What is the adult dose of Bactrim (sulfamethoxazole and trimethoprim) for an uncomplicated urinary tract infection (UTI)?

Adult Dosage of Bactrim for Uncomplicated UTI

For uncomplicated urinary tract infections in adults, the recommended dosage of Bactrim (sulfamethoxazole and trimethoprim) is one double-strength tablet (160/800 mg) or two regular-strength tablets (80/400 mg) taken orally every 12 hours for 3 days. 1, 2, 3

Dosing Recommendations

• Standard adult dose: 160 mg trimethoprim/800 mg sulfamethoxazole (one double-strength tablet) twice daily for 3 days 3
• Duration: 3-day regimen is sufficient for uncomplicated UTIs in women 3
• Men with UTI: 160 mg trimethoprim/800 mg sulfamethoxazole twice daily for 7 days (longer duration needed) 3
• Renal impairment adjustment:
  • CrCl >30 mL/min: Standard regimen
  • CrCl 15-30 mL/min: Half the usual regimen
  • CrCl <15 mL/min: Not recommended 1, 2

Efficacy and Considerations

• Early clinical cure rates with trimethoprim-sulfamethoxazole range from 90-100% when the pathogen is susceptible 3
• Bacterial cure rates are similarly high at 91-100% for susceptible organisms 3
• Treatment efficacy significantly decreases when the infecting organism is resistant to trimethoprim-sulfamethoxazole (clinical cure drops to 41-54%) 3

Important Caveats

• Local resistance patterns: Trimethoprim-sulfamethoxazole should only be used as empiric therapy when local E. coli resistance is <20% 3
• Contraindications: Not recommended in the last trimester of pregnancy 3
• Adverse effects: Common side effects include rash, urticaria, nausea, vomiting, and hematologic abnormalities 3
• Alternative agents: If trimethoprim-sulfamethoxazole cannot be used due to resistance or contraindications, consider:
  • Nitrofurantoin 100 mg twice daily for 5 days
  • Fosfomycin 3 g single dose
  • Pivmecillinam 400 mg three times daily for 3-5 days 3

Treatment Algorithm

1. First step: Determine if patient has risk factors for resistant organisms or complicated UTI
2. If uncomplicated UTI and local resistance <20%: Use trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days 3
3. If resistance concerns or contraindications: Select an alternative agent from the list above 3
4. If symptoms persist after treatment: Obtain urine culture and susceptibility testing; assume the organism is resistant to the initial agent and select an alternative based on susceptibility 3

Remember that treatment failure or recurrent symptoms within 2 weeks of completing therapy warrant urine culture and selection of an alternative agent, typically for a 7-day course 3.