Population Pharmacokinetics of Vericiguat in Patients with Heart Failure with Reduced Ejection Fraction: An Integrated Analysis

Vericiguat, a novel stimulator of soluble guanylate cyclase (sGC), is indicated for the treatment of patients following a hospitalization for heart failure or need for outpatient IV diuretics, with symptomatic chronic heart failure and ejection fraction less than 45%. Pharmacokinetic (PK) data from the phase II trial SOCRATES-REDUCED (SOluble guanylate Cyclase stimulatoR in heArT failurE Study) and the phase III trial VICTORIA (Vericiguat Global Study in Patients with Heart Failure with Reduced Ejection Fraction) were used to characterize vericiguat PK. A total of 8,092 concentration records from 2,321 participants (362 from SOCRATES-REDUCED and 1,959 from VICTORIA) were utilized for the development of the population PK (PPK) model. The final PK model was a one-compartment model with first-order absorption and linear elimination. Baseline body weight and time-varying body weight were identified as statistically significant covariates affecting apparent clearance (CL/F) and volume of distribution (V_c ), respectively. Age, sex, race, bilirubin, estimated glomerular filtration rate (eGFR), and albumin did not affect vericiguat PK. Baseline disease-related factors, such as left ventricular ejection fraction, New York Heart Association (NYHA) class, and N-terminal pro B-type natriuretic peptide (NT-proBNP), also did not influence vericiguat PK. Since vericiguat is a titrated drug, the impact of vericiguat PK on the titration to and maintenance of the target dose in VICTORIA was assessed. The distribution of steady-state doses in VICTORIA was similar across CL/F quartiles, suggesting that the ability to reach and maintain dosing at the target 10 mg dose was not related to vericiguat exposure.

Clinical Pharmacology Worldwide: A Global Health Perspective

Low- and middle-income countries (LMICs) have the highest rates of mortality and morbidity globally, but lag behind high-income countries in the number of clinical trials and trained researchers, as well as research data pertaining to their populations. Lack of local clinical pharmacology and pharmacometrics expertise, limited training opportunities, and lack of local genomic data may contribute to health inequalities and limit the application of precision medicine. Continuing to develop health care infrastructure, including well-designed clinical pharmacology training and data collection in LMICs, can help address these challenges. International collaboration aimed at improving training and infrastructure and encouraging locally driven research and clinical trials will be of benefit. This review describes several examples where clinical pharmacology expertise could be leveraged, including opportunities for pharmacogenomic expertise that could drive improved recommendations for clinical guidelines. Also described are clinical pharmacology and pharmacometrics training programs in Africa, and the personal experience of a Tanzanian researcher currently on a training sabbatical in the United States, as illustrative examples of how training in clinical pharmacology can be effectively implemented in LMICs. These training efforts will benefit from advocacy for employment opportunities and career development pathways for clinical pharmacologists that are gradually being recognized and developed in LMICs. Clinical pharmacologists have a key role to play in global health, and development of training and research infrastructure to advance this expertise in LMICs will be of tremendous benefit.

Clinical Pharmacokinetics of the Novel HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitor Doravirine: An Assessment of the Effect of Patient Characteristics and Drug-Drug Interactions

Doravirine (MK-1439) is a novel non-nucleoside reverse transcriptase inhibitor indicated for the combination treatment of human immunodeficiency virus type-1 (HIV-1) infection. The recommended dose is 100 mg once daily. This review summarizes the pharmacokinetics of doravirine, the influence of intrinsic factors, and its drug-drug interaction (DDI) profile. Following oral administration, doravirine is rapidly absorbed (median time to maximum plasma concentration, 1-4 h) and undergoes cytochrome P450 (CYP)3A-mediated oxidative metabolism. Steady-state geometric means for AUC0-24, C24, and Cmax in individuals with HIV-1 following administration of doravirine 100 mg once daily are 37.8 μM·h, 930 nM, and 2260 nM, respectively. Age, gender, severe renal impairment, and moderate hepatic impairment have no clinically meaningful effect on doravirine pharmacokinetics, and there is limited potential for DDIs. No dose adjustment is necessary when doravirine is co-administered with strong CYP3A inhibitors. However, doravirine is contraindicated with strong CYP3A inducers (e.g., rifampin), and dose adjustment of doravirine is recommended for co-administration with the moderate CYP3A inducer, rifabutin. Included in this review are clinical trial data from phase I pharmacokinetic trials, including DDI trials and trials in participants with renal and hepatic disease but without HIV-1 infection (N = 326), as well as phase I, II, and III safety and efficacy trials in participants living with HIV-1 (N = 991). Based on these data, the pharmacokinetic profile of doravirine supports its use in diverse populations living with HIV-1 and allows co-administration with various antiretroviral agents and treatments for commonly occurring co-morbidities.

