31.7 (± 14.3) mcg•hr/mL and the mean maximal aprepitant concentration (Cmax) was 3.27 (± 1.16) mcg/mL. The mean aprepitant plasma concentration at 24 hours postdose was similar between the 125-mg oral aprepitant dose and the 115-mg intravenous fosaprepitant dose (See Figure 1).
Figure 1: Mean Plasma Concentration of Aprepitant Following 125-mg Oral Aprepitant and 115-mg I.V. Fosaprepitant
Distribution
Fosaprepitant is rapidly converted to aprepitant. Aprepitant is greater than 95% bound to plasma proteins. The mean apparent volume of distribution at steady state (Vdss) is approximately 70 L in humans.
Aprepitant crosses the placenta in rats and rabbits and crosses the blood brain barrier in humans (see CLINICAL PHARMACOLOGY, Mechanism of Action).
Metabolism
Fosaprepitant was rapidly converted to aprepitant in in vitro incubations with liver preparations from nonclinical species (rat and dog) and humans. Furthermore, fosaprepitant underwent rapid and nearly complete conversion to aprepitant in S9 preparations from multiple other human tissues including kidney, lung and ileum. Thus, it appears that the conversion of fosaprepitant to aprepitant can occur in multiple extrahepatic tissues in addition to the liver. In humans, fosaprepitant administered intravenously was rapidly converted to aprepitant within 30 minutes following the end of infusion.
Aprepitant undergoes extensive metabolism. In vitro studies using human liver microsomes indicate that aprepitant is metabolized primarily by CYP3A4 with minor metabolism by CYP1A2 and CYP2C19. Metabolism is largely via oxidation at the morpholine ring and its side chains. No metabolism by CYP2D6, CYP2C9, or CYP2E1 was detected. In healthy young adults, aprepitant accounts for approximately 24% of the radioactivity in plasma over 72 hours following a single oral 300-mg dose of [14C]-aprepitant, indicating a substantial presence of metabolites in the plasma. Seven metabolites of aprepitant, which are only weakly active, have been identified in human plasma.
Excretion
Following administration of a single I.V. 100-mg dose of [14C]-fosaprepitant to healthy subjects, 57% of the radioactivity was recovered in urine and 45% in feces.
Aprepitant is eliminated primarily by metabolism; aprepitant is not renally excreted. The apparent terminal half-life of aprepitant ranged from approximately 9 to 13 hours.
Special Populations
Fosaprepitant, a prodrug of aprepitant, when administered intravenously is rapidly converted to aprepitant.
Gender
Following oral administration of a single 125-mg dose of aprepitant, no difference in AUC0-24hr was observed between males and females. The Cmax for aprepitant is 16% higher in females as compared with males. The half-life of aprepitant is 25% lower in females as compared with males and Tmax occurs at approximately the same time. These differences are not considered clinically meaningful. No dosage adjustment is necessary based on gender.
Geriatric
Following oral administration of a single 125-mg dose of aprepitant on Day 1 and 80 mg once daily on Days 2 through 5, the AUC0-24hr of aprepitant was 21% higher on Day 1 and 36% higher on Day 5 in elderly (≥65 years) relative to younger adults. The Cmax was 10% higher on Day 1 and 24% higher on Day 5 in elderly relative to younger adults. These differences are not considered clinically meaningful. No dosage adjustment is necessary in elderly patients.
Pediatric
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