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## Septran (Co-trimoxazole)
### Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole.
### Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Shigellosis
* *Haemophilus influenzae* otitis media
### Adult Dosing
* **UTI:** 160 mg trimethoprim / 800 mg sulfamethoxazole (TMP/SMX) every 12 hours for 3-7 days.
* **PJP Treatment:** 15-20 mg/kg/day TMP component divided into 3-4 doses, given with 5 mg/kg/day sulfadiazine (or equivalent SMX dose) for 14-21 days.
* **PJP Prophylaxis:** 160 mg TMP / 800 mg SMX daily or 160 mg TMP / 800 mg SMX three times weekly.
### Pediatric Dosing
Dosing is based on the trimethoprim component.
* **UTI:** 8-10 mg/kg/day TMP component divided into two doses.
* **PJP Treatment:** 15-20 mg/kg/day TMP component divided into 3-4 doses.
* **PJP Prophylaxis:** 5-7.5 mg/kg/day TMP component divided into two doses.
### Dose Adjustments
* **Renal Impairment (CrCl):**
* CrCl > 30 mL/min: No adjustment.
* CrCl 15-30 mL/min: Administer 75% of the standard dose.
* CrCl < 15 mL/min: Avoid use.
### Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age.
* Severe renal or hepatic insufficiency where urine and blood levels cannot be monitored.
### Adverse Effects
Common adverse effects include rash, pruritus, nausea, vomiting, and diarrhea. Serious adverse effects include Stevens-Johnson syndrome, toxic epidermal necrolysis, severe hematologic reactions (anemia, thrombocytopenia, neutropenia), hyperkalemia, and crystalluria.
### 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, potentially leading to toxicity.
* **Rifampin:** May decrease co-trimoxazole levels and vice-versa.
### Monitoring
* Renal function (BUN, creatinine).
* Complete blood count (CBC) with differential, especially in prolonged therapy or immunocompromised patients.
* Electrolytes, particularly potassium.
* Signs of hypersensitivity reactions.
* For patients on warfarin, monitor INR.
### Clinical Pearls
* Ensure adequate fluid intake to prevent crystalluria.
* Advise patients to report any rash, sore throat, or fever immediately.
* Discontinue if signs of hypersensitivity or hematologic toxicity occur.
* Sulfonamide-induced photosensitivity can occur; advise sun protection.
**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines for definitive patient management.
