Pharmacokinetics and Pharmacodynamics of Omarigliptin, a Once-Weekly Dipeptidyl Peptidase-4 (DPP-4) Inhibitor, After Single and Multiple Doses in Healthy Subjects.

The pharmacokinetics (PK) and pharmacodynamics (PD) of omarigliptin, a novel once-weekly DPP-4 inhibitor, were assessed following single and multiple doses in healthy subjects. Absorption was rapid, and food did not influence single-dose PK. Accumulation was minimal, and steady state was reached after 2 to 3 weeks. Weekly (area under the curve) AUC and Cmax displayed dose proportionality within the dose range studied at steady state. The average renal clearance of omarigliptin was ∼2 L/h. DPP-4 inhibition ranged from ∼77% to 89% at 168 hours following the last of 3 once-weekly doses over the dose range studied. Omarigliptin resulted in ∼2-fold increases in weighted average postprandial active GLP-1. Omarigliptin acts by stabilizing active GLP-1, which is consistent with its mechanism of action as a DPP-4 inhibitor. Administration of omarigliptin was generally well tolerated in healthy subjects, and both the PK and PD profiles support once-weekly dosing. A model-based assessment of QTc interval risk from the single ascending dose study predicted a low risk of QTc prolongation within the likely clinical dose range, a finding later confirmed in a thorough QT trial.

A semi-mechanistic model for the effects of a novel glucagon receptor antagonist on glucagon and the interaction between glucose, glucagon, and insulin applied to adaptive phase II design.

A potent novel compound (MK-3577) was developed for the treatment of type 2 diabetes mellitus (T2DM) through blocking the glucagon receptor. A semi-mechanistic model was developed to describe the drug effect on glucagon and the interaction between glucagon, insulin, and glucose in healthy subjects (N = 36) during a glucagon challenge study in which glucagon, octreotide (Sandostatin), and basal insulin were infused for 2 h starting from 3, 12, or 24 h postdose of a single 0-900 mg MK-3577 administration. The drug effect was modeled by using an inhibitory E max model (I max = 0.96 and IC50 = 13.9 nM) to reduce the ability of glucagon to increase the glucose production rate (GPROD). In addition, an E max model (E max = 0.79 and EC50 = 575 nM) to increase glucagon secretion by the drug was used to account for the increased glucagon concentrations prechallenge (via compensatory feedback). The model adequately captured the observed profiles of glucagon, glucose, and insulin pre- and postchallenge. The model was then adapted for the T2DM patient population. A linear model to correlate fasting plasma glucose (FPG) to weighted mean glucose (WMG) was developed and provided robust predictions to assist with the dose adjustment for the interim analysis of a phase IIa study.

Quantifying monocyte infiltration in response to intradermal tetanus toxoid injection.

AIMS: To characterize monocyte response in a delayed-type hypersensitivity reaction to intradermal tetanus toxoid (TT) injection. MATERIALS & METHODS: Men with positive serum anti-tetanus titers were stratified by last TT vaccination. Subjects were administered three intradermal injections of TT and one saline control on the same side of the back. Skin biopsies were taken post-injection. After 2 weeks, the procedure was repeated on the contralateral side. RESULTS: Men who received TT booster vaccination 1 month before the study showed greater reproducibility and lower variability in monocyte responses than those who were not revaccinated. Monocyte concentration in subjects re-vaccinated within 1 month of study start appeared maximal at 48 h post-injection. CONCLUSION: This assay represents a novel approach that allows for quantification of dermal monocyte/macrophage influx. This clinical methodology has potential utility in the pharmacodynamic evaluation of therapies targeting inflammatory disorders, which involve monocyte tissue recruitment, like the delayed-type hypersensitivity response.

Pharmacokinetics of lopinavir/ritonavir in HIV/hepatitis C virus-coinfected subjects with hepatic impairment.

The effect of hepatic impairment on lopinavir/ritonavir pharmacokinetics was investigated. Twenty-four HIV-1-infected subjects received lopinavir 400 mg/ritonavir 100 mg twice daily prior to and during the study: 6 each with mild or moderate hepatic impairment (and hepatitis C virus coinfected) and 12 with normal hepatic function. Mild and moderate hepatic impairment showed similar effects on lopinavir pharmacokinetics. When the 2 hepatic impairment groups were combined, lopinavir Cmax and AUC12 were increased 20% to 30% compared to the controls. Hepatic impairment increased unbound lopinavir AUC12 by 68% and Cmax by 56%. The effect of hepatic impairment on low-dose ritonavir pharmacokinetics was more pronounced in the moderate impairment group (181% and 221% increase in AUC12 and Cmax, respectively) than in the mild impairment group (39% and 61% increase in AUC12 and Cmax, respectively). While lopinavir/ritonavir dose reduction is not recommended in subjects with mild or moderate hepatic impairment, caution should be exercised in this population.

Inhibition of murine cytochrome P4501A by tacrine: in vitro studies.

Tacrine, a cholinesterase inhibitor, was approved for the treatment of Alzheimer's disease. Oxidative metabolism of tacrine occurs by CYP1A-catalyzed hydroxylation. In rats, it was observed that the area under the curve (AUC) of the second oral dose was consistently higher than the AUC after the first oral dose, which was not due to the accumulation of the drug in the plasma from the first dose. This finding suggested inhibition of the enzyme during metabolism or inhibition by a metabolite. The inhibitory mechanism was studied in liver and intestinal microsomes prepared from 3-methylcholanthrene-treated rats and with recombinant CYP1A1 and CYP1A2. Preincubation of CYP1A2 with tacrine and NADPH revealed a time-dependent inhibition of 7-ethoxyresorufin O-de-ethylation with a K(i) of 1.94 microM and a k(inact) of 0.091 min(-1). No time-dependent inhibition was observed with CYP1A1 or with 1-hydroxytacrine or 2-hydroxytacrine. Tacrine metabolism catalyzed by CYP1A was also carried out, and the partition ratio was estimated to be 22. A modified Michaelis-Menten equation involving mechanism-based inhibition was derived and used to analyze the data. Reasonable parameter fits were obtained indicating that this equation is suitable to describe metabolism data when the substrate is a mechanism-based inhibitor of the enzyme. The probable inactivation mechanism involves either hydrogen atom abstraction to produce a carbon-centered radical intermediate at the benzylic position or insertion of OH(+) into a C-H bond with subsequent loss of water to produce a carbocation. Rapid rearrangement of the carbocation or radical and subsequent covalent binding of the tacrine moiety would result in enzyme inactivation.