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## Septran (Co-trimoxazole)
### Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis.
### Primary Indications
* **Urinary Tract Infections (UTIs):** Acute uncomplicated UTIs.
* **Pneumocystis jirovecii pneumonia (PCP):** Treatment and prophylaxis.
* **Shigellosis:** Treatment of susceptible strains.
* **Acute exacerbations of chronic bronchitis:** In selected patients.
* **Traveler's diarrhea:** Treatment of susceptible strains.
### Adult Dosing
* **UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3 days.
* **PCP Treatment:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 6 hours for 14-21 days. Higher doses may be used in severe cases.
* **PCP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) daily, or 1 DS tablet three times a week.
* **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 for 5 days.
* **Acute exacerbations of chronic bronchitis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 7 days.
Dosing may be adjusted based on the severity of infection and patient response.
### Pediatric Dosing
Pediatric dosing is generally based on trimethoprim weight-based recommendations.
* **UTIs:** 8 mg/kg/day trimethoprim and 40 mg/kg/day sulfamethoxazole, divided into two doses every 12 hours for 3 days.
* **PCP Treatment:** 15 mg/kg/day trimethoprim and 75 mg/kg/day sulfamethoxazole, divided into four doses every 6 hours for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim and 25 mg/kg/day sulfamethoxazole, divided into two doses daily, or 150 mg/m²/day trimethoprim and 750 mg/m²/day sulfamethoxazole divided into two doses three times a week.
**Note:** For pediatric use, it is important to use formulations appropriate for children, and doses should not exceed the maximum adult dose.
### Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: Usual dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Contraindicated.
### Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Megaloblastic anemia due to folate deficiency.
* Infants < 2 months old (due to risk of kernicterus).
* Severe renal or hepatic impairment.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
### Adverse Effects
* **Hematologic:** Anemia, leukopenia, thrombocytopenia, aplastic anemia, agranulocytosis.
* **Dermatologic:** Rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis), urticaria, photosensitivity.
* **Gastrointestinal:** Nausea, vomiting, diarrhea, abdominal pain, stomatitis.
* **Hepatic:** Elevated liver enzymes, cholestatic jaundice.
* **Renal:** Crystalluria, interstitial nephritis.
* **Other:** Hyperkalemia, headache, dizziness.
### Key Drug Interactions
* **Warfarin:** Increased INR; monitor INR closely.
* **Methotrexate:** Increased risk of bone marrow suppression; monitor CBC.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Increased risk of hyperkalemia.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels and nephrotoxicity.
* **Potent CYP2C9 inhibitors (e.g., fluconazole):** May increase sulfamethoxazole levels.
* **Oral hypoglycemics:** Increased risk of hypoglycemia.
### Monitoring
* Complete blood count (CBC) with differential and platelet count, especially with prolonged therapy or in patients with G6PD deficiency.
* Renal function (BUN, creatinine).
* Liver function tests.
* Electrolytes, particularly potassium.
* INR if the patient is on warfarin.
### Clinical Pearls
* Ensure adequate hydration to prevent crystalluria.
* Co-trimoxazole is teratogenic, especially in the first trimester; avoid use unless benefits outweigh risks.
* Use with caution in patients with G6PD deficiency due to the risk of hemolytic anemia.
* Monitor for signs and symptoms of hypersensitivity reactions.
* The DS tablet contains 160 mg of trimethoprim and 800 mg of sulfamethoxazole.
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*Disclaimer: This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult with a qualified healthcare provider to ensure the information is accurate and appropriate for your specific situation. It is crucial to refer to the most current prescribing information and institutional protocols.*
