Safinamide 50 mg · Tablets

The precise mechanism by which XADAGO exerts its therapeutic effects in PD is unknown. XADAGO is an inhibitor of monoamine oxidase B (MAO-B). Inhibition of MAO-B activity, by blocking the catabolism of dopamine, is thought to result in an increase in dopamine levels and a subsequent increase in dopaminergic activity in the brain.

Pharmacokinetics of safinamide is linear over a range of 50 mg to 300 mg (3 times the maximum recommended daily dose). Steady state is reached within 5 to 6 days.

Absorption — After single and multiple oral dosing under fasting conditions, T max of safinamide ranges from 2 to 3 hours. Absolute bioavailability of safinamide is 95% after oral administration, and first pass metabolism is negligible. A slight delay in T max was observed in the fed state relative to the fasted condition, but there was no effect on safinamide AUC 0−∞ and C max [see Dosage and Administration (2.1)] .

Distribution — The volume of distribution (Vss) is approximately 165 L, indicating extensive extravascular distribution. Safinamide is not highly protein bound (unbound fraction is 11 to 12%).

Metabolism and Excretion — In humans, safinamide is almost exclusively eliminated via metabolism (~5% of the drug is eliminated unchanged, mainly in urine), through three main metabolic pathways. One pathway involves hydrolytic oxidation of the amide moiety leading to the primary metabolite 'safinamide acid' (NW-1153). Another pathway is oxidative cleavage of the ether bond forming 'O- debenzylated safinamide' (NW-1199). Finally, the 'N-dealkylated acid' (NW-1689) is formed by oxidative cleavage of the amine bond of either safinamide or the primary safinamide acid metabolite (NW-1153). The 'N-dealkylated acid' (NW-1689) undergoes further conjugation with glucuronic acid yielding its acyl glucuronide. NW-1689 is the main circulating metabolite in human plasma, exceeding the exposure of the parent (161% of parent). NW-1689 AG and NW-1153 account for about 18% and 11% of the parent drug exposure, respectively. None of the metabolites has pharmacological activity.

Safinamide is predominantly metabolized by non-microsomal enzymes (cytosolic amidases/MAO-A); CYP3A4 and other CYP iso-enzymes play only a minor role in its overall biotransformation.

The total clearance of safinamide was determined to be 4.6 L/h. Terminal half-life is 20-26 h. The primary route of excretion is through the kidney (76% of safinamide dose recovered in the urine, primarily in the form of inactive metabolites).