What is the recommended dosage and treatment duration for Cotrimoxazole (trimethoprim/sulfamethoxazole)?

Cotrimoxazole (Trimethoprim/Sulfamethoxazole) Dosing and Treatment Duration

For adults with uncomplicated urinary tract infections, the recommended dosage of cotrimoxazole is one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) orally twice daily for 3 days, while for pyelonephritis, the same dosage should be continued for 14 days. 1

Standard Dosing Recommendations by Indication

Urinary Tract Infections

• Uncomplicated cystitis in adults: One double-strength tablet (160/800 mg) twice daily for 3 days 1
• Complicated UTI/Pyelonephritis in adults: One double-strength tablet (160/800 mg) twice daily for 14 days 1
• UTI in children: 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per 24 hours, divided into two doses every 12 hours for 10 days 2

Respiratory Infections

• Pertussis (whooping cough): 1
  • Adults: 160 mg trimethoprim/800 mg sulfamethoxazole twice daily for 14 days
  • Children >2 months: 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per day in 2 divided doses for 14 days
  • Contraindicated in infants <2 months

Pneumocystis Pneumonia

• Treatment: 15-20 mg/kg trimethoprim and 75-100 mg/kg sulfamethoxazole per 24 hours in divided doses every 6 hours for 14-21 days 2
• Prophylaxis: One double-strength tablet daily for adults 2

Skin and Soft Tissue Infections

• Hordeolum cellulitis: One double-strength tablet twice daily for 7-10 days 3

Gastrointestinal Infections

• Shigellosis: One double-strength tablet twice daily for 5 days 2
• Traveler's diarrhea: One double-strength tablet twice daily for 5 days 2

Dosage Adjustments

Renal Impairment

• Creatinine clearance >30 mL/min: Standard regimen 2
• Creatinine clearance 15-30 mL/min: Half the usual regimen 2, 4
• Creatinine clearance <15 mL/min: Not recommended 2

Treatment Duration Considerations

Treatment duration varies by indication:

• Acute uncomplicated cystitis: 3 days 1
• Pyelonephritis: 14 days 1
• Pertussis: 14 days 1
• Pneumocystis pneumonia: 14-21 days 2
• Skin infections: 7-10 days 3
• Gastrointestinal infections: 5 days 2

Efficacy Considerations

• Clinical cure rates for UTIs with cotrimoxazole range from 79-100% when the pathogen is susceptible 1
• Significantly lower cure rates (41-54%) are observed when the pathogen is resistant to cotrimoxazole 1
• For pyelonephritis, microbiological cure rates are approximately 89% when the pathogen is susceptible 1

Important Contraindications and Precautions

• Contraindicated in:

  • Infants <2 months (risk of kernicterus) 1
  • Pregnant women in third trimester 1, 3
  • Nursing mothers 1
  • Patients with severe renal impairment (CrCl <15 mL/min) 2
  • Known hypersensitivity to sulfonamides or trimethoprim 1

• Use with caution in:

  • Patients with impaired hepatic function 1
  • Patients with folate deficiency 1
  • Patients with blood dyscrasias 1
  • Elderly patients (higher risk of severe adverse events) 1

Common Adverse Effects

• Gastrointestinal effects (nausea, vomiting, diarrhea) 1, 3
• Hypersensitivity skin reactions 1, 3
• Rarely: Stevens-Johnson syndrome, toxic epidermal necrolysis, blood dyscrasias, hepatic necrosis 1, 3

Clinical Pearls

• Maintain adequate fluid intake during treatment to prevent crystalluria and renal stones 1
• Consider alternative agents when local resistance rates to cotrimoxazole exceed 20% for UTIs 1
• For severe infections, consider an initial dose of a long-acting parenteral antimicrobial (e.g., ceftriaxone 1g) before starting oral cotrimoxazole 1
• Monitor for improvement within 48-72 hours; if no improvement is seen, consider resistance or need for drainage if abscess formation has occurred 3