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Effect of continuous hemofiltration on phenytoin elimination
1Department of Pharmacy Practice, University of Illinois at Chicago 60612.
Therapeutic Drug Monitoring
|February 1, 1994
Summary
Continuous hemofiltration can remove significant amounts of phenytoin in critically ill patients with acute renal failure. Dosage adjustments and drug monitoring are crucial to maintain therapeutic phenytoin levels.
Area of Science:
- Pharmacology
- Nephrology
- Critical Care Medicine
Background:
- Phenytoin is a key anticonvulsant for critically ill patients.
- Acute renal failure (ARF) necessitates renal replacement therapy, such as continuous hemofiltration (CHF).
- The impact of CHF on phenytoin pharmacokinetics in ARF patients is not well-defined.
Observation:
- Phenytoin concentrations in ultrafiltrate closely mirrored free serum concentrations.
- The ratio of ultrafiltrate to arterial drug concentration reflected the percentage of free serum drug.
- Phenytoin removal rates by CHF ranged from 0.32 to 0.78 mg/h.
Findings:
- Phenytoin removal during CHF is influenced by free drug concentration, total serum concentration, and ultrafiltration flow rate.
- At high ultrafiltration rates, CHF can significantly remove phenytoin, especially when protein binding is reduced in ARF.
- Low ultrafiltration rates result in minimal phenytoin removal relative to daily doses.
Implications:
- Clinically significant phenytoin removal by CHF may necessitate higher daily doses to achieve therapeutic efficacy.
- Close serum phenytoin concentration monitoring is essential for optimizing dosage regimens in patients undergoing CHF.
- This highlights the importance of considering extracorporeal therapies when managing drug therapy in ARF.