Ampicillin/Sulbactam Dosing for a 66 kg Adult Man
For a 66 kg adult man with normal renal function, administer ampicillin/sulbactam 3 g (2 g ampicillin/1 g sulbactam) intravenously every 6 hours. 1
Standard Dosing Regimen
The FDA-approved dosing range for adults with normal renal function is 1.5 g to 3 g every 6 hours, where this represents the total of ampicillin plus sulbactam content 1. This corresponds to:
- 1.5 g dose = 1 g ampicillin + 0.5 g sulbactam
- 3 g dose = 2 g ampicillin + 1 g sulbactam 1
The total daily dose of sulbactam should not exceed 4 grams per day 1, which means the maximum regimen is 3 g every 6 hours (providing 4 g sulbactam daily).
Administration Guidelines
- Administer by slow intravenous injection over at least 10-15 minutes 1
- Alternatively, dilute in 50-100 mL of compatible diluent and infuse over 15-30 minutes 1
- For serious infections, consider extended infusion of 4 hours to optimize pharmacokinetic/pharmacodynamic properties, particularly when treating organisms with higher MICs 2
Dosing Rationale
The 3 g every 6 hours regimen is appropriate for this patient because:
- For complicated intra-abdominal infections, the recommended baseline is 3.375 g every 6 hours for piperacillin/tazobactam 3, and ampicillin/sulbactam at 3 g every 6 hours provides comparable coverage
- Pediatric dosing guidelines recommend 200 mg/kg/day of ampicillin component (divided every 6 hours) 4, which for a 66 kg adult would approximate 13.2 g ampicillin daily—the 3 g every 6 hours regimen provides 8 g ampicillin daily, which is reasonable for most adult infections
- Pharmacokinetic studies demonstrate adequate tissue penetration and bacterial killing with standard dosing in patients with normal renal function 2
Duration of Therapy
- Limit treatment to 4-7 days for most infections unless source control is inadequate 3
- The course of intravenous therapy should not routinely exceed 14 days 1
Critical Considerations
Weight-Based Dosing Not Required
Unlike pediatric patients where dosing is weight-based (300 mg/kg/day total drug) 1, adult dosing uses fixed doses regardless of weight for patients weighing 40 kg or more 1. At 66 kg, this patient receives standard adult dosing.
Renal Function Monitoring
This dosing assumes normal renal function (creatinine clearance ≥30 mL/min) 1. If renal impairment develops:
- CrCl 15-29 mL/min: Reduce to 1.5-3 g every 12 hours 1
- CrCl 5-14 mL/min: Reduce to 1.5-3 g every 24 hours 1
- Hemodialysis patients: Dose every 24 hours, administered after dialysis 5
Infection-Specific Considerations
For β-lactamase-producing enterococcal endocarditis, ampicillin-sulbactam 12 g/24 hours (3 g every 6 hours) in 4 equally divided doses for 6 weeks is recommended 4, demonstrating that the 3 g every 6 hours regimen is appropriate for serious infections.
For Acinetobacter baumannii infections with MIC ≤4 mg/L, sulbactam 9-12 g/day in 3-4 divided doses is recommended 4, which corresponds to ampicillin/sulbactam 4.5-6 g every 6-8 hours (higher than standard dosing).
Common Pitfalls to Avoid
- Do not exceed 4 g/day of sulbactam to avoid potential toxicity 1
- Do not use intramuscular administration as the safety and efficacy have not been established in adults for serious infections 1
- Avoid underdosing in serious infections—the 1.5 g dose is inadequate for most hospitalized patients with severe infections 2
- Monitor for renal function changes as both ampicillin and sulbactam are primarily renally eliminated (71% and 78%, respectively) 6