What is the dosage and administration of IV Bactrim (trimethoprim/sulfamethoxazole) for treating bacterial infections?

IV Bactrim (Trimethoprim-Sulfamethoxazole) Dosing

For IV trimethoprim-sulfamethoxazole, administer 8-12 mg/kg/day (based on the trimethoprim component) divided into either 4 doses IV or 2 doses for most bacterial infections, with infusion over 60-90 minutes. 1

Standard Adult Dosing

• Skin and soft tissue infections (SSTI): 1-2 double-strength tablets equivalent IV twice daily, which translates to 8-12 mg/kg/day based on trimethoprim component in 2-4 divided doses 1

• MRSA infections: The same dosing applies - 8-12 mg/kg/day (trimethoprim component) in either 4 divided doses IV or 2 divided doses 1

• CNS infections (meningitis, brain abscess): Higher dosing at 5 mg/kg/dose IV every 8-12 hours (approximately 10-15 mg/kg/day) 1

Pediatric Dosing

• Standard infections: 8-12 mg/kg/day (based on trimethoprim component) in either 4 divided doses IV or 2 divided doses 1

• Severe infections: May use up to 8-12 mg/kg/day divided every 6-8 hours 1

Critical Administration Requirements

IV Bactrim must be diluted in 5% dextrose in water and infused over 60-90 minutes - never give as rapid infusion or bolus injection. 2

• Do not mix with other drugs or solutions 2
• Rapid infusion can cause severe adverse reactions 2

Renal Dose Adjustment

For patients with renal impairment, reduce the dosage and extend the dosing interval. 2, 3

• In renal failure, the dosage interval (in hours) should be increased to 12 times the serum creatinine level (mg/dL), with a maximum interval of 48 hours 3
• Monitor serum trimethoprim concentrations in severe renal failure 3

Loading Dose Consideration

• For severe infections, a loading dose of 250 mg trimethoprim/1,250 mg sulfamethoxazole per m² can be given, followed by maintenance doses of 150 mg trimethoprim/750 mg sulfamethoxazole per m² every 8 hours in children ≤10 years or every 12 hours in adults with normal renal function 3

Common Pitfalls

• Avoid underdosing: Recent evidence suggests that low-dose regimens (8-12 mg/kg/day) achieve similar clinical success to high-dose regimens (>12 mg/kg/day) for pneumonia, but ensure you reach at least the minimum threshold 4

• Monitor for adverse effects: Watch for thrombocytopenia (associated with higher serum levels and longer treatment duration), hyperkalemia, and acute kidney injury 3, 4

• Fluid overload: The large dilution volume required for IV administration can cause fluid overload, particularly in vulnerable patients 3

Duration of Therapy

• SSTI: Typically 7-21 days depending on severity and clinical response 1
• Osteomyelitis: >6 weeks 1
• Septic arthritis: 3-4 weeks 1