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# Septran (Co-Trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* *Pneumocystis jirovecii* pneumonia (PCP) prophylaxis and treatment
* Acute otitis media
* Acute exacerbations of chronic bronchitis
* Traveler's diarrhea
## Adult Dosing
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) orally twice daily for 3 days.
* **PCP Treatment:** 15 mg/kg/day trimethoprim component, divided into 4 doses (every 6 hours) orally or IV, for 14-21 days.
* **PCP Prophylaxis:** 1 DS tablet orally once daily, or 1 DS tablet orally 3 times a week.
* **Other Indications:** Dosing varies; typically 1-2 DS tablets orally or IV every 12 hours. Consult specific guidelines for indications like traveler's diarrhea or shigellosis.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **General Infections:** 8-10 mg/kg/day of trimethoprim component, divided into 2 doses orally or IV every 12 hours.
* **PCP Treatment:** 15 mg/kg/day trimethoprim component, divided into 4 doses (every 6 hours) orally or IV, for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim component, divided into 2 doses orally every 12 hours, or 150 mg/m²/day sulfamethoxazole component, divided into 2 doses. Maximum daily dose for prophylaxis is 1 DS tablet daily.
* *Note:* Use in infants younger than 2 months is generally not recommended due to risk of kernicterus.
## Dose Adjustments
* **Renal Impairment (CrCl mL/min):**
* CrCl > 30: No adjustment needed.
* 15-30: Administer 75% of the standard dose.
* < 15: Avoid use or administer 50% of the standard dose at 12-hour intervals.
* **Hepatic Impairment:** Use with caution; no specific dosing adjustments are established.
## Contraindications
* Hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Premature infants and infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency where frequent monitoring is not feasible.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis, particularly in patients with HIV), hyperkalemia, elevated liver enzymes.
Less Common: Bone marrow suppression (anemia, leukopenia, thrombocytopenia), crystalluria (ensure adequate hydration), photosensitivity, interstitial nephritis.
## 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 risk of methotrexate-induced myelosuppression.
* **Dapsone:** Increased risk of dapsone-induced methemoglobinemia and hemolysis.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** May increase cyclosporine levels, especially in transplant patients.
* **Oral Hypoglycemics:** Increased risk of hypoglycemia.
## Monitoring
* Renal function (serum creatinine).
* Complete blood counts (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Electrolytes (especially potassium).
* Liver function tests.
* Fluid intake and urine output to prevent crystalluria.
* INR if patient is on warfarin.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Monitor for rash, especially in the first 2 weeks of therapy, and discontinue immediately if severe.
* Co-trimoxazole can interfere with certain laboratory tests (e.g., creatinine measurement by alkaline picrate method, falsely elevating results).
* Dosing for infections not listed here, or for specific patient populations (e.g., immunocompromised), may differ; consult institutional guidelines or infectious disease specialists.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the official prescribing information and current clinical guidelines for the most accurate and up-to-date recommendations before prescribing or dispensing any medication.
