Effects of Renal Impairment on the Pharmacokinetics of Once-Daily Amantadine Extended-Release Tablets

BackgroundAn extended-release formulation of amantadine (Osmolex ER (TM), Osmotica Pharmaceutical US LLC) was approved in February 2018 to treat Parkinson's disease and drug-induced extrapyramidal reactions in adults.ObjectivesTo determine the pharmacokinetic profile of extended-release amantadine in subjects with varying degrees of renal impairment.MethodsAdults with normal renal function (creatinine clearance > 89mL/min/1.73m(2)), moderate renal impairment (creatinine clearance 30-59mL/min/1.73m(2)), or severe renal impairment (estimated glomerular filtration rate < 30mL/min/1.73m(2)) received a single 129-mg dose (160mg amantadine hydrochloride) of extended-release amantadine. Blood and urine samples for pharmacokinetic analysis were taken at scheduled intervals. A two-compartment pharmacokinetic population model was employed to determine optimum extended-release amantadine dosing in subjects with renal impairment.ResultsFollowing a single oral dose of the 129-mg extended-release amantadine tablet, amantadine plasma concentration increased slowly, reaching a peak at approximately 11h. Amantadine elimination was reduced in subjects with renal impairment. Renal clearance decreased from 10,965 to 2618mL/h in subjects with severe renal impairment compared to those with normal renal function. Pharmacokinetic modeling and simulation methods were used to recommend the oral administration of 129-mg extended-release amantadine tablets at intervals of 24, 48, 72, 96, 120, or 168h depending on the degree of renal function.ConclusionsRenal impairment was associated with reduced amantadine clearance. Based on pharmacokinetic modeling and simulations, dose regimens were recommended for subjects with impaired renal function to provide systemic amantadine exposure similar to subjects with normal renal function taking a once-daily extended-release amantadine tablet.