15 mL/min: Avoid use or give 50% of usual dose every 12 hours.
## Contraindications
* Hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Premature infants and infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency when plasma concentrations cannot be monitored.
* History of drug-induced thrombocytopenia with either component.
## Adverse Effects
Common: Nausea, vomiting, rash, hyperkalemia.
Serious: Stevens-Johnson syndrome, toxic epidermal necrolysis, blood dyscrasias (agranulocytosis, aplastic anemia, thrombocytopenia), hepatotoxicity, renal failure, hyperkalemia.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate toxicity (bone marrow suppression, renal, GI toxicity).
* **Phenytoin:** Increased phenytoin levels.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Diuretics (especially thiazides):** Increased risk of thrombocytopenia in elderly patients.
## Monitoring
* Renal function (serum creatinine, CrCl).
* Complete blood counts (CBC) with differential, especially in patients with G6PD deficiency, prolonged therapy, or those receiving high doses.
* Electrolytes (especially potassium).
* Liver function tests.
* Signs of hypersensitivity reactions.
## Clinical Pearls
* Drink plenty of fluids to prevent crystalluria.
* Use with caution in patients with G6PD deficiency.
* Elderly patients are at increased risk for adverse effects, particularly rash, GI disturbances, and bone marrow suppression.
* Can interfere with urine glucose and bilirubin tests.
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*This information is intended as a quick reference and does not replace comprehensive drug information resources. Always verify current prescribing information and consult relevant guidelines before making clinical decisions.*
