GOCOVRI is an extended-release formulation. The pharmacokinetics of amantadine from 68.5 mg, 137 mg, and 274 mg of GOCOVRI are dose proportional in healthy subjects.
Absorption
After a single dose bedtime administration of GOCOVRI, the median T
maxfor plasma amantadine was around 12 hours (range 6-20 hours). The steady-state concentrations of GOCOVRI were achieved 4 days after the dose initiation. The steady-state total exposures (AUC
0-tau) were 20-30% higher than after single dose, suggesting an accumulation ratio of 1.2-1.3.
Effect of Food
A single dose crossover study of GOCOVRI established the lack of effect of high-fat, high-calorie meal on plasma amantadine pharmacokinetics; additionally, administration of entire capsule contents sprinkled on applesauce also did not affect plasma amantadine pharmacokinetics.
Distribution
The volume of distribution determined after the intravenous administration of amantadine to 15 healthy subjects was 3 to 8 L/kg, suggesting potential extravascular distribution. Amantadine is approximately 67% bound to plasma proteins over a concentration range of 0.1 to 2.0 µg/mL.
Elimination
In a study with healthy volunteers after oral administration, the apparent plasma clearance of amantadine was estimated to be 0.27 ± 0.094 L/hr/kg (range 0.13 to 0.57 L/hr/kg). Amantadine is primarily excreted unchanged in the urine, and in a study of six healthy volunteers, the ratio of amantadine renal clearance to apparent plasma clearance was 0.79 ± 0.17 (mean ± SD). The mean plasma amantadine half-life at steady-state was approximately 16 hours.
Metabolism
Eight metabolites of amantadine have been identified in human urine. One metabolite, an N-acetylated compound, was quantified in human urine and accounted for 0-15% of the administered dose in multiple studies. The contribution of this metabolite to efficacy or toxicity is not known.
Excretion
Amantadine is primarily excreted unchanged in the urine by both glomerular filtration and tubular secretion.
Specific Population
Male/Female Patients
In an integrated analysis of five studies in healthy volunteers (n=147), the mean total amantadine clearance following administration of GOCOVRI, adjusted for body weight in kilograms, was 1.2 fold higher in males compared to females (95% CI: 1.1, 1.3, P=0.007). No dose adjustment by gender is warranted.
Renal Impairment
The renal clearance of amantadine is significantly lower in adult patients with moderate or severe renal impairment, compared to healthy adults. Since the renal pathway is a major elimination pathway, impairment in renal function can result in significant accumulation in the plasma, warranting dose adjustment. The impact of renal impairment on dose adjustment was not investigated in a dedicated study.
Based on PK simulations, the range of the total exposures (AUC
0-tau) in subjects with normal renal function (creatinine clearance >90 mL/min/1.73 m
2) or mild renal impairment (creatinine clearance between 60 and 89 mL/min/1.73 m
2) were comparable for the same dosing regimen. However, patients with moderate renal impairment (creatinine clearance between 30 and 59 mL/min/1.73 m
2) had higher exposures relative to patients with normal renal function or mild renal impairment. Severe renal impairment (creatinine clearance between 15 and 29 mL/min/1.73 m
2) resulted in even higher total exposures. Dosage adjustment is recommended in patients with moderate and severe renal impairment
[see Use in Special Populations (
8.6) and Dosage and Administration (
2.3)].
GOCOVRI is contraindicated in patients with end stage renal disease (creatinine clearance less than 15 mL/min/1.73 m
2).
Amantadine is inefficiently removed by hemodialysis.
Drug Interaction Studies
The in-vitro dissolution-release profiles showed 52% drug release after 45 minutes, and up to 95% after 2 hours, at concentrations of 40% alcohol/0.1N HCl.
In vitro studies indicate that amantadine has negligible or no inhibitory activity against cellular transporters (P-gp, BCRP, MATE2-K, OAT1, OAT3, OATP1B1, and OATP1B3) at plasma concentrations observed in patients with Parkinson's disease on a GOCOVRI 274 mg dose.
In vitro studies in MDCK-II cells demonstrated that amantadine is not a substrate of the anionic transporters OAT1 or OAT3, or the cationic transporter MATE2-K. Amantadine was a poor substrate of the cationic transporters OCT2 and MATE1. Renal elimination of amantadine may be mediated in part by one or more organic cation transporters independent of OCT2. An in vivo study demonstrated that quinidine, a known organic cation transporter inhibitor, reduced amantadine clearance by approximately 33% in humans. The clinical significance is unknown. In vitro studies show that amantadine does not significantly inhibit the enzyme activity of drug metabolizing cytochrome P450 isoforms (CYP1A2, 2B6, 2C19, 2C8, 2C9, 2D6, 2E1, 3A4, and 3A5).