Armodafinil

Absorption

Armodafinil exhibits linear time-independent kinetics following single and multiple oral dose administration. Increase in systemic exposure is proportional over the dose range of 50 to 400 mg. No time-dependent change in kinetics was observed through 12 weeks of dosing. Apparent steady state for armodafinil was reached within 7 days of dosing. At steady state, the systemic exposure for armodafinil is 1.8 times the exposure observed after a single dose. The concentration-time profiles of the R-enantiomer following administration of a single-dose of 50 mg armodafinil or 100 mg modafinil (a 1:1 mixture of R- and S-enantiomers) are nearly superimposable. However, the Cmax and AUC0-∞, of armodafinil at steady-state were approximately 37% and 70% higher, respectively, following administration of 200 mg armodafinil than the corresponding values of modafinil following administration of 200 mg modafinil due to the more rapid clearance of the S-enantiomer (elimination half-life approximately 4 hours) as compared to the R-enantiomer.
Absorption
Armodafinil is readily absorbed after oral administration. The absolute oral bioavailability was not determined due to the aqueous insolubility of armodafinil, which precluded intravenous administration. Peak plasma concentrations are attained at approximately 2 hours in the fasted state. Food effect on the overall bioavailability of armodafinil is considered minimal; however, time to reach peak concentration (tmax) may be delayed by approximately 2 to 4 hours in the fed state. Since the delay in tmax is also associated with elevated plasma concentrations later in time, food can potentially affect the onset and time course of pharmacologic action for armodafinil.
Distribution
Armodafinil has an apparent volume of distribution of approximately 42 L. Data specific to armodafinil protein binding are not available. However, modafinil is moderately bound to plasma protein (approximately 60%), mainly to albumin. The potential for interactions of armodafinil with highly protein-bound drugs is considered to be minimal.
Elimination
After oral administration of armodafinil, armodafinil exhibits an apparent monoexponential decline from the peak plasma concentration. The apparent terminal t½ is approximately 15 hours. The oral clearance of armodafinil is approximately 33 mL/min.
Metabolism
In vitro and in vivo data show that armodafinil undergoes hydrolytic deamidation, S-oxidation, and aromatic ring hydroxylation, with subsequent glucuronide conjugation of the hydroxylated products. Amide hydrolysis is the single most prominent metabolic pathway, with sulfone formation by cytochrome P450 (CYP) 3A4/5 being next in importance. The other oxidative products are formed too slowly in vitro to enable identification of the enzyme(s) responsible. Only two metabolites reach appreciable concentrations in plasma (i.e., R-modafinil acid and modafinil sulfone).
Excretion
Data specific to armodafinil disposition are not available. However, modafinil is mainly eliminated via metabolism, predominantly in the liver, with less than 10% of the parent compound excreted in the urine. A total of 81% of the administered radioactivity was recovered in 11 days post-dose, predominantly in the urine (80% vs. 1.0% in the feces).
Specific Populations
Age
In a clinical study, systemic exposure of armodafinil was approximately 15% higher in elderly subjects (≥65 years of age, N=24), corresponding to approximately 12% lower oral clearance (CL/F), as compared to young subjects (18 to 45 years of age, N=25). Systemic exposure of armodafinil acid (metabolite) was approximately 61% and 73% greater for Cmax and AUC0-τ, respectively, compared to young subjects. Systemic exposure of the sulfone metabolite was approximately 20% lower for elderly subjects compared with young subjects. A subgroup analysis of elderly subjects demonstrated elderly subjects ≥75 and 65 to 74 years of age had approximately 21% and 9% lower oral clearance, respecti …