Extended-Duration MK-8591-Eluting Implant as a Candidate for HIV Treatment and Prevention.

Regimen adherence remains a major hurdle to the success of daily oral drug regimens for the treatment and prevention of human immunodeficiency virus (HIV) infection. Long-acting drug formulations requiring less-frequent dosing offer an opportunity to improve adherence and allow for more forgiving options with regard to missed doses. The administration of long-acting formulations in a clinical setting enables health care providers to directly track adherence. MK-8591 (4'-ethynyl-2-fluoro-2'-deoxyadenosine [EFdA]) is an investigational nucleoside reverse transcriptase translocation inhibitor (NRTTI) drug candidate under investigation as part of a regimen for HIV treatment, with potential utility as a single agent for preexposure prophylaxis (PrEP). The active triphosphate of MK-8591 (MK-8591-TP) exhibits protracted intracellular persistence and, together with the potency of MK-8591, supports its consideration for extended-duration dosing. Toward this end, drug-eluting implant devices were designed to provide prolonged MK-8591 release in vitro and in vivo Implants, administered subcutaneously, were studied in rodents and nonhuman primates to establish MK-8591 pharmacokinetics and intracellular levels of MK-8591-TP. These data were evaluated against pharmacokinetic and pharmacodynamic models, as well as data generated in phase 1a (Ph1a) and Ph1b clinical studies with once-weekly oral administration of MK-8591. After a single administration in animals, MK-8591 implants achieved clinically relevant drug exposures and sustained drug release, with plasma levels maintained for greater than 6 months that correspond to efficacious MK-8591-TP levels, resulting in a 1.6-log reduction in viral load. Additional studies of MK-8591 implants for HIV treatment and prevention are warranted.

Exploration of long-acting implant formulations of hepatitis B drug entecavir.

Alternative formulations of entecavir, a once daily oral hepatitis B antiretroviral, may improve treatment adherence by patients. We explored the use of biocompatible polymers to control entecavir dissolution in two formats suitable for subcutaneous implantation. Hot melt extrudates were prepared by extruding entecavir-polymer blends at specified weight ratios. Dip-coated tablets were prepared by compressing entecavir in a multi-tip tooling. Tablets were dip-coated in solutions of polymer and dried. In rodents, entecavir-poly(caprolactone) extrudates demonstrated >180 days of continuous drug release, although below the estimated efficacious target input rate. Drug pharmacokinetic profiles were tunable by varying the polymer employed and implant format. The rank order trends of drug input rates observed in vitro were observed in vivo in the detected plasma concentrations of entecavir. In all dose groups entecavir was not tolerated locally at the site of administration where adverse event severity correlated with drug input rate. These polymer-based implantable formats have applicability to long-acting formulations of high solubility compounds beyond entecavir.