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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic containing trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folate synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* *Shigella* infections
* *Haemophilus influenzae* otitis media (certain strains)
## Adult Dosing
* **UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) PO every 12 hours for 3-7 days (uncomplicated) or 7-14 days (complicated).
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 4 doses (PO or IV) for 14-21 days.
* **PCP Prophylaxis:** 1 DS tablet PO daily or 1 DS tablet PO three times weekly.
* **Shigella:** 1 DS tablet PO every 12 hours for 5 days.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **General Infections:** 8-10 mg/kg/day trimethoprim component, divided into 2 doses (PO or IV).
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 4 doses (PO or IV) for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim component, divided into 2 doses (PO).
* **Maximum pediatric dose:** Do not exceed adult doses.
## Dose Adjustments
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 50%.
* **Renal Impairment (CrCl 30-50 mL/min):** Reduce dose by 25%.
* **Hepatic Impairment:** Use with caution; no specific dose adjustment guidelines.
## Contraindications
* Hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency when achievable levels cannot be monitored.
* History of drug-induced thrombocytopenia with either component.
## Adverse Effects
Common: Nausea, vomiting, rash, diarrhea, increased potassium.
Serious: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe rash (DRESS), hepatotoxicity, bone marrow suppression (anemia, leukopenia, thrombocytopenia), hyperkalemia, crystalluria, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels.
* **Oral Hypoglycemics:** May potentiate hypoglycemic effect.
* **Digoxin:** May increase digoxin levels.
## Monitoring
* Renal function (BUN, creatinine)
* Electrolytes (especially potassium)
* Complete blood count (CBC) with differential, particularly during prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs)
* Signs of rash and hypersensitivity reactions.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Monitor for signs of hypersensitivity, especially during the first few weeks of therapy. Discontinue at the first sign of rash.
* Sulfonamides can displace bilirubin from albumin; caution in neonates and patients with hyperbilirubinemia.
* Can interfere with urine glucose and protein testing.
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**Disclaimer:** This information is intended for clinical use and does not replace comprehensive drug information resources. Always consult the most current prescribing information and institutional guidelines before making clinical decisions.
