Integrative pharmacokinetic-pharmacodynamic modeling and simulation of amenamevir (ASP2151) for treatment of recurrent genital herpes

Absorption, Distribution, Metabolism, and Excretion of the Novel Helicase-Primase Inhibitor, Amenamevir (ASP2151), in Rodents

BACKGROUND AND OBJECTIVES

The helicase-primase inhibitor amenamevir (ASP2151) is a novel therapeutic agent which has been approved for the treatment of herpes zoster. The present study examined the pharmacokinetic profile of amenamevir in rodents and compared it with data from the literature of past and current established therapies (acyclovir and valaciclovir) to provide additional data to facilitate drug discovery and proper drug use.

METHODS

In situ absorption, blood and plasma radioactivity concentrations, tissue distribution, and excretion were determined using liquid scintillation counting. Plasma amenamevir concentrations were measured using a validated chromatographic method. Chemical structures of in vivo metabolites were investigated using liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy.

RESULTS

Amenamevir, after single intravenous administration to mice, had an elimination half-life of 2 h. Bioavailability was 40% after single oral administration. In situ absorption data indicated that amenamevir is mainly absorbed in the small intestine. The main component in mouse plasma was amenamevir, accounting for 87.9% of amenamevir-derived components. Our results suggest that the main elimination pathway in mice is oxidative metabolism at a methyl group and a 1,2,3-trisubstituted benzene ring followed by biliary and fecal excretion. Following oral administration of ¹⁴C-amenamevir to mice, 100.63% of the dose (10.06% in urine and 90.46% in feces) was excreted by 96 h post-dose.

CONCLUSIONS

The underlying mechanism of the improved pharmacokinetic profile of amenamevir was linked to an improved absorption ratio (not hepatic availability) compared to acyclovir, and qualitative differences in elimination (slow metabolism of amenamevir vs rapid urinary excretion of acyclovir/valaciclovir).

An Open-Label, Single-Dose, Human Mass Balance Study of Amenamevir in Healthy Male Adults

Amenamevir is an inhibitor of the helicase-primase enzyme complex developed for the treatment of varicella zoster virus. This mass balance study investigated the absorption, metabolism, and excretion of a single dose (200 mg) of ¹⁴ C-labeled amenamevir in healthy male volunteers. Blood, urine, and feces samples were collected for up to 8 days after the dose. Safety and tolerability were assessed through voluntary reporting of adverse events, physical examination, and clinical laboratory testing. Amenamevir was rapidly absorbed, with a median time to peak drug concentration of 1.0 to 1.5 hours and a plasma half-life of 8 to 9 hours. Overall, 95.3% of the administered dose was recovered, with the majority of radiolabeled drug excreted in feces (74.6%) followed by urine (20.6%). The major route of elimination was fecal, with around 70% of the dose excreted as metabolites and <0.1% as the unchanged drug. Metabolic profiling revealed that predominantly radiolabeled amenamevir (80%) and its hydroxyl metabolite R5 (up to 7.1%) were present in plasma. Single-dose amenamevir was well tolerated; 3 transient and mild adverse events were reported in 3 subjects. Overall, >95% of a single 200-mg dose of amenamevir was eliminated by 168 hours after the dose, with the major route of elimination being fecal.