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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole, which act synergistically to inhibit folic acid synthesis in bacteria.
## Primary Indications
* **Urinary Tract Infections (UTIs):** Uncomplicated UTIs.
* **Pneumocystis Jirovecii Pneumonia (PCP):** Treatment and prophylaxis.
* **Bacterial Infections:** Including some respiratory, ear, and gastrointestinal infections.
## Adult Dosing
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (800 mg sulfamethoxazole / 160 mg trimethoprim) every 12 hours for 3-7 days.
* **PCP Treatment:** 15 mg/kg/day of trimethoprim component, divided every 6 hours for 14-21 days. (e.g., 2 DS tablets every 6 hours).
* **PCP Prophylaxis:** 1 DS tablet daily or 1 DS tablet three times weekly.
* **Other Infections:** Dosing varies based on severity and pathogen. Typically 1 DS tablet every 12 hours. Maximum recommended dose is usually 4 DS tablets per day.
## Pediatric Dosing
* Dosing is based on the trimethoprim component, typically 8-10 mg/kg/day divided every 12 hours. For example, for a UTI: 8 mg/kg/day of trimethoprim component, divided every 12 hours.
* For PCP treatment in children: 15 mg/kg/day of trimethoprim component, divided every 6 hours.
* For PCP prophylaxis in immunocompromised children: 150 mg/m²/day of trimethoprim component, divided every 12 hours.
* Actual tablet strength should be considered for accurate dosing.
## Dose Adjustments
* **Renal Impairment:** Dose adjustment is necessary. Consult prescribing information for specific recommendations based on creatinine clearance.
* **Hepatic Impairment:** Use with caution.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* History of drug-induced immune thrombocytopenia with either agent.
* Marked liver or renal impairment.
* Megaloblastic anemia due to folate deficiency.
* Prematurity and infants < 2 months (due to risk of kernicterus).
## Adverse Effects
* **Common:** Nausea, vomiting, rash, diarrhea.
* **Serious:** Severe skin reactions (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis), blood dyscrasias (e.g., thrombocytopenia, leukopenia, megaloblastic anemia), hyperkalemia, photosensitivity, crystalluria.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased methotrexate levels.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels, especially in transplant recipients.
* **Phenytoin:** May increase phenytoin levels.
## Monitoring
* Renal and hepatic function.
* Complete blood counts (CBC), especially with prolonged therapy or in patients with G6PD deficiency.
* Electrolytes, particularly potassium.
* Signs of hypersensitivity reactions and skin changes.
* Urine output and pH to prevent crystalluria.
## Clinical Pearls
* Administer with plenty of fluids to reduce the risk of crystalluria.
* Photosensitivity is common; advise patients to use sun protection.
* Discontinue at the first sign of rash.
* Consider a folic acid supplement (5-10 mg daily) in patients on long-term therapy to prevent hematologic complications, unless treating PCP.
**Disclaimer:** Always consult the most current prescribing information and relevant clinical guidelines for complete and up-to-date information.
