What is the appropriate dose of Bactrim (Trimethoprim/Sulfamethoxazole) for a patient weighing 85 kilograms?

From the Guidelines

For an 85 kg patient, the recommended dose of Bactrim (trimethoprim-sulfamethoxazole) is 1-2 double-strength (DS) tablets every 12 hours for most infections, with each DS tablet containing 160 mg trimethoprim and 800 mg sulfamethoxazole.

Standard Dosing

The standard adult dosing is typically sufficient for most infections, and the patient's weight does not directly influence the dosing in this case, as the standard dosing is not weight-based for typical infections 1.

• For more severe infections like Pneumocystis pneumonia, a weight-based approach is needed, using 15-20 mg/kg/day of the trimethoprim component divided into 3-4 doses.
• For an 85 kg patient, this would equal approximately 1,275-1,700 mg of trimethoprim daily, or about 8-11 DS tablets daily divided into 3-4 doses.

Renal Impairment Considerations

Dosing should be adjusted for renal impairment, with a 50% reduction recommended for creatinine clearance of 15-30 mL/min and avoidance if clearance is below 15 mL/min 1.

• The adjustment for renal impairment is crucial to prevent toxicity and ensure the efficacy of the treatment.

Mechanism of Action

Bactrim works by inhibiting bacterial folate synthesis at two different points in the pathway, with trimethoprim blocking dihydrofolate reductase and sulfamethoxazole inhibiting dihydropteroate synthetase.

Specific Infections

For urinary tract infections, a lower dose of 1 DS tablet twice daily for 3-14 days is typically sufficient, as indicated in the guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women 1.

• The choice of antibiotic should consider local resistance rates and the specific type of infection being treated.

From the FDA Drug Label

The recommended dose for children with urinary tract infections or acute otitis media is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days. For Patients with Impaired Renal Function When renal function is impaired, a reduced dosage should be employed using the following table: The following table is a guideline for the attainment of this dosage: Children 2 months of age or older: Weight Dose – every 12 hours lb kg Tablets 22 10 - 44 20 1 66 30 1½ 88 40 2 or 1 DS tablet

For an 85 kg patient, the dose is not explicitly stated in the provided table. However, based on the recommended dose of 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, the dose can be calculated as follows:

• Sulfamethoxazole: 40 mg/kg x 85 kg = 3400 mg per 24 hours
• Trimethoprim: 8 mg/kg x 85 kg = 680 mg per 24 hours Given in two divided doses every 12 hours, the dose would be:
• Sulfamethoxazole: 1700 mg every 12 hours
• Trimethoprim: 340 mg every 12 hours Since the exact dosage for an 85 kg patient is not provided in the table, and considering the patient is an adult, the usual adult dosage can be considered:
• 1 sulfamethoxazole and trimethoprim DS (double strength) tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours. However, the exact dosage for the patient's weight is not directly provided, and the calculation above is based on the pediatric dosage guideline. Therefore, the most conservative approach would be to consult the prescriber or a pharmacist for the exact dosage, as the provided information does not directly answer the question for an adult patient weighing 85 kg 2.

From the Research

Dosing Considerations for Bactrim (Trimethoprim/Sulfamethoxazole)

The appropriate dose of Bactrim for a patient weighing 85 kilograms is not explicitly stated in the provided studies. However, the following points can be considered:

• The standard dosing regimen for Bactrim is not provided in the studies, but it is mentioned that the dosage should be adjusted when the creatinine clearance decreases to less than 30 ml/min 3.
• In patients with renal failure, the dose of trimethoprim/sulfamethoxazole may need to be reduced, and therapeutic drug monitoring is advisable to ensure optimal dosing 4.
• The pharmacokinetics of trimethoprim and sulfamethoxazole are affected by renal dysfunction, and the drugs are primarily excreted in the urine 5, 3.
• In patients undergoing hemodialysis, 50% of the maintenance dose of trimethoprim/sulfamethoxazole should be supplemented after each dialysis session 6.

Key Points to Consider

• Renal function: The dosage of Bactrim may need to be adjusted based on the patient's renal function, particularly when the creatinine clearance is less than 30 ml/min 3.
• Patient weight: The patient's weight (85 kilograms) may be a factor in determining the appropriate dose, but this is not explicitly stated in the studies.
• Therapeutic drug monitoring: In patients with renal failure or those undergoing continuous renal replacement therapy, therapeutic drug monitoring is advisable to ensure optimal dosing 4.