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# Septra (Trimethoprim-Sulfamethoxazole)
## Overview
Septra is a combination antibiotic containing trimethoprim and sulfamethoxazole in a 1:5 ratio. It is a broad-spectrum bacteriostatic agent that inhibits folic acid synthesis.
## Primary Indications
* Urinary Tract Infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Acute otitis media
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea (enterotoxigenic E. coli)
## Adult Dosing
Dosing is typically based on the trimethoprim component.
* **Uncomplicated UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3 days.
* **PJP Treatment:** 15 mg/kg/day trimethoprim divided into 3-4 doses (given orally or IV) for 14-21 days.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) once daily, or 160 mg trimethoprim/800 mg sulfamethoxazole every other day.
* **Other Infections:** Dosing varies by indication and severity. A common regimen is 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours.
## Pediatric Dosing
Dosing is typically based on the trimethoprim component and the patient's weight.
* **PJP Treatment:** 15 mg/kg/day trimethoprim divided into 3-4 doses (given orally or IV) for 14-21 days.
* **PJP Prophylaxis:** 150 mg/m²/day trimethoprim orally divided into 2 doses, on 3 consecutive days per week. Alternatively, 5 mg/kg/day trimethoprim (maximum 160 mg) orally once daily.
* **Other Infections (e.g., UTIs, otitis media):** Generally 8 mg/kg/day trimethoprim divided into 2 doses. For UTIs, the course is typically 7-14 days; for otitis media, 10 days.
## Dose Adjustments
* **Renal Impairment (CrCl > 30 mL/min):** No adjustment needed.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 50%.
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use.
## Contraindications
* Hypersensitivity to trimethoprim or sulfamethoxazole.
* Documented megaloblastic anemia due to folate deficiency.
* Infants younger than 2 months (risk of kernicterus).
* Severe renal or hepatic insufficiency.
* History of drug-induced immune thrombocytopenia with prior use.
## Adverse Effects
Common: Rash, nausea, vomiting, diarrhea, anorexia.
Serious: Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hyperkalemia, hyponatremia, bone marrow suppression (anemia, leukopenia, thrombocytopenia), hepatic dysfunction, 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 levels and toxicity.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Diuretics (e.g., thiazides):** Increased risk of thrombocytopenia in elderly patients.
## Monitoring
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium).
* Complete blood count (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs).
* Fluid intake and urine output (to prevent crystalluria).
## Clinical Pearls
* Administer with food or milk to minimize gastrointestinal upset.
* Ensure adequate fluid intake to prevent crystalluria.
* Advise patients to report any rash, sore throat, or fever immediately.
* Avoid in patients with G6PD deficiency due to risk of hemolytic anemia.
* Monitor potassium levels, especially in patients with renal impairment or those taking other agents that affect potassium.
This information is intended as a quick reference. Always consult the most current prescribing information and relevant clinical guidelines for complete details and to ensure patient-specific appropriateness.
