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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis. It is available in oral and intravenous formulations.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea (enterotoxigenic E. coli)
* Nocardiosis
## Adult Dosing
* **Urinary Tract Infections:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3-7 days.
* **Pneumocystis jirovecii pneumonia (PJP) Treatment:** 15-20 mg/kg/day trimethoprim component, given in 3-4 divided doses every 12-24 hours for 14-21 days.
* **PJP Prophylaxis:** 1 double-strength tablet daily, or 1 single-strength tablet daily, or 1 double-strength tablet 3 times weekly.
* **Other Indications:** Dosing varies; typically 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours. Consult specific guidelines.
## Pediatric Dosing
Dosing is based on the trimethoprim component: 8-10 mg/kg/day divided into two doses every 12 hours for UTIs and most other infections. For PJP treatment, 15-20 mg/kg/day divided into two doses every 12 hours.
* **Maximum pediatric dose:** Should not exceed the adult dose.
* **Note:** Specific dosing for children younger than 2 months is generally not recommended due to risk of kernicterus.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: Full dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use or give 1/4 the usual dose.
* **Hepatic Impairment:** Use with caution.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation.
* History of drug-induced immune thrombocytopenia with either agent.
* Megaloblastic anemia due to folate deficiency.
* Severe renal insufficiency where urine output cannot be monitored.
* Infants less than 2 months of age.
* Pregnancy at term and breastfeeding of newborn infants.
## Adverse Effects
* **Common:** Nausea, vomiting, rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis, which can be life-threatening), hyperkalemia, photosensitivity.
* **Less Common:** Diarrhea, leukopenia, thrombocytopenia, eosinophilia, elevated liver enzymes, dizziness, headache.
## Key Drug Interactions
* **ACE inhibitors & ARBs:** Increased risk of hyperkalemia.
* **Diuretics (especially thiazides):** Increased risk of hyperkalemia, particularly in elderly patients.
* **Warfarin:** Increased INR; monitor INR closely and adjust warfarin dose as needed.
* **Methotrexate:** Increased risk of methotrexate toxicity; monitor for hematologic toxicity.
* **Potassium supplements and potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels, potentially leading to nephrotoxicity.
## Monitoring
* **Renal function** (serum creatinine, CrCl)
* **Electrolytes** (especially potassium)
* **Complete blood counts (CBC)** with differential, particularly with prolonged therapy or in patients with G6PD deficiency.
* **Liver function tests (LFTs)**
* **Signs of hypersensitivity reactions**
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Sulfonamides can cause a false-positive test for urinary glucose with certain urine testing methods.
* Co-trimoxazole can potentiate the effects of oral hypoglycemic agents.
* Avoid concurrent use with folic acid supplements unless the patient has a confirmed folate deficiency and is being treated for it.
* IV formulation should be infused slowly over 60-90 minutes and not given as a bolus.
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**Disclaimer:** This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and local protocols for complete and up-to-date guidance.
