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# Septra (Trimethoprim/Sulfamethoxazole)
## Overview
Septra is a combination antibiotic containing trimethoprim and sulfamethoxazole in a 1:5 ratio. It is bactericidal and inhibits folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Acute exacerbations of chronic bronchitis
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Shigellosis
* Traveler's diarrhea (due to susceptible organisms)
## Adult Dosing
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim / 800 mg sulfamethoxazole) orally every 12 hours for 3 days.
* **PCP Treatment:** 15 mg/kg/day trimethoprim component, divided into 3-4 doses, orally or IV for 14-21 days.
* **PCP Prophylaxis:** 1 DS tablet orally every day, or 1 DS tablet orally 3 times a week.
* **Other Indications:** Dosing varies by indication. A common regimen for other infections is 1 DS tablet orally every 12 hours.
## Pediatric Dosing
* Dosing is based on the trimethoprim component, typically 8-10 mg/kg/day divided into 2 doses.
* **Uncomplicated UTIs:** 8 mg/kg/day of trimethoprim, divided into 2 doses, for 3 days.
* **PCP Treatment:** 15 mg/kg/day of trimethoprim, divided into 3-4 doses, for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day of trimethoprim, divided into 2 doses, daily or 3 times a week.
* *Note: Actual tablet strength and formulation should be confirmed. Dosing for children < 2 months is generally not recommended due to risk of kernicterus.*
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Half the standard dose.
* CrCl < 15 mL/min: Avoid use.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age.
* Severe renal or hepatic impairment.
* Porphyria.
## Adverse Effects
* **Common:** Nausea, vomiting, rash (can be severe, including Stevens-Johnson syndrome and toxic epidermal necrolysis), urticaria, hyperkalemia, elevated liver enzymes.
* **Less Common:** Diarrhea, headache, dizziness, leukopenia, thrombocytopenia, eosinophilia, crystalluria (ensure adequate fluid intake).
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate toxicity (bone marrow suppression).
* **Diuretics (Thiazide, Loop):** Increased risk of thrombocytopenia, especially in elderly patients.
* **Tricyclic Antidepressants:** Potential for reduced efficacy of TCAs.
* **Potassium Supplements:** Increased risk of hyperkalemia.
## Monitoring
* Renal function (serum creatinine).
* Electrolytes (especially potassium).
* Complete blood count (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests.
* Signs of hypersensitivity reactions.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Monitor for rash closely, as it can indicate a serious hypersensitivity reaction.
* Trimethoprim component can cause a reversible increase in serum creatinine without affecting glomerular filtration rate.
* Concurrent use with folic acid can decrease the efficacy of trimethoprim/sulfamethoxazole.
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*This information is intended for healthcare professionals. Please consult the current prescribing information for complete details and to verify dosages and indications specific to your institution and patient.*
