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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a fixed-dose combination of trimethoprim and sulfamethoxazole, a sulfonamide antibiotic. It is a bacteriostatic agent that inhibits folic acid synthesis in susceptible microorganisms.
## Primary Indications
* Urinary tract infections (UTIs), including acute uncomplicated cystitis and prophylaxis.
* Pneumocystis jirovecii pneumonia (PJP) treatment and prophylaxis.
* Shigellosis.
* Acute otitis media.
* Acute exacerbations of chronic bronchitis.
* Gastroenteritis caused by susceptible organisms.
* Treatment of *Stenotrophomonas maltophilia* infections.
## Adult Dosing
Dosing is based on the trimethoprim component. Standard dose: 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours.
* **UTIs, acute otitis media, acute exacerbations of chronic bronchitis:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 3 days (UTI) or 7-10 days (otitis media, bronchitis).
* **Shigellosis:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 5 days.
* **PJP treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses (e.g., 160 mg/800 mg every 6-8 hours) for 14-21 days.
* **PJP prophylaxis:** 160 mg trimethoprim / 800 mg sulfamethoxazole once daily.
## Pediatric Dosing
Dosing is based on the trimethoprim component. Weight-based dosing is preferred.
* **General infections (e.g., UTIs, otitis media):** 8 mg/kg/day trimethoprim component divided into two doses every 12 hours. For children over 12 years, standard adult dosing can be used.
* **PJP treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses (e.g., 160 mg/800 mg every 6-8 hours) for 14-21 days.
* **PJP prophylaxis:** 5 mg/kg/day trimethoprim component divided into two doses every 12 hours, given on 3 consecutive days per week. Maximum daily dose is 320 mg trimethoprim component.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: Standard dose.
* CrCl 15-30 mL/min: Half the standard dose.
* CrCl < 15 mL/min: Avoid use or administer one-quarter the standard dose every 12 hours.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Infants less than 2 months of age (risk of kernicterus).
* History of drug-induced immune thrombocytopenia with either component.
* Severe renal insufficiency where frequent laboratory monitoring is impossible.
* Severe hepatic insufficiency.
* Megaloblastic anemia due to folate deficiency.
## Adverse Effects
* **Common:** Rash (including Stevens-Johnson syndrome, toxic epidermal necrolysis), nausea, vomiting, diarrhea, anorexia.
* **Hematologic:** Leukopenia, thrombocytopenia, neutropenia, megaloblastic anemia, aplastic anemia, eosinophilia.
* **Hepatic:** Elevated liver enzymes, cholestatic jaundice, hepatitis.
* **Renal:** Interstitial nephritis, elevated creatinine.
* **Other:** Hyperkalemia, hyponatremia, hypoglycemia, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and potential for bone marrow suppression.
* **Diuretics (especially thiazides in elderly):** Increased risk of thrombocytopenia.
* **Cyclosporine:** Increased cyclosporine levels.
* **Potassium:** May reduce the efficacy of potassium supplements.
* **Rifampin:** May increase the metabolism of sulfamethoxazole.
## Monitoring
* **Renal Function:** Monitor serum creatinine and BUN, especially in patients with renal impairment.
* **Complete Blood Count (CBC):** Monitor for hematologic abnormalities, particularly with prolonged therapy or in immunocompromised patients. Consider monitoring weekly.
* **Electrolytes:** Monitor potassium and sodium levels.
* **Liver Function Tests:** Monitor if hepatic dysfunction is suspected.
* **Therapeutic Drug Monitoring (TDM):** Not routinely required, but may be considered for critically ill patients or those with suspected suboptimal levels.
## Clinical Pearls
* Administer oral co-trimoxazole with a full glass of water and encourage adequate fluid intake to prevent crystalluria.
* Take with food or milk to minimize gastrointestinal upset.
* Discontinue immediately if rash develops.
* Sulfonamides can displace bilirubin from albumin; use with caution in neonates and in patients with severe liver disease.
* Use cautiously in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency due to the risk of hemolytic anemia.
* Concurrent administration of leucovorin may be required for patients receiving high-dose co-trimoxazole for PJP treatment to prevent bone marrow suppression.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making therapeutic decisions.*
