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# Septran (co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic containing trimethoprim and sulfamethoxazole. It inhibits sequential steps in the folic acid synthesis pathway, leading to bacterial cell death.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Shigellosis
* Acute exacerbations of chronic bronchitis
* Certain strains of *Staphylococcus aureus*
## Adult Dosing
Dosing is typically based on the trimethoprim component. Usual adult dose for UTIs and acute exacerbations of chronic bronchitis: 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours. For PCP treatment, doses are higher.
## Pediatric Dosing
Dosing is calculated based on trimethoprim weight-based recommendations, typically 5-10 mg/kg/day divided into two doses. Maximum daily dose should not exceed the adult dose.
## Dose Adjustments
* **Renal Impairment:** Dose adjustment is necessary based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer usual dose every 12-18 hours.
* CrCl < 15 mL/min: Administer usual dose every 24 hours or withhold.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency.
* Documentation of severe adverse reaction (e.g., Stevens-Johnson syndrome) to sulfonamides or related drugs.
## Adverse Effects
Common: Rash, nausea, vomiting, diarrhea.
Serious: Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hyperkalemia, bone marrow suppression (anemia, leukopenia, thrombocytopenia), renal dysfunction, hepatic dysfunction, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels, risk of toxicity.
* **Cyclosporine:** Increased cyclosporine levels, risk of nephrotoxicity.
* **Digoxin:** Increased digoxin levels, risk of toxicity.
## Monitoring
* Renal function (creatinine).
* Complete blood count (CBC) with differential, especially during prolonged therapy.
* Electrolytes, particularly potassium.
* Liver function tests (LFTs) if indicated.
* For patients on warfarin, monitor INR closely.
## Clinical Pearls
* Adequate fluid intake is crucial to prevent crystalluria.
* Advise patients to report any rash, sore throat, or fever promptly.
* Photosensitivity can occur; recommend sun protection.
* Consider folate supplementation for patients on long-term therapy, especially those with risk factors for deficiency.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and local guidelines for complete details and to ensure patient safety.*
