Potential protein-binding displacement interactions with perampanel: An in vitro analysis

Plasma protein binding and effects on volume of distribution and pharmacologically active, circulating-drug concentrations are complex issues. Protein-binding displacement often underlies drug-drug interactions. Perampanel is a once-daily oral anti-seizure drug for focal seizures and primary generalized tonic-clonic seizures. Perampanel is also indicated for monotherapy use for focal seizures in the United States. Perampanel is extensively but slowly metabolized via CYP3A4. Its elimination t_½ is about 100 h, and it displays substantial plasma protein binding (>95%). Here, we examine perampanel's potential to displace highly bound anti-seizure drugs and the ability of warfarin, a standard highly protein-bound drug, to displace perampanel. Protein binding of perampanel, phenytoin, valproate, and warfarin was assessed using equilibrium dialysis. Plasma samples containing each compound were dialyzed against phosphate buffered saline. For phenytoin, valproate, and warfarin, plasma samples were also dialyzed in the presence of perampanel. After 24 h equilibrium dialysis, amounts of test compounds were analyzed to calculate plasma protein binding. At clinically relevant concentrations, perampanel did not displace other highly bound drugs or vice versa. Protein-binding displacement may confound therapeutic drug monitoring of extensively protein-bound medications. Without empirical data, clinicians might be concerned that addition of perampanel could alter unbound concentrations of other medications, resulting in adverse effects. Our data indicate perampanel has low potential for drug interactions resulting from protein-binding displacement.