Physiologically Based Pharmacokinetic Modeling of Doravirine and Its Major Metabolite to Support Dose Adjustment With Rifabutin

Doravirine, a novel nonnucleoside reverse transcriptase inhibitor for the treatment of human immunodeficiency virus 1 (HIV-1), is predominantly cleared by cytochrome P450 (CYP) 3A4 and metabolized to an oxidative metabolite (M9). Coadministration with rifabutin, a moderate CYP3A4 inducer, decreased doravirine exposure. Based on nonparametric superposition modeling, a doravirine dose adjustment from 100 mg once daily to 100 mg twice daily during rifabutin coadministration was proposed. However, M9 exposure may also be impacted by induction, in addition to the dose adjustment. As M9 concentrations have not been quantified in previous clinical studies, a physiologically based pharmacokinetic model was developed to investigate the change in M9 exposure when doravirine is coadministered with CYP3A inducers. Simulations demonstrated that although CYP3A induction increases doravirine clearance by up to 4.4-fold, M9 exposure is increased by only 1.2-fold relative to exposures for doravirine 100 mg once daily in the absence of CYP3A induction. Thus, a 2.4-fold increase in M9 exposure relative to the clinical dose of doravirine is anticipated when doravirine 100 mg twice daily is coadministered with rifabutin. In a subsequent clinical trial, doravirine and M9 exposures, when doravirine 100 mg twice daily was coadministered with rifabutin, were found to be consistent with model predictions using rifampin and efavirenz as representative inducers. These findings support the dose adjustment to doravirine 100 mg twice daily when coadministered with rifabutin.

Exposure-response characterisation of tildrakizumab in chronic plaque psoriasis: Pooled analysis of 3 randomised controlled trials

AIMS

In this exposure-response analysis, the dosing regimen for tildrakizumab, an antibody for treating moderate-to-severe chronic plaque psoriasis, was determined using data from 3 randomised controlled trials (P05495/NCT01225731: phase 2b, n = 355; reSURFACE 1/NCT01722331: phase 3, n = 772; reSURFACE 2/NCT01729754: phase 3, n = 1090).

METHODS

A maximum drug effect (Emax ) logistic-regression exposure-efficacy model was used to describe the week 12 Psoriasis Area and Severity Index (PASI) responses with average concentration of tildrakizumab during weeks 1-12 (Cavg12 ) as exposure metric. The impact of covariates (e.g., body weight, region) was tested. Exposure-safety, longitudinal pharmacokinetic-pharmacodynamic and risk-benefit analyses were also conducted.

RESULTS

At week 12, Emax was estimated at 62.2, 37.9 and 14.6% of responders for PASI75/90/100, respectively. Exposure-response curves plateaued at exposures >5 μg mL-1 . Heavier subjects had a lower response rate to placebo as measured by PASI75/90/100 than lighter subjects. PASI100 placebo response was less in subjects with higher baseline PASI score and older age. Simulated week 12 PASI75 increased by ≤4% on increasing the dose from 100 to 200 mg every 12 weeks (Q12W). The pharmacokinetic-pharmacodynamic model adequately described the time course of PASI change after treatment in the entire population and in each subject. Risk-benefit profiles were favourable for the 100- and 200-mg doses in different weight subgroups.

CONCLUSIONS

Patients with moderate-to-severe psoriasis should receive 100-mg subcutaneous tildrakizumab Q12W. Patients with high body weight (>90 kg) may benefit from a higher dose (200-mg Q12W).

Fine-Needle Aspiration for the Evaluation of Hepatic Pharmacokinetics of Vaniprevir: A Randomized Trial in Patients With Hepatitis C Virus Infection

Fine-needle aspiration (FNA) for serial hepatic sampling may be an efficient and less invasive alternative to core needle biopsy (CNB), the current standard for liver tissue sampling. In this randomized, open-label trial in 31 participants with hepatitis C virus genotype 1 infection (NCT01678131/Merck protocol PN048), we evaluated the feasibility of using FNA to obtain human liver tissue samples appropriate for measuring hepatic pharmacokinetics (PK), using vaniprevir as a tool compound. The primary end point was successful retrieval of liver tissue specimens with measurable vaniprevir concentrations at two of three specified FNA time points. Twenty-nine patients met the primary end point and, therefore, were included in the PK analyses. Hepatic vaniprevir concentrations obtained with FNA were consistent with known vaniprevir PK properties. The shape of liver FNA and CNB concentration-time profiles were comparable. In conclusion, FNA may be effective for serial tissue sampling to assess hepatic drug exposure in patients with liver disease.

