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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination of trimethoprim and sulfamethoxazole, a synergistic antibacterial agent.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Certain types of bacterial pneumonia, shigellosis, and traveler's diarrhea.
## Adult Dosing
* **Uncomplicated UTIs:** 1 DS (double strength) tablet every 12 hours for 3-5 days.
* **PJP Treatment:** 15 mg/kg/day trimethoprim component, given as 75 mg/kg/day sulfamethoxazole component, in 3-4 divided doses for 14-21 days. Maximum daily dose of 8 DS tablets.
* **PJP Prophylaxis:** 1 DS tablet once daily, or 1 DS tablet three times a week.
* **Other infections:** Dosing varies by indication. A common regimen is 1-2 DS tablets every 12 hours. Maximum daily dose of 8 DS tablets.
## Pediatric Dosing
* Dosing is based on the trimethoprim component, 5 mg/kg/dose every 12 hours, and the sulfamethoxazole component, 25 mg/kg/dose every 12 hours.
* **PJP Treatment:** 15 mg/kg/day trimethoprim component, given as 75 mg/kg/day sulfamethoxazole component, in 3-4 divided doses for 14-21 days. Maximum daily dose of 8 DS tablets.
* **PJP Prophylaxis:** 5 mg/kg/dose trimethoprim component, given as 25 mg/kg/dose sulfamethoxazole component, once daily, or 10 mg/kg/dose trimethoprim component with 50 mg/kg/dose sulfamethoxazole component every 12 hours, 3 times a week.
* Dosing for UTIs and other infections in children varies and is often calculated based on weight and severity.
## Dose Adjustments
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 25-50%.
* **Hepatic Impairment:** Use with caution; monitor liver function.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (due to risk of kernicterus).
* Severe renal or hepatic insufficiency when pharmacokinetic monitoring is unavailable.
* History of drug-induced thrombocytopenia with either component.
## Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea.
* **Serious:** Severe dermatologic reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), blood dyscrasias (anemia, thrombocytopenia, leukopenia, agranulocytosis), hyperkalemia, hepatic injury, renal injury, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased methotrexate toxicity.
* **Potassium-sparing diuretics (e.g., spironolactone, ACE inhibitors):** Increased risk of hyperkalemia.
* **Potassium supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels.
## Monitoring
* Complete blood count (CBC) with differential and platelet count, especially with prolonged use or in immunocompromised patients.
* Renal and hepatic function tests.
* Electrolytes, particularly potassium.
* Skin for rash and signs of hypersensitivity.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Caution in patients with G6PD deficiency due to risk of hemolytic anemia.
* Sulfonamides can displace bilirubin from albumin; avoid in late pregnancy and in newborns.
* If a patient develops a rash, discontinue immediately and assess for hypersensitivity.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before making clinical decisions.*
