A Physiologically Based Pharmacokinetic Model for Optimally Profiling Lamotrigine Disposition and Drug-Drug Interactions.

Background And Objectives: Lamotrigine (Lamictal) is a broad-spectrum antiepileptic drug available in both immediate-(IR) and extended-release (XR) formulations. Here, we present a new physiologically based pharmacokinetic (PBPK) model for IR and XR formulations of lamotrigine to predict disposition in adults and children, plus drug-drug interactions (DDIs).

Methods: Models for lamotrigine IR and XR formulations were constructed using a Simcyp Simulator. Concentration-time profiles were simulated for lamotrigine IR single (S) and steady-state (SS) doses ranging from 25 to 200 mg in adults, as well as 2 mg/kg (S), and 7.7-9.4 mg/kg (SS) in children aged between 4 and 17 years. Lamotrigine XR profiles were simulated for S and SS doses ranging from 250 to 400 mg. DDI prediction with lamotrigine was simulated in adults with enzyme-inducing drugs, rifampin (rifampicin) and ritonavir, as well as the enzyme inhibitor, valproic acid.

Results: The lamotrigine model predicted adult area-under-the-curve (AUC) and peak plasma concentration (C) results for IR S within 35% of observed data; lamotrigine IR SS dosing was within 10% and 30% of observed data, respectively. Pediatric lamotrigine IR S AUC and C values were within 10% and 15% of observed data, respectively. AUC and C values for lamotrigine XR S simulated in adults were within 20% of observed data; similarly lamotrigine XR SS parameters were within 10%. Concerning DDI simulation in adults, predicted-to-observed lamotrigine AUC ratios [AUC/AUC] were within 15% for ritonavir and rifampin, and 20% for valproic acid.

Conclusions: Our developed PBPK lamotrigine profile accurately predicts DDIs and lamotrigine IR/XR formulation disposition in adults and children. This PBPK model will be helpful in designing future DDI studies for co-administration of lamotrigine with other drugs and in designing individualized patient dosing regimens.