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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic, consisting of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Certain types of bacterial gastroenteritis
* Acute otitis media
* Acute exacerbations of chronic bronchitis
## Adult Dosing
Dosing is typically expressed as a total daily dose of trimethoprim/sulfamethoxazole. Standard strength tablets contain 80 mg trimethoprim and 400 mg sulfamethoxazole. Double strength tablets contain 160 mg trimethoprim and 800 mg sulfamethoxazole.
* **Uncomplicated UTIs:** 1 double strength tablet every 12 hours for 3-7 days.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component, divided into 3-4 doses, for 14-21 days. (e.g., 2 double strength tablets every 8 hours). Maximum daily dose often capped at 1600 mg trimethoprim / 8000 mg sulfamethoxazole.
* **PJP Prophylaxis:** 1 double strength tablet once daily, or 1 double strength tablet three times a week.
Exact dosing for other indications may vary based on local protocols and severity of infection.
## Pediatric Dosing
Dosing is calculated based on the trimethoprim component, usually 10-20 mg/kg/day divided every 12 hours. Sulfamethoxazole dose is given in a 5:1 ratio to trimethoprim.
* **General Infections:** 10 mg/kg/day of trimethoprim component, divided every 12 hours.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component, divided every 8 hours.
* **PJP Prophylaxis:** 10 mg/kg/day of trimethoprim component, divided every 12 hours, or 150 mg/m²/day of trimethoprim component, divided every 12 hours.
Maximum pediatric dose is generally 160 mg trimethoprim / 800 mg sulfamethoxazole per dose.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Reduce dose by 50%.
* CrCl < 15 mL/min: Avoid use or use with extreme caution and close monitoring.
* **Hepatic Impairment:** Use with caution; dose adjustment may be necessary.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or 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 sulfonamides or trimethoprim.
## Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea.
* **Serious:** Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hypersensitivity reactions, hematologic toxicity (anemia, thrombocytopenia, leukopenia, agranulocytosis), hyperkalemia, liver injury, kidney injury.
## Key Drug Interactions
* **Warfarin:** Increased INR; monitor INR closely.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Increased risk of hyperkalemia.
* **Methotrexate:** Increased risk of methotrexate toxicity due to inhibition of dihydrofolate reductase.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Potassium supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels may occur, especially in transplant recipients.
## Monitoring
* **Renal function (creatinine)**
* **Complete blood count (CBC) with differential**, especially with prolonged therapy or in immunocompromised patients.
* **Electrolytes**, particularly potassium.
* **Liver function tests**
* **Signs of hypersensitivity reactions** (rash, fever)
## Clinical Pearls
* Ensure adequate fluid intake to prevent crystalluria.
* Co-trimoxazole is a potent inhibitor of CYP2C8 and 2C9, increasing the risk of toxicity for narrow therapeutic index drugs metabolized by these enzymes (e.g., warfarin, phenytoin).
* Monitor for signs of hyperkalemia, especially in patients with renal impairment or those taking other medications that can increase potassium.
* Consider folate supplementation for patients on long-term co-trimoxazole therapy, especially those with pre-existing folate deficiency or at risk.
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*Disclaimer: This information is for educational purposes and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines for definitive drug management decisions.*
