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# Septra (Trimethoprim/Sulfamethoxazole)
## Overview
Septra is a combination antibiotic containing trimethoprim and sulfamethoxazole in a fixed ratio of 1:5. It is a broad-spectrum antibiotic effective against many Gram-positive and Gram-negative bacteria.
## Primary Indications
* Urinary tract infections (UTIs)
* Acute otitis media
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
## Adult Dosing
* **Urinary Tract Infections (Uncomplicated):** 1 double strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) twice daily for 3 days.
* **Urinary Tract Infections (Complicated) and Other Infections:** 1 DS tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours. Duration varies by indication.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, for 14-21 days. This is typically administered as 2 DS tablets every 8 hours or 1 DS tablet every 6 hours.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 1 DS tablet once daily, or 1 DS tablet three times a week.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **Urinary Tract Infections and Shigellosis:** 8 mg/kg/day of trimethoprim, divided into two doses. This is typically administered as 1 DS tablet twice daily for children over 12 years. For younger children, doses are calculated based on weight.
* **Acute Otitis Media:** 8 mg/kg/day of trimethoprim, divided into two doses, for 10 days.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day of trimethoprim, divided into 3-4 doses, for 14-21 days.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 5 mg/kg/day of trimethoprim, divided into two doses, given once daily for 3 days a week, or 10 mg/kg/day every other day.
*Note: Specific pediatric dosing may vary based on local protocols and the specific formulation used.*
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer at 75% of the standard dose.
* CrCl < 15 mL/min: Avoid use or administer at 50% of the standard dose every other day.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic impairment.
* History of drug-induced immune thrombocytopenia with either component.
## Adverse Effects
* **Common:** Nausea, vomiting, rash, pruritus, hyperkalemia.
* **Serious:** Stevens-Johnson syndrome, toxic epidermal necrolysis, exfoliative dermatitis, anaphylaxis, severe hematologic reactions (e.g., aplastic anemia, agranulocytosis, thrombocytopenia), pseudomembranous colitis, hepatic necrosis, crystalluria.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose as needed.
* **ACE inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia. Monitor potassium levels.
* **Methotrexate:** Increased risk of methotrexate toxicity due to displacement from plasma protein binding and inhibition of dihydrofolate reductase.
* **Cyclosporine:** Increased cyclosporine levels, potentially leading to nephrotoxicity.
* **Potassium Supplements/Potassium-Containing Salt Substitutes:** Increased risk of hyperkalemia.
## Monitoring
* Renal function (BUN, creatinine).
* Complete blood counts (CBC) with differential, especially with prolonged therapy or in patients with G6PD deficiency.
* Electrolytes, particularly potassium.
* Liver function tests.
* Signs of hypersensitivity reactions.
* Signs of crystalluria (ensure adequate fluid intake).
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Sulfonamides can displace bilirubin from albumin; use with caution in neonates and in patients with hyperbilirubinemia.
* Photosensitivity is common; advise patients to use sun protection.
* Discontinue immediately if a rash appears.
* Trimethoprim can cause reversible elevations in serum creatinine without a true decrease in glomerular filtration rate (inhibition of tubular secretion).
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines before making clinical decisions.*
