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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)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Certain respiratory tract infections
* Certain gastrointestinal infections (e.g., Shigellosis)
### Adult Dosing
* **UTIs (uncomplicated):** 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) PO every 12 hours for 3-7 days.
* **UTIs (complicated):** 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) PO every 12 hours for 7-14 days.
* **PCP Prophylaxis:** 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) PO once daily or 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) PO three times weekly.
* **PCP Treatment:** 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) PO every 6 hours for 14-21 days. Higher doses may be used intravenously.
### Pediatric Dosing
Dosing is based on the trimethoprim component, typically 5-10 mg/kg/day divided into two doses.
* **General Infections:** 8 mg trimethoprim / 40 mg sulfamethoxazole per 5 mL suspension, or 1 DS tablet (160 mg/800 mg) PO every 12 hours. The dose is calculated as 10 mg/kg/day of trimethoprim.
* **PCP Prophylaxis:** 5 mg/kg/day of trimethoprim, given as 1 DS tablet PO three times weekly.
* **PCP Treatment:** 15-20 mg/kg/day of trimethoprim divided every 6 hours.
**Note:** Specific pediatric dosing should be confirmed based on the indication, severity, and local protocols.
### 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 sulfamethoxazole.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
* Megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (due to risk of kernicterus).
* Severe renal or hepatic impairment.
### Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, rash.
* **Serious:**
* Hypersensitivity reactions (including Stevens-Johnson syndrome, toxic epidermal necrolysis).
* Hematologic abnormalities (anemia, leukopenia, thrombocytopenia).
* Hyperkalemia.
* Hepatotoxicity.
* Renal toxicity.
* Photosensitivity.
* Hypoglycemia.
### Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Cyclosporine:** Increased cyclosporine levels.
* **Sulfonylureas:** Increased hypoglycemic effect.
* **Potent CYP2C9 inhibitors:** May increase sulfamethoxazole levels.
### Monitoring
* Renal function (serum creatinine, BUN).
* Electrolytes, especially potassium.
* Complete blood counts (CBC) with differential, particularly during prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs).
* Signs of hypersensitivity reactions.
### Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Rash should be reported immediately to a healthcare provider, as it can be a sign of severe hypersensitivity.
* Co-trimoxazole is a common cause of drug-induced fever.
* For PCP treatment, adequate hydration is crucial to prevent renal toxicity.
**Disclaimer:** This information is for educational purposes only and does not substitute for professional medical advice. Always verify current prescribing information and guidelines with the most recent drug monographs, institutional protocols, or a qualified healthcare provider before making any clinical decisions.
