IV Bactrim (Trimethoprim/Sulfamethoxazole) Dosing for Bacterial Infections
The recommended IV dose of Bactrim (trimethoprim/sulfamethoxazole) for bacterial infections in adults is 8-12 mg/kg/day (based on the trimethoprim component) divided into 4 doses. 1
Adult Dosing
- Standard IV dosing: 8-12 mg/kg/day based on trimethoprim component, divided into 4 doses
- Practical administration: Typically given as 1-2 ampules every 6 hours (each ampule contains 80 mg trimethoprim and 400 mg sulfamethoxazole)
- Alternative expression: Can be administered as 160-320 mg trimethoprim component every 6 hours
Pediatric Dosing
- Standard IV dosing: 8-12 mg/kg/day based on trimethoprim component, divided into 4 doses 1
- Important note: Doses listed are not appropriate for neonates; refer to the American Academy of Pediatrics guidelines for neonatal dosing regimens
Indication-Specific Considerations
For MRSA infections:
- For central nervous system infections: TMP 600 mg PO daily or 300-450 mg PO every 12 hours (when used in combination with vancomycin) 1
- For osteomyelitis: TMP 4 mg/kg/dose PO/IV every 8-12 hours (when used in combination with rifampin) 1
Duration of Therapy
Duration varies by infection type:
- Skin and soft tissue infections: 7-14 days 2
- Bacteremia: 14 days for uncomplicated, 4-6 weeks for complicated 2
- Osteomyelitis: 4-6 weeks 2
- Septic arthritis: 3-4 weeks 2
Administration Guidelines
- IV Bactrim should be diluted in 5% dextrose in water (D5W)
- Administer over 60-90 minutes to minimize infusion-related adverse effects
- Monitor for:
- Electrolyte abnormalities (particularly hyperkalemia)
- Renal function (adjust dosing in renal impairment)
- Bone marrow suppression (monitor CBC)
Dosage Adjustments
Renal Impairment
- CrCl 15-30 mL/min: Reduce dose by 50%
- CrCl <15 mL/min: Not recommended unless patient is on hemodialysis
Common Pitfalls and Caveats
Fluid overload risk: IV formulation requires significant dilution volume, which may be problematic in patients with heart failure or renal impairment 3
Monitoring requirements: Regular monitoring of complete blood count is essential, especially during prolonged therapy, as thrombocytopenia has been associated with higher serum TMP levels and longer treatment duration 3
Resistance concerns: While resistance to trimethoprim among enterobacteria is increasing, there is currently no conclusive evidence of a rapid increase following introduction of trimethoprim alone for urinary tract infections 4
Adverse effects: At therapeutic dosages, Bactrim is generally well-tolerated, but watch for skin rashes and gastrointestinal upset 4
Drug interactions: Bactrim may increase levels of warfarin, phenytoin, and methotrexate; monitor closely when co-administered
Contraindications: Avoid in patients with sulfa allergy, G6PD deficiency, severe hepatic or renal impairment, or megaloblastic anemia due to folate deficiency
By following these dosing guidelines and monitoring parameters, IV Bactrim can be effectively and safely administered for various bacterial infections.