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# Co-Trimoxazole (Septran)
## Overview
Co-trimoxazole is a combination antibiotic containing trimethoprim and sulfamethoxazole, which work synergistically to inhibit folic acid synthesis in bacteria.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Bacterial respiratory tract infections (e.g., acute exacerbations of chronic bronchitis)
* Shigellosis
* Otitis media
## Adult Dosing
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) orally every 12 hours for 3 days.
* **Complicated UTIs and other infections:** 1 DS tablet orally every 12 hours. Duration varies by indication (e.g., 7-14 days for UTIs, 21 days for PJP treatment).
* **PJP Prophylaxis:** 1 DS tablet orally once daily.
* **Maximum Dose:** Generally not to exceed 4 DS tablets (640 mg trimethoprim/3200 mg sulfamethoxazole) daily for serious infections.
## Pediatric Dosing
Dosing is based on trimethoprim component (9-12 mg/kg/day) divided every 12 hours. Sulfamethoxazole dose will follow proportionally.
* **General Infections:** 9-12 mg/kg/day of trimethoprim, given in 2 divided doses.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim, given in 4 divided doses.
* **PJP Prophylaxis:** 7.5 mg/kg/day of trimethoprim, given in 2 divided doses.
* **Maximum Dose:** Not to exceed the adult maximum 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.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
## Adverse Effects
Common: Rash, nausea, vomiting, diarrhea.
Serious: Stevens-Johnson syndrome, toxic epidermal necrolysis, severe rash (e.g., DRESS), hyperkalemia, bone marrow suppression (anemia, leukopenia, thrombocytopenia), crystalluria, hepatic injury, 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.
* **Cyclosporine:** Increased cyclosporine levels, particularly in transplant patients.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Dapsone:** Increased dapsone levels.
## Monitoring
* **Renal Function:** Baseline and periodically, especially in elderly or those with pre-existing renal disease.
* **Complete Blood Count (CBC):** Baseline and periodically, especially with prolonged therapy or in immunocompromised patients.
* **Electrolytes:** Particularly potassium, especially with concurrent use of ACE inhibitors, ARBs, or potassium supplements.
* **Liver Function Tests:** Periodically, especially in patients with risk factors for hepatic injury.
* **Signs of Rash/Hypersensitivity:** Educate patients to report any skin changes immediately.
## Clinical Pearls
* Ensure adequate fluid intake to prevent crystalluria.
* Monitor potassium closely, especially in at-risk patients.
* Co-trimoxazole is a common cause of drug-induced rash, including severe and life-threatening reactions.
* Dosing for specific indications, especially in pediatrics, should be confirmed with current institutional protocols or guidelines.
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*This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant guidelines before making any clinical decisions.*
