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## Septran (Co-trimoxazole)
### Overview
Septran is a combination antibiotic containing trimethoprim and sulfamethoxazole in a 1:5 ratio.
### Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea
### Adult Dosing
* **General UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component, divided every 6 hours, for 14-21 days.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) daily or 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) three times weekly.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 5 days.
* **Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours. Duration typically 3-5 days.
### Pediatric Dosing
* Dosing is based on the trimethoprim component, 5-10 mg/kg/day, divided every 12 hours.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component, divided every 6 hours.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim component, divided once daily.
* Actual dosage depends on indication and weight. Use available pediatric formulations or calculate based on tablet strength.
### Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer 75% of the standard dose.
* CrCl < 15 mL/min: Avoid use; if unavoidable, use 50% of the standard dose and monitor closely.
* **Hepatic Impairment:** Use with caution.
### Contraindications
* Documented hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation.
* Severe renal insufficiency (CrCl < 15 mL/min) if plasma concentrations cannot be monitored.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* G6PD deficiency (risk of hemolytic anemia).
### Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea, eosinophilia, hyperkalemia.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe skin reactions, bone marrow suppression (anemia, leukopenia, thrombocytopenia), hyperkalemia, renal impairment, liver dysfunction, photosensitivity, aseptic meningitis.
### Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors, ARBs, Potassium-sparing diuretics, Potassium supplements:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and toxicity. Avoid coadministration or monitor methotrexate levels.
* **Potassium-rich foods/supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
* **Digoxin:** May increase digoxin levels. Monitor digoxin levels.
### Monitoring
* **Renal function:** Baseline and periodically, especially in patients with renal impairment.
* **Complete blood count (CBC):** Baseline and periodically, especially in patients on long-term therapy or with risk factors for hematologic toxicity.
* **Electrolytes:** Particularly potassium, especially in patients with renal impairment or taking other medications that affect potassium.
* **Liver function tests:** Periodically.
* **Signs of hypersensitivity:** Monitor for rash and other signs of allergic reaction.
### Clinical Pearls
* Co-trimoxazole should be administered with plenty of fluids to prevent crystalluria.
* Sulfonamides can displace bilirubin from albumin; avoid in infants and pregnant women near term.
* Long-term use can lead to folate deficiency. Consider folate supplementation if indicated.
* Discontinue immediately if a rash develops.
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*Disclaimer: This information is intended for clinical use and is not a substitute for professional medical judgment. Always consult the most current prescribing information and institutional protocols.*
