What is the appropriate dose of Bactrim (Trimethoprim/Sulfamethoxazole) for an 85 kg patient receiving intravenous (IV) administration?

From the FDA Drug Label

The recommended dosage for treatment of patients with documented Pneumocystis jirovecii pneumonia is 75 to 100 mg/kg sulfamethoxazole and 15 to 20 mg/kg trimethoprim per 24 hours given in equally divided doses every 6 hours for 14 to 21 days.

For an 85 kg patient, the dose would be:

• 75 mg/kg sulfamethoxazole: 75 mg/kg x 85 kg = 6375 mg per 24 hours
• 15 mg/kg trimethoprim: 15 mg/kg x 85 kg = 1275 mg per 24 hours Given in equally divided doses every 6 hours, the dose would be:
• 6375 mg / 4 = 1593.75 mg sulfamethoxazole per dose
• 1275 mg / 4 = 318.75 mg trimethoprim per dose However, the provided drug label does not explicitly state the IV administration dosage for an 85 kg patient. The information provided is for oral suspension. The FDA drug label does not answer the question.

From the Research

For a patient weighing 85 kg requiring intravenous Bactrim (trimethoprim-sulfamethoxazole), the recommended dose is 5-20 mg/kg/day of the trimethoprim component, divided into 2-4 doses, depending on the severity of infection.

Dosing Considerations

For a moderate infection, a typical dose would be 10 mg/kg/day, which equals 850 mg of trimethoprim daily for this patient. Since Bactrim IV comes as a solution containing 16 mg trimethoprim and 80 mg sulfamethoxazole per mL, this patient would need approximately 53 mL daily (divided into doses).

Administration and Monitoring

The medication should be administered over 60-90 minutes to minimize vein irritation. Monitor renal function, electrolytes, and complete blood count during therapy as Bactrim can cause hyperkalemia, nephrotoxicity, and bone marrow suppression. Ensure adequate hydration during treatment to prevent crystalluria.

Special Considerations

Dosage adjustment is necessary for patients with renal impairment, with frequency reduction recommended for creatinine clearance below 30 mL/min. The most recent and highest quality study 1 supports the use of trimethoprim-sulfamethoxazole as an effective treatment for urinary tract infections, but does not provide specific dosing recommendations for intravenous administration. However, based on the available evidence, the recommended dose range of 5-20 mg/kg/day is appropriate for most patients.

Key Points to Consider

• The dose of Bactrim should be adjusted based on the severity of the infection and the patient's renal function.
• The medication should be administered over a period of 60-90 minutes to minimize vein irritation.
• Monitoring of renal function, electrolytes, and complete blood count is necessary during therapy.
• Adequate hydration is essential to prevent crystalluria.
• Dosage adjustment is necessary for patients with renal impairment.