What is the recommended dosage of Bactrim (trimethoprim/sulfamethoxazole) for treating infections, particularly in patients with impaired renal function?

From the Guidelines

The recommended dosage of Bactrim (trimethoprim/sulfamethoxazole) for most infections is one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 10-14 days, or one regular-strength tablet (80 mg trimethoprim/400 mg sulfamethoxazole) every 12 hours. However, for patients with impaired renal function, dosage adjustments are necessary.

Key Considerations

• For those with creatinine clearance between 15-30 mL/min, the recommended dose is half the normal dose 1.
• For patients with creatinine clearance below 15 mL/min, Bactrim is generally not recommended, or the dose should be reduced to half the normal dose or an alternative agent should be used 1.

Dosing Adjustments

• Dosing should be based on the patient's weight, severity of infection, and renal function.
• Adequate hydration is important during treatment to prevent crystalluria.

Mechanism of Action

• Bactrim works by inhibiting two consecutive steps in bacterial folate synthesis - sulfamethoxazole blocks the incorporation of para-aminobenzoic acid into dihydrofolic acid, while trimethoprim inhibits dihydrofolate reductase, preventing the formation of tetrahydrofolic acid.
• This dual mechanism provides synergistic antibacterial activity but also increases the risk of adverse effects in patients with kidney dysfunction due to reduced drug clearance.

Recent Guidelines

• Recent guidelines from the American College of Physicians suggest that short-course antibiotics, including trimethoprim-sulfamethoxazole, can be effective for treating uncomplicated urinary tract infections 1.

From the FDA Drug Label

The usual adult dosage in the treatment of urinary tract infections is 1 sulfamethoxazole and trimethoprim double strength tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours for 10 to 14 days For Patients with Impaired Renal Function When renal function is impaired, a reduced dosage should be employed using the following table: Creatinine Clearance (mL/min) Recommended Dosage Regimen Above 30 Usual standard regimen 15 to 30 ½ the usual regimen Below 15 Use not recommended

The recommended dosage of Bactrim (trimethoprim/sulfamethoxazole) for treating infections is:

• 1 double strength tablet or 2 single strength tablets every 12 hours for 10 to 14 days for urinary tract infections in adults.
• For patients with impaired renal function:
  • Usual standard regimen for creatinine clearance above 30 mL/min.
  • ½ the usual regimen for creatinine clearance between 15 to 30 mL/min.
  • Use not recommended for creatinine clearance below 15 mL/min. 2

From the Research

Dosing for Bactrim DS

The recommended dosage of Bactrim (trimethoprim/sulfamethoxazole) for treating infections, particularly in patients with impaired renal function, is as follows:

• The usual dosage for adults is 1 Bactrim DS (double strength) tablet or 2 Bactrim tablets every 12 hours 3.
• For patients with impaired renal function, the dosage should be adjusted based on the creatinine clearance 4.
• The following dosages are recommended for patients with renal impairment:
  • Creatinine clearance 30-50 mL/min: 1 Bactrim DS tablet every 12 hours
  • Creatinine clearance 15-29 mL/min: 1 Bactrim DS tablet every 24 hours
  • Creatinine clearance < 15 mL/min: not recommended

Considerations for Patients with Impaired Renal Function

• Patients with impaired renal function are at increased risk of adverse outcomes, including acute kidney injury and hyperkalaemia, when treated with trimethoprim/sulfamethoxazole 4.
• The risk of adverse outcomes is higher in patients taking renin-angiotensin system blockers and potassium-sparing diuretics 4.
• Close monitoring of renal function and electrolyte levels is recommended in patients with impaired renal function who are treated with trimethoprim/sulfamethoxazole 4.

Resistance Rates and Treatment Guidelines

• Resistance rates to trimethoprim/sulfamethoxazole vary by region and can be as high as 34% 5.
• Guidelines recommend trimethoprim/sulfamethoxazole for empirical treatment of uncomplicated UTIs unless resistance rates in the community exceed 10% to 20% 3.
• Alternative antibiotics, such as fluoroquinolones or nitrofurantoin, may be considered in areas with high resistance rates or in patients with impaired renal function 3.