Sulfamethoxazole-Trimethoprim (Sulfatrim) Dosage and Treatment Duration for Adult Bacterial Infections
The standard adult dosage of Sulfamethoxazole-Trimethoprim (Sulfatrim) for bacterial infections is one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) taken orally twice daily for 10-14 days for urinary tract infections, 5 days for shigellosis, and 14 days for acute exacerbations of chronic bronchitis. 1
Dosage by Infection Type
Urinary Tract Infections
- One double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) or two single-strength tablets every 12 hours for 10-14 days 1
- Clinical and microbiological cure rates for UTIs are 90-100% when the pathogen is susceptible to trimethoprim-sulfamethoxazole 2
- Three-day regimens have shown comparable efficacy to longer courses for uncomplicated UTIs, with clinical cure rates of 90% 2
Shigellosis
- One double-strength tablet or two single-strength tablets every 12 hours for 5 days 1
Acute Exacerbations of Chronic Bronchitis
- One double-strength tablet or two single-strength tablets every 12 hours for 14 days 1
Pneumocystis jiroveci Pneumonia
- Higher doses are required: 75-100 mg/kg sulfamethoxazole and 15-20 mg/kg trimethoprim per 24 hours divided into equal doses given every 6 hours for 14-21 days 1
Skin and Soft Tissue Infections
- One to two double-strength tablets twice daily orally 2
- Duration of approximately 7 days, depending on clinical response 2
Traveler's Diarrhea
- One double-strength tablet or two single-strength tablets every 12 hours for 5 days 1
Dosage Adjustments
Renal Impairment
- Creatinine clearance >30 mL/min: Standard regimen
- Creatinine clearance 15-30 mL/min: Half the usual regimen
- Creatinine clearance <15 mL/min: Not recommended 1
Elderly Patients
- Elderly patients may have higher peak concentrations and larger area under the curve for trimethoprim component 3
- Monitor for side effects as plasma drug concentrations may be 2-3 times higher than in younger adults after several days of treatment 3
Efficacy and Considerations
- Trimethoprim-sulfamethoxazole remains highly effective for UTIs when the rate of resistance is <20% 2
- Clinical cure rates of 93-100% have been reported for UTIs when the pathogen is susceptible 2
- Bacterial cure rates of 91-100% have been reported 2
- Single-dose therapy has been studied for uncomplicated UTIs with 93% eradication rate, but is not FDA-approved for this indication 4
Common Side Effects and Monitoring
- Common side effects include rash, urticaria, nausea, vomiting, and hematologic abnormalities 2
- Side effect rates of 24-38% have been reported with standard 10-day regimens 4, 2
- Once-daily dosing regimens may improve compliance compared to twice-daily dosing 5
Important Caveats
- Resistance patterns should be considered before prescribing, as efficacy drops significantly against resistant organisms (41-54% clinical cure rate vs 84-88% for susceptible organisms) 2
- Not recommended for children under 2 months of age 1
- Alternative therapies should be considered for patients with sulfa allergies
- Fluoroquinolones may have fewer adverse reactions (17% vs 32%) with similar efficacy 6
Remember that treatment duration should be completed as prescribed even if symptoms resolve earlier to prevent relapse and the development of resistant organisms.