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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 (PCP) prophylaxis and treatment
* *Shigella* enteritis
* *Haemophilus influenzae* otitis media
* Acute exacerbations of chronic bronchitis
## Adult Dosing
Dosing is typically based on the trimethoprim component. Standard dose: 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours.
* **Uncomplicated UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 3 days.
* **Complicated UTIs and other infections:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours. Duration varies by indication.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses, along with 75-100 mg/kg/day sulfamethoxazole component, for 14-21 days.
* **PCP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole daily or every other day.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **General Pediatric Infections:** 8 mg/kg/day trimethoprim component and 40 mg/kg/day sulfamethoxazole component, divided into two doses every 12 hours.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses, along with 75-100 mg/kg/day sulfamethoxazole component, for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim component and 25 mg/kg/day sulfamethoxazole component, divided into two doses daily for 3 days a week or every other day.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: Standard dose.
* CrCl 15-30 mL/min: Half of the standard dose.
* CrCl < 15 mL/min: Avoid use or use with extreme caution at one-quarter of the standard dose.
## Contraindications
* Hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic impairment.
* History of drug-induced immune thrombocytopenia with either component.
* Megaloblastic anemia due to folate deficiency.
## Adverse Effects
Common: Rash, nausea, vomiting, diarrhea, pruritus.
Serious: Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis, hyperkalemia, bone marrow suppression (including aplastic anemia, thrombocytopenia, leukopenia), crystalluria, hepatic necrosis, C. difficile-associated diarrhea.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels, risk of bone marrow suppression.
* **Digoxin:** Increased digoxin levels.
* **Sulfonylureas:** Enhanced hypoglycemic effect.
* **Potassium Supplements/Supplements containing Potassium:** Increased risk of hyperkalemia.
## Monitoring
* Renal function (BUN, 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.
* Monitor for diarrhea, especially *C. difficile*-associated diarrhea.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Administer with food to minimize gastrointestinal upset.
* Discontinue immediately if rash develops, as it may be a sign of severe hypersensitivity.
* Use with caution in patients with G6PD deficiency due to risk of hemolytic anemia.
This information is a summary and does not replace current prescribing information or professional judgment. Always consult the most up-to-date product monograph and clinical guidelines.
