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 and 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.
Abstract. Peptides are an important class of endogenous ligands that regulate key biological cascades. As such, peptides represent a promising therapeutic class with the potential to alleviate many severe disease states. Despite their therapeutic potential, peptides frequently pose drug delivery challenges to scientists. This review introduces the physicochemical, biophysical, biopharmaceutical, and formulation developability aspects of peptides pertinent to the drug discovery-to-development interface. It introduces the relevance of these properties with respect to the delivery modalities available for peptide pharmaceuticals, with the parenteral route being the most prevalent route of administration. This review also presents characterization strategies for oral delivery of peptides with the aim of illuminating developability issues with the drug candidate. A brief overview of other routes of administration, including inhaled, transdermal, and intranasal routes, is provided as these routes are generally preferred by patients over injectables. Finally, this review presents formulation techniques to mitigate some of the developability obstacles associated with peptide delivery. The authors emphasize opportunities for the thoughtful application of pharmaceutical science to the development of peptide drugs and to the general advancement of this promising class of pharmaceuticals.
Localized drug delivery systems (DDSs) provide therapeutic levels of drug agent while mitigating side effects of systemic delivery. These systems offer controlled release over extended periods of time making them attractive therapies. Monitoring drug dissolution is vital for developing safe and effective means of drug delivery. Currently, dissolution characterization methods are limited to bulk analysis and cannot provide dissolution kinetics at high spatial resolution. However, dissolution rates of drug particles can be heterogeneous with influences from many factors. Insights into finer spatiotemporal dynamics of single particle dissolution could potentially improve pharmacokinetic modeling of dissolution for future drug development. In this work, we demonstrate high-resolution chemical mapping of entecavir, a hepatitis B antiviral drug, embedded in a slow release poly(d,l-lactic acid) formulation with stimulated Raman scattering (SRS) microscopy. By tracking the volume change of individual micron-sized drug particles within the polymer matrix, we establish an analytical protocol for quantitatively profiling dissolution of single crystalline particles in implant formulations in an in situ manner.
The emergence of new active pharmaceutical ingredient (API) polymorphs in pharmaceutical development presents significant risks. Even with thorough polymorph screening, new pathways toward alternate crystal phases can present themselves over the course of formulation development; thus, further improvements in phase screening methods are needed. Herein, a case study is presented of a thermodynamically stable crystalline phase of the HIV drug Islatravir (MK-8591, EFdA) that was not isolated from initial pharmaceutical polymorph screening. In total, five Islatravir phases are identified: one monohydrate and four anhydrate phases. The new phase, anhydrate form IV, was unexpectedly discovered during hot melt extrusion (HME) process development of polymeric implant drug product formulations while probing extreme manufacturing process conditions (elevated shear forces). X-ray diffraction (XRD), differential scanning calorimetry (DSC), and solid-state nuclear magnetic resonance (ssNMR) were utilized as principal tools to identify the new polymorph. The result suggests that HME introduces conditions that may allow a thermodynamically stable crystalline phase to form and these conditions are not necessarily captured by routine pharmaceutical polymorph screening. Subsequent investigations identified procedures to generate the new anhydrate phase without HME equipment by the use of special thermal procedures. It is found that for a crystalline hydrate phase the rate of water loss as well as water entrapment in a heating vessel play a crucial role in phase conversions into different anhydrate polymorphs. Further, the polymer involved in the HME manufacturing process also plays a critical role in the phase conversion, likely by coating the API microparticles and thereby altering the phase conversion kinetics. Strategies presented herein to mimic phase changes during formulation manufacture hold promise for the identification of thermodynamically stable anhydrate forms in earlier stages of pharmaceutical development.
This work develops a mechanistic understanding and a simplified model to understand changes in drug release profiles of an active pharmaceutical ingredient in a long-acting parenteral polymer formulation from changes in its microstructure determined using X-ray computed tomography (XRCT) imaging. The system studied is an implant composed of a solid dispersion of crystalline drug microdomains embedded in a polymer matrix and fabricated by hot melt extrusion. We conduct material characterization of these devises using microCT and introduce, for the first time, imaging of such pharmaceutical devices by means of nanoCT, showing finer structures that cannot be captured by ordinary CT methods. We propose a simplified theoretical mechanistic model that estimates the drug release by extracting relevant microscopic features that modulate the release rate from microCT images to construct an idealized geometry. Using this analysis, we found that although the primary mechanism of resistance was originating from submicrometer features, which are below the resolution of the microCT, the main features that determine changes in diffusivity as a result of different process conditions were microscale pore volume and pore connectivity distributions. The parameters were extracted from the microCT images and in conjunction with the theory were able to explain changes in experimental drug release under different process conditions. These results demonstrate that the modeling strategy can explain the dominant release mechanism and estimate drug release of formulations, even when the equations are simplified due to many assumptions and a lack of subscale information. The proposed approach, due to its simplicity and reliance on the widely employed microCT technique, holds promise for guiding formulation development by providing a rapid initial assessment of batch consistency and process parameter selection before embarking upon lengthy and costly clinical trials.
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