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# Septran (Co-Trimoxazole)
## Overview
Septran is a combination antibiotic containing sulfamethoxazole and trimethoprim. 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
* Traveler's diarrhea
* Shigellosis
* Acute exacerbations of chronic bronchitis
* Otitis media
## Adult Dosing
* **General Infections:** Typically 160 mg trimethoprim/800 mg sulfamethoxazole (one double-strength tablet) every 12 hours.
* **UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 3 days.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim and 75-100 mg/kg/day sulfamethoxazole, divided into 3-4 doses, for 14-21 days.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole once daily, or 80 mg trimethoprim/400 mg sulfamethoxazole twice daily, or 160 mg trimethoprim/800 mg sulfamethoxazole three times weekly.
* **Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for up to 5 days.
* **Maximum Dose:** Generally, do not exceed 640 mg trimethoprim or 3200 mg sulfamethoxazole per day, except for severe infections like PJP treatment.
## Pediatric Dosing
Dosing is based on trimethoprim component, typically 8-10 mg/kg/day, divided every 12 hours. Sulfamethoxazole dose is 40-50 mg/kg/day, divided every 12 hours.
* **General Infections:** 8-10 mg/kg/day trimethoprim and 40-50 mg/kg/day sulfamethoxazole, divided every 12 hours.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim and 25 mg/kg/day sulfamethoxazole, divided into two doses daily.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim and 75-100 mg/kg/day sulfamethoxazole, divided into 3-4 doses for 14-21 days.
* **Note:** Use with caution in neonates due to risk of kernicterus. Generally not recommended in infants < 2 months of age.
## Dose Adjustments
* **Renal Impairment:** Adjust dose based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Give usual dose every 18 hours.
* CrCl < 15 mL/min: Avoid use or give half the usual dose every 24 hours.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation.
* Documented megaloblastic anemia due to folate deficiency.
* Premature infants and term infants in the first 2 months of life.
* Patients with severe renal insufficiency (CrCl < 15 mL/min) if plasma levels cannot be monitored.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
## Adverse Effects
Common: Rash, nausea, vomiting, diarrhea, hyperkalemia, elevated liver enzymes.
Serious: Severe cutaneous reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), aplastic anemia, agranulocytosis, thrombocytopenia, hyponatremia, hyperkalemia, renal failure, interstitial nephritis, photosensitivity, C. difficile-associated diarrhea.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics/Potassium Supplements:** Increased risk of hyperkalemia. Monitor potassium levels.
* **Methotrexate:** Increased methotrexate levels and toxicity. Consider folate supplementation or avoiding concomitant use.
* **Digoxin:** Increased digoxin levels. Monitor digoxin levels.
* **Potassium-Chloride Supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels and nephrotoxicity.
* **Phenytoin:** Increased phenytoin levels. Monitor phenytoin levels.
* **Rosuvastatin:** Increased rosuvastatin levels.
* **Sulfonylureas:** Increased risk of hypoglycemia.
## Monitoring
* Complete blood counts (CBC) with differential before and during treatment, especially in prolonged therapy or patients with G6PD deficiency.
* Renal function (BUN, creatinine).
* Liver function tests.
* Electrolytes (especially potassium).
* Therapeutic drug levels may be considered in specific situations (e.g., severe infection, renal impairment).
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Photosensitivity can occur; recommend sun protection.
* Rash is a common side effect; discontinue if severe.
* Folic acid supplementation (e.g., 5 mg daily) is recommended for patients receiving long-term therapy, particularly those at risk of folate deficiency (e.g., elderly, pregnant women, malnourished patients).
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*Always consult the most current prescribing information and local institutional guidelines for definitive drug management decisions.*
