Ampicillin IV Dosing in Hemodialysis Patients
For patients on hemodialysis, administer ampicillin 2 grams IV every 24 hours, given immediately after each dialysis session on dialysis days.
Dosing Regimen
- Standard dose: 2 grams IV every 24 hours for patients with end-stage renal disease on maintenance hemodialysis 1
- Timing: Administer the dose after hemodialysis is completed to prevent drug removal during dialysis and ensure full therapeutic benefit 1
- For patients with severe renal failure (creatinine clearance 7-30 mL/min) not yet on dialysis, reduce frequency to every 12 hours 1
Pharmacokinetic Rationale
The dosing adjustment is necessary because:
- Ampicillin's terminal half-life increases dramatically from ~1 hour in normal renal function to approximately 17.4 hours in hemodialysis patients (off dialysis) 1
- During a 4-hour hemodialysis session, approximately 35% of the ampicillin dose is removed 1
- Hemodialysis approximately doubles ampicillin clearance, reducing the half-life to about 2.2-2.3 hours during the dialysis period 1, 2
- A slight rebound in serum concentrations occurs after hemodialysis as the drug redistributes from tissues 1
Critical Timing Considerations
Post-dialysis administration is essential because:
- Giving the dose before or during dialysis results in significant drug loss (30-35% removal) and potential underdosing 1, 3
- Post-dialysis dosing facilitates directly observed therapy and ensures medication adherence 4
- This timing principle applies across all dialyzable medications in hemodialysis patients 4
Important Caveats
- Extended daily dialysis (EDD): The standard hemodialysis dosing regimen may result in significant underdosing in patients undergoing EDD, as the elimination half-life can be as short as 1.5 hours with this modality 5. These patients may require more frequent dosing or higher doses.
- Loading dose: The initial loading dose of 2 grams does not require adjustment based on renal function 4
- Monitoring: While routine therapeutic drug monitoring is not typically performed for ampicillin, consider clinical response monitoring, especially in severe infections 4
Practical Application
For a typical thrice-weekly hemodialysis schedule (Monday-Wednesday-Friday):
- Give 2 grams IV immediately after dialysis on dialysis days
- Give 2 grams IV every 24 hours on non-dialysis days
- Maintain the same milligram dose rather than reducing it, as this preserves antibacterial efficacy 4