What is the recommended dosage of trimethoprim-sulfamethoxazole (cotrimazole) for adults?

Trimethoprim-Sulfamethoxazole (Cotrimoxazole) Dosing for Adults

For most adult indications, the standard dose is one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) twice daily, with specific adjustments based on the clinical condition being treated. 1

Standard Adult Dosing by Indication

Urinary Tract Infections & Shigellosis

• One double-strength tablet every 12 hours for 10-14 days (UTI) or 5 days (shigellosis) 1
• Alternative: Two single-strength tablets every 12 hours 1

Acute Exacerbations of Chronic Bronchitis

• One double-strength tablet every 12 hours for 14 days 1

MRSA Skin and Soft Tissue Infections

• One to two double-strength tablets twice daily (320-640 mg TMP/1600-3200 mg SMZ total daily dose) 2
• This represents the higher end of dosing for more severe infections 2

Pneumocystis Pneumonia (PCP)

Treatment:

• 75-100 mg/kg sulfamethoxazole and 15-20 mg/kg trimethoprim per 24 hours, divided every 6 hours for 14-21 days 1
• For a 70 kg adult at the upper limit: 2 double-strength tablets every 6 hours 1
• For lower limit dosing (75 mg/kg), administer 75% of the upper limit dose 1

Prophylaxis:

• One double-strength tablet daily 1
• Alternative schedules: 160/800 mg three times weekly on consecutive days 3

Traveler's Diarrhea

• One double-strength tablet every 12 hours for 5 days 1

Renal Dose Adjustments

Critical consideration: Dosing must be adjusted for impaired renal function to prevent toxicity 1

• Creatinine clearance >30 mL/min: Standard dosing 1
• Creatinine clearance 15-30 mL/min: Half the usual dose 1
• Creatinine clearance <15 mL/min: Use not recommended 1

For severe renal failure requiring continued therapy, the dosage interval in hours should equal 12 times the serum creatinine level in mg/dL (maximum 48-hour interval), with therapeutic drug monitoring of trimethoprim levels 4

Important Safety Considerations

Hematologic Monitoring

• Obtain baseline complete blood count and monitor monthly for thrombocytopenia, leukopenia, and anemia 2
• Thrombocytopenia correlates with higher serum trimethoprim levels and longer treatment duration 4

Drug Interactions

• Avoid concurrent use with methotrexate at treatment doses (160/800 mg twice daily) due to risk of severe bone marrow suppression 3
• Lower prophylactic doses (160/800 mg three times weekly or 80/400 mg daily) are generally tolerated with methotrexate 3

Contraindications

• Avoid at term in pregnancy 2
• Do not use in patients with G6PD deficiency due to hemolytic anemia risk 3

Common Pitfalls

Fluid overload: The large dilution volume required for IV formulations can cause fluid overload, particularly in elderly or cardiac patients 4

Inadequate dosing for severe infections: PCP treatment requires substantially higher doses (every 6 hours) than standard bacterial infections (every 12 hours) 1

Failure to adjust for renal function: This is the most common cause of preventable toxicity, particularly thrombocytopenia 4