The pharmacokinetics of fenfluramine and norfenfluramine were studied in healthy subjects and in pediatric patients with Dravet syndrome. The steady-state systemic exposure (Cmax and AUC) of fenfluramine was slightly greater than dose proportional over the dose range of 13 to 51.8 mg twice-daily fenfluramine (i.e., 1 to 4 times the maximum recommended dose). In pediatric patients who received FINTEPLA 0.7 mg/kg/day, up to a total daily dose of 26 mg fenfluramine, the geometric mean steady-state fenfluramine (coefficient of variation) Cmax was 68.0 (41%) ng/mL and AUC0-24h was 1390 (44%) ng*h/mL.
Absorption
Fenfluramine has a time to maximum plasma concentration (Tmax) of 4 to 5 hours at steady state. The absolute bioavailability of fenfluramine is approximately 68-74%. There was no effect of food on the pharmacokinetics of fenfluramine or norfenfluramine.
Distribution
The geometric mean (CV%) apparent volume of distribution (Vz/F) of fenfluramine is 11.9 (16.5%) L/kg following oral administration of FINTEPLA in healthy subjects. Fenfluramine is 50% bound to human plasma proteins in vitro and binding is independent of drug concentrations.
Elimination
The elimination half-life of fenfluramine was 20 hours and the geometric mean (CV%) clearance (CL/F) was 24.8 (29%) L/h, following oral administration of FINTEPLA in healthy subjects.
Metabolism
Over 75% of fenfluramine is metabolized to norfenfluramine prior to elimination, primarily by CYP1A2, CYP2B6, and CYP2D6. Other CYP enzymes involved to a minor extent are CYP2C9, CYP2C19, and CYP3A4/5. Norfenfluramine is then deaminated and oxidized to form inactive metabolites.
Excretion
Most of an orally administered dose of fenfluramine (greater than 90%) is excreted in the urine as fenfluramine, norfenfluramine, or other metabolites with fenfluramine and norfenfluramine accounting for less than 25% of the total; less than 5% is found in feces.
Specific Populations
The effect of age (range: 2 to 50 years), sex, and race had no clinically meaningful effect on the pharmacokinetics of fenfluramine.
Drug Interaction Studies
Clinical Studies
Effect of a single dose of stiripentol, clobazam, and valproic acid combination: Coadministration of a single 0.7 mg/kg dose of FINTEPLA, with a single dose of a stiripentol, clobazam, and valproic acid combination in health volunteers, increased the AUC0-INF of fenfluramine by 69% and the Cmax by 18%, and decreased the AUC0-72 hours of norfenfluramine by 41% and the Cmax by 42%, as compared to FINTEPLA administered alone.
Effect of steady state stiripentol plus clobazam, with or without valproate: Fenfluramine pharmacokinetic data were collected from patients after receiving multiple fenfluramine administrations in Study 1 as well as Study 2. Population pharmacokinetic modeling and simulation were used to assess the effect of stiripentol plus clobazam with or without valproate on fenfluramine pharmacokinetics. The effect of stiripentol plus clobazam, with or without valproate, on fenfluramine pharmacokinetics is greater when FINTEPLA is at steady-state than for the first dose of FINTEPLA. When initiating FINTEPLA therapy, coadministration of existing stiripentol plus clobazam with or without valproate is expected to increase the AUC0-24 of the first fenfluramine dose by up to 42% in the patient population. At steady state in the patient population, the coadministration of 0.1 mg/kg twice daily (0.2 mg/kg/day), maximum 17 mg/day, of FINTEPLA with stiripentol plus clobazam with or without valproate, is expected to result in a 166% increase in fenfluramine AUC0-24 and a 38% decrease in norfenfluramine AUC0-24, as compared to 0.2 mg/kg/day, maximum 26 mg/day, FINTEPLA dose administered alone [see Dosage and Administration (2.1, 2.2) and Drug Interactions (7.1)].
Effect of steady state cannabidiol: Coadministration of a single 0.35 mg/kg dose of FINTEPLA with repeated doses of cannabidiol increased the AUC0-INF of fenfluramine by 59% and the Cmax by 10%, and decreased the AUC0-INF of norfenfluramine by 22% and the Cmax by 33%, as compared to FINTEPLA administered alone. This interaction is not expected to be clinically significant.
Effect of FINTEPLA on other drugs: Coadministration of a single 0.7 mg/kg dose of FINTEPLA, with a single dose of a stiripentol, clobazam, and valproic acid combination, did not affect the pharmacokinetics of stiripentol, nor the pharmacokinetics of clobazam or its N-desmethyl-metabolite norclobazam, nor the pharmacokinetics of valproic acid, as compared to the stiripentol, clobazam, and valproic acid combination alone. Coadministration of a single 0.35 mg/kg dose of FINTEPLA, with repeated doses of cannabidiol, did not affect the pharmacokinetics of cannabidiol, as compared to cannabidiol alone.
In Vitro Studies
Fenfluramine is primarily metabolized by CYP1A2, CYP2B6, and CYP2D6 in vitro. Other CYP enzymes involved to a minor extent are CYP2C9, CYP2C19, and CYP3A4/5.
Effect of fenfluramine and norfenfluramine on CYP Substrates: fenfluramine and norfenfluramine are not inhibitors or inducers of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4 at clinically relevant concentrations.
Effect of transporters on fenfluramine and norfenfluramine: fenfluramine and norfenfluramine are not substrates of the P-g, BCRP, OAT1, OAT3, OCT2, MATE1, or MATE2-K transporters.
Effect of FINTEPLA on Transporters: fenfluramine and norfenfluramine are not inhibitors of P-gp, BCRP, OAT1B1, OATP1B3, OAT1, OAT3, OCT2, MATE1, or MATE2-K transporters.