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## Septran (Co-trimoxazole)
### Overview
Septran is a combination antibiotic of trimethoprim and sulfamethoxazole.
### Primary Indications
* **Urinary Tract Infections (UTIs):** Acute uncomplicated cystitis, acute exacerbations of chronic bronchitis, and prophylaxis.
* **Pneumocystis jirovecii pneumonia (PCP):** Treatment and prophylaxis.
* **Traveler's Diarrhea:** Treatment.
* **Shigellosis:** Treatment.
* **Otitis Media:** Treatment.
### Adult Dosing
* **UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days for uncomplicated cystitis. Longer durations may be needed for other indications.
* **PCP Prophylaxis:** 1 DS tablet daily.
* **PCP Treatment:** 15 mg/kg/day trimethoprim component (divided into 3-4 doses) with 75 mg/kg/day sulfamethoxazole component, typically for 14-21 days. This usually translates to 2 DS tablets every 6 hours.
* **Traveler's Diarrhea:** 1 DS tablet every 12 hours for 5 days.
### Pediatric Dosing
Dosing is based on the trimethoprim component.
* **General Infections:** 8 mg/kg/day trimethoprim component, divided every 12 hours.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim component (given as 2 divided doses) or 150 mg/m²/day sulfamethoxazole component.
* **PCP Treatment:** 15 mg/kg/day trimethoprim component, divided every 6 hours.
*Note: Specific dosages for pediatric patients are often guided by local protocols and should be confirmed.*
### Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use.
### Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency where urine and blood levels cannot be monitored.
* History of drug-induced thrombocytopenia with platelet counts less than 50,000/mm³.
### Adverse Effects
* **Common:** Rash (can be severe, including Stevens-Johnson syndrome/toxic epidermal necrolysis), hyperkalemia, gastrointestinal upset (nausea, vomiting, diarrhea), increased liver enzymes.
* **Serious:** Hematologic abnormalities (anemia, leukopenia, thrombocytopenia, agranulocytosis), severe skin reactions, hyperkalemia, hyponatremia, crystalluria (ensure adequate fluid intake), photosensitivity, hepatic necrosis, pancreatitis.
### Key Drug Interactions
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased risk of methotrexate toxicity due to displacement from plasma protein binding and inhibition of dihydrofolate reductase.
* **Phenytoin:** Increased phenytoin levels.
* **Sulfonylureas (e.g., glyburide, glipizide):** Potentiated hypoglycemic effects.
* **Thiazide Diuretics:** Increased risk of thrombocytopenia, particularly in the elderly.
* **Potassium Supplements:** Increased risk of hyperkalemia.
### Monitoring
* **Renal function (creatinine).**
* **Complete blood counts (CBC) with differential** during prolonged therapy, especially in elderly patients or those with G6PD deficiency.
* **Electrolytes (especially potassium)**, particularly in patients with renal impairment or those taking other agents that affect potassium.
* **Liver function tests** with prolonged therapy.
* **Fluid intake and urine output** to prevent crystalluria.
### Clinical Pearls
* Co-trimoxazole can cause a false-positive for urinary protein when tested with sulfosalicylic acid.
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Photosensitivity reactions can occur; advise patients to use sun protection.
* Discontinue if rash develops, unless it is clearly not drug-related.
* Monitor potassium closely, especially in patients with renal dysfunction or those on ACE inhibitors/ARBs.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and local institutional guidelines before making clinical decisions.*
