Bactrim 800-160 Suspension Dosing for Adults with Normal Renal Function
For a 77.57 kg adult with normal renal function, the standard dose of Bactrim (trimethoprim-sulfamethoxazole) 800-160 mg suspension is 20 mL (4 teaspoonfuls) every 12 hours, which provides 800 mg sulfamethoxazole and 160 mg trimethoprim per dose. 1
Standard Adult Dosing Regimen
The FDA-approved dosing for most adult indications is 800 mg sulfamethoxazole/160 mg trimethoprim (equivalent to 20 mL or 4 teaspoonfuls of suspension) administered every 12 hours. 1
This dosing applies to urinary tract infections (10-14 days), acute exacerbations of chronic bronchitis (14 days), shigellosis (5 days), and traveler's diarrhea (5 days). 1
For pertussis treatment as an alternative agent, the CDC recommends trimethoprim 320 mg per day with sulfamethoxazole 1,600 mg per day in 2 divided doses for 14 days, which translates to the same 20 mL twice daily dosing. 2
Weight-Based Considerations
While the standard adult dose is fixed at 800-160 mg twice daily, weight-based dosing is primarily used for pediatric patients and specific severe infections. 1
For your 77.57 kg patient, the standard adult dose of 20 mL (800-160 mg) twice daily is appropriate and does not require weight-based adjustment for routine indications. 1
Special Dosing Scenarios
For Pneumocystis jirovecii Pneumonia (PCP)
Treatment requires significantly higher doses: 75-100 mg/kg/day of sulfamethoxazole with 15-20 mg/kg/day of trimethoprim, divided every 6 hours for 14-21 days. 1
For a 77.57 kg patient, this would be approximately 40-50 mL (8-10 teaspoonfuls) every 6 hours for treatment doses. 1
Prophylaxis dosing is 20 mL (4 teaspoonfuls) daily. 1
For MRSA Infections
The IDSA recommends 3.5-4.0 mg/kg/dose of trimethoprim component every 8-12 hours for bone and joint infections or CNS infections. 2
For a 77.57 kg patient, this translates to approximately 5 mg/kg/dose every 8-12 hours of the trimethoprim component for serious MRSA infections. 2
Renal Function Adjustments
Your patient has normal renal function, so no dose adjustment is needed. 1
If creatinine clearance were 15-30 mL/min, reduce to half the usual dose; if below 15 mL/min, use is not recommended. 1
Important Clinical Considerations
TMP-SMX should be used with caution in older adults due to higher incidence of severe adverse events, including Stevens-Johnson syndrome, toxic epidermal necrolysis, blood dyscrasias, and hepatic necrosis. 2
Instruct patients to maintain adequate fluid intake to prevent crystalluria and renal stones. 2
Monitor for drug interactions with methotrexate, oral anticoagulants, antidiabetic agents, thiazide diuretics, and anticonvulsants. 2
Gastrointestinal adverse effects and hypersensitivity skin reactions are common. 2