Ampicillin/Sulbactam (Unasyn) Dosage Adjustment for Renal Impairment
For patients with renal impairment, Unasyn (Ampicillin/Sulbactam) should be administered less frequently while maintaining the standard dose of 1.5-3g per administration, with specific frequency adjustments based on creatinine clearance levels. 1
Dosage Adjustment Guidelines
The FDA-approved dosing recommendations for Unasyn in renal impairment are as follows:
| Creatinine Clearance (mL/min/1.73m²) | Half-Life (Hours) | Recommended Dosage |
|---|---|---|
| ≥30 | 1 | 1.5-3g every 6-8h |
| 15-29 | 5 | 1.5-3g every 12h |
| 5-14 | 9 | 1.5-3g every 24h |
Key Principles of Dosing
- Maintain standard dose: The individual dose should remain 1.5-3g (representing 1-2g ampicillin plus 0.5-1g sulbactam) 1
- Adjust frequency: The dosing interval should be extended as renal function declines 1
- Ratio remains constant: The elimination kinetics of both ampicillin and sulbactam are similarly affected by renal impairment, so the ratio of the two components remains constant regardless of renal function 1
Calculating Creatinine Clearance
When only serum creatinine is available, use the following formula to estimate creatinine clearance:
For males:
CrCl = [Weight (kg) × (140 - age)] ÷ [72 × serum creatinine]For females:
CrCl = 0.85 × [Weight (kg) × (140 - age)] ÷ [72 × serum creatinine]Clinical Considerations
- The serum creatinine should represent a steady state of renal function 1
- Total daily sulbactam dose should not exceed 4g, even in patients with normal renal function 1
- For patients on hemodialysis, administer the dose after dialysis to avoid premature removal of the drug
Common Pitfalls to Avoid
- Reducing the individual dose: Unlike some antibiotics that require dose reduction, Unasyn requires frequency adjustment while maintaining the standard dose per administration to ensure adequate peak concentrations
- Ignoring changing renal function: Hospitalized patients often experience changes in renal function, requiring ongoing monitoring and potential dosage adjustments
- Using incorrect estimation methods: Using the wrong formula for estimating creatinine clearance can lead to inappropriate dosing
This approach to dosing Unasyn in renal impairment aligns with the general principle that many beta-lactam antibiotics require extended intervals rather than dose reductions to maintain efficacy while preventing toxicity in renal impairment.