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# Septran (Co-Trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole. It is a broad-spectrum agent effective against many Gram-positive and Gram-negative bacteria.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Shigellosis
* Acute otitis media (AOM)
* Acute exacerbations of chronic bronchitis (AECB)
* Traveler's diarrhea
## Adult Dosing
Dosing is typically expressed as the amount of **400 mg sulfamethoxazole / 80 mg trimethoprim** component.
* **Uncomplicated UTIs:** 1 DS (double strength) tablet every 12 hours for 3 days.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component, divided into 3-4 doses, for 14-21 days. This is often administered as 2 DS tablets every 6 hours.
* **PJP Prophylaxis:** 1 DS tablet daily, or 1 DS tablet 3 times per week.
* **Shigellosis:** 1 DS tablet every 12 hours for 5 days.
* **AECB:** 1 DS tablet every 12 hours for 7-14 days.
* **Traveler's diarrhea:** 1 DS tablet every 12 hours for 5 days.
Maximum dose for adults generally does not exceed 12 DS tablets per day.
## Pediatric Dosing
Dosing is based on the trimethoprim component (80 mg per DS tablet).
* **General Infections:** 8 mg/kg/day of trimethoprim component, divided into two doses (given every 12 hours). This is typically 1 DS tablet per 50 lbs (22.7 kg) body weight per day, divided into two doses.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component, divided into 3-4 doses for 14-21 days.
* **PJP Prophylaxis:** 5 mg/kg/day of trimethoprim component, divided into two doses, given daily or on alternate days.
## 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 or sulfonamides.
* History of drug-induced thrombocytopenia with either agent.
* Megaloblastic anemia due to folate deficiency.
* Marked liver parenchymal damage.
* Anuria.
* Infants < 2 months of age (increased risk of kernicterus).
## Adverse Effects
* **Common:** Rash (especially in HIV-positive patients), nausea, vomiting, diarrhea.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe skin reactions, hyperkalemia, bone marrow suppression (anemia, leukopenia, thrombocytopenia), hepatotoxicity, renal dysfunction, crystalluria (ensure adequate fluid intake).
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose as needed.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Sulfonylureas:** Increased risk of hypoglycemia.
* **Cyclosporine:** Increased cyclosporine levels.
## Monitoring
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium).
* Complete blood counts (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Signs and symptoms of hypersensitivity reactions and rash.
* Liver function tests.
## Clinical Pearls
* Ensure adequate fluid intake to prevent crystalluria, especially in patients with impaired renal function.
* Sulfonamides can displace bilirubin from albumin, posing a risk of kernicterus in neonates.
* Advise patients to report any rash, sore throat, fever, or mouth sores immediately.
* Co-trimoxazole can interfere with urine glucose testing methods.
**Disclaimer:** This information is a summary and not a substitute for comprehensive prescribing information. Always consult the current official prescribing information and your institution's protocols before making any clinical decisions.