Maternal-Neonatal Raltegravir Population Pharmacokinetics Modeling: Implications for Initial Neonatal Dosing

Raltegravir readily crosses the placenta to the fetus with maternal use during pregnancy. After birth, neonatal raltegravir elimination is highly variable and often extremely prolonged, with some neonates demonstrating rising profiles after birth despite removal from the source of extrinsic raltegravir. To establish an appropriate dosing regimen, an integrated maternal–neonatal pharmacokinetics model was built to predict raltegravir plasma concentrations in neonates with in utero raltegravir exposure. Postnatal age and body weight were used as structural covariates. The model predicted rising or decreasing neonatal elimination profiles based on the time of maternal drug administration relative to time of birth and degree of in utero drug disposition into the central and peripheral compartments. Based on this model, it is recommended to delay the first oral dose of raltegravir until 1–2 days of age in those neonates born to mothers who received raltegravir during pregnancy, labor, and delivery.

Population Pharmacokinetic Modeling to Evaluate Standard Magnesium Sulfate Treatments and Alternative Dosing Regimens for Women With Preeclampsia

Magnesium sulfate is the standard therapy for prevention and treatment of eclampsia. Two standard dosing regimens require either continuous intravenous infusion or frequent, large-volume intramuscular injections, which may preclude patients from receiving optimal care. This project sought to identify alternative, potentially more convenient, but similarly effective dosing regimens that could be used in restrictive clinical settings. A 2-compartment population pharmacokinetic (PK) model was developed to characterize serial PK data from 92 pregnant women with preeclampsia who received magnesium sulfate. Body weight and serum creatinine concentration had a significant impact on magnesium PK. The final PK model was used to simulate magnesium concentration profiles for the 2 standard regimens and several simplified alternative dosing regimens. The simulations suggest that intravenous regimens with loading doses of 8 g over 60 minutes followed by 2 g/h for 10 hours and 12 g over 120 minutes followed by 2 g/h for 8 hours (same total dose as the standard intravenous regimen but shorter treatment duration) would result in magnesium concentrations below the toxic range. For the intramuscular regimens, higher maintenance doses given less frequently (4 g intravenously + 10-g intramuscular loading doses with maintenance doses of 8 g every 6 hours or 10 g every 8 hours for 24 hours) or removal of the intravenous loading dose (eg, 10 g intramusculary every 8 hours for 24 hours) may be reasonable alternatives. In addition, individualized dose adjustments based on body weight and serum creatinine were proposed for the standard regimens.

Pharmacokinetics, Safety, and Tolerability of Single-Dose Elbasvir in Participants with Hepatic Impairment

BACKGROUND

The combination of elbasvir and grazoprevir is approved for the treatment of hepatitis C virus genotype 1 or 4 infection.

OBJECTIVE

To evaluate the pharmacokinetics and safety of single-dose elbasvir 50 mg in participants with hepatic impairment.

METHODS

Participants with mild, moderate, or severe hepatic impairment and age-, sex-, and weight-matched healthy controls were enrolled in a 3-part, open-label, sequential-panel, single-dose pharmacokinetic study. Blood samples were collected to assess pharmacokinetics. Safety and tolerability were assessed throughout the study.

RESULTS

Thirty-four participants were enrolled: eight with mild hepatic impairment, 11 with moderate hepatic impairment, seven with severe hepatic impairment, and eight healthy matched controls. Participants with mild, moderate, and severe hepatic impairment demonstrated a numeric, but not statistically significant, decrease in elbasvir exposure compared with controls, with a mean 39, 28, and 12% decrease in area under the concentration-time curve from time 0 extrapolated to infinity, as well as a 42, 31, and 42% decrease in maximum plasma concentration (C _max), respectively. The observed median time to C _max was similar in participants with hepatic impairment and controls. Single-dose administration of elbasvir was well tolerated.

