Development and Use of an Ex-Vivo In-Vivo Correlation to Predict Antiepileptic Drug Clearance in Patients Undergoing Continuous Renal Replacement Therapy.

Objectives: Results from previous ex-vivo continuous renal replacement therapy (CRRT) models have successfully demonstrated similar extraction coefficients (EC) identified from in-vivo clinical trials. The objectives of this study are to develop an ex-vivo in-vivo correlation (EVIVC) model to predict drug clearance for commonly used antiepileptics and to evaluate similarity in drug extraction across different CRRT modalities to extrapolate dosing recommendations.

Methods: Levetiracetam, lacosamide, and phenytoin CRRT clearance was evaluated using the Prismaflex CRRT system and M150 hemodiafilters using an albumin containing normal saline (ALB-NS) vehicle with 3 different albumin concentrations (2 g/dL, 3 g/dL, and 4 g/dL) and a human plasma vehicle at 3 different effluent flow rates (1 L/hr, 2 L/hr, and 3 L/hr). Blood and effluent/dialysate concentrations were collected after circuit priming. ECs were calculated for each drug, modality, vehicle, and experimental arm combination.

Results: The calculated average EC for levetiracetam and lacosamide was approximated to the fraction unbound from plasma protein. Human plasma and ALB-NS vehicles demonstrated adequate prediction of in-vivo CRRT clearance. Geometric mean ratios indicated similarity in extraction coefficients when comparing between hemofiltration and hemodiafiltration modalities and between filtration and dialysis modalities at effluent flow rates ≤ 2L/hr. Evaluation of phenytoin provided inconsistent findings with regards to extraction coefficient similarity across different CRRT modalities.

Conclusion: The findings indicate that an ex-vivo study can be used as a surrogate to predict in-vivo levetiracetam and lacosamide clearance in patients receiving CRRT.