CONCLUSIONS

The pharmacokinetics of elbasvir after a single, oral 50-mg dose were not clinically meaningfully altered in non-HCV-infected participants with mild, moderate, or severe hepatic dysfunction. However, since elbasvir is currently available only as part of a fixed-dose combination with grazoprevir, the fixed-dose combination should not be administered to patients with moderate or severe hepatic impairment, due to the significantly increased plasma grazoprevir exposures in those populations.

Population pharmacokinetic analysis of raltegravir pediatric formulations in HIV-infected children 4 weeks to 18 years of age

P1066 is an open-label study of raltegravir in HIV positive youth, ages 4 weeks-18 years. Here we summarize P1066 pharmacokinetic (PK) data and a population PK model for the pediatric chewable tablet and oral granules. Raltegravir PK parameters were calculated using noncompartmental analysis. A 2-compartment model was developed using data from P1066 and an adult study of the pediatric formulations. Interindividual variability was described by an exponential error model, and residual variability was captured by an additive/proportional error model. Twelve-hour concentrations (C12h ) were calculated from the model-derived elimination rate constant and 8-hour observed concentration. Simulated steady-state concentrations were analyzed by noncompartmental analysis. Target area under the curve (AUC0-12h ) and C12h were achieved in each cohort. For the pediatric formulations, geometric mean AUC0-12h values were 18.0-22.6 μM-hr across cohorts, and C12h values were 71-130 nM, with lower coefficients of variation versus the film-coated tablet. A 2-compartment model with first-order absorption adequately described raltegravir plasma PK in pediatric and adult patients. Weight was a covariate on clearance and central volume and was incorporated using allometric scaling. Raltegravir chewable tablets and oral granules exhibited PK parameters consistent with those from prior adult studies and older children in P1066, as well as lower variability than the film-coated tablet.

Pharmacokinetic-pharmacodynamic studies of the 11β-hydroxysteroid dehydrogenase type 1 inhibitor MK-0916 in healthy subjects

AIMS

To characterize pharmacokinetic parameters of MK-0916 and its safety and tolerability in lean, healthy male subjects following single and multiple oral doses. To assess (by stable-isotope labelling) the in vivo inhibition of cortisone-to-cortisol conversion following oral MK-0916.

METHODS

Data are presented from two randomized, controlled, double-blind, rising-dose phase I studies. In the first study, subjects received single oral doses of 0.4-100 mg MK-0916 (n = 16). In the second study, subjects received 0.2-225 mg MK-0916 followed by daily doses of 0.2-100 mg for 13 days beginning on day 2 or day 15 (n = 80). Plasma and urine drug concentrations were measured for pharmacokinetic analysis. For pharmacodynamic analysis, concentrations of plasma [(13)C4]cortisol were measured by high-pressure liquid chromatography and tandem mass spectrometry following a single oral dose of 5 mg [(13)C4]cortisone.

RESULTS

Doses ≥3 mg were rapidly absorbed (time at which maximal concentration was achieved in plasma, 1.1-1.8 h). Exposure (measured as the area under the concentration-time curve from 0 to 168 h) increased approximately in proportion to dose. Values for the maximal plasma concentration and the plasma concentration at 24 h increased in excess of dose proportionality at doses <6 mg and roughly in proportion to dose at doses >6 mg. In subjects dosed with 6 mg MK-0916 once daily for 14 days, the mean trough plasma concentration was 240 nm and in vivo cortisone-to-cortisol conversion was inhibited by 84%. The relationship between plasma MK-0916 and hepatic 11β-hydroxysteroid dehydrogenase type 1 inhibition was well represented by a simple Emax model with an IC50 of 70.4 nm. Exposure to MK-0916 was generally well tolerated.

CONCLUSIONS

These findings indicate that 11β-hydroxysteroid dehydrogenase type 1 is effectively inhibited in human subjects by doses of MK-0916 that are well tolerated.

The effects of laropiprant on the antiplatelet activity of co-administered clopidogrel and aspirin

Laropiprant is an antagonist of the prostaglandin PGD2 receptor DP1. Laropiprant has a weak affinity for the thromboxane A2 receptor TP. Two double-blinded, randomized, placebo-controlled, crossover studies evaluated the effects of multiple-dose laropiprant at steady state on the antiplatelet effects of multiple-dose aspirin and clopidogrel. Study 1 had two treatment periods, in which each healthy subject received laropiprant 40 mg, clopidogrel 75 mg, and aspirin 80 mg (Treatment A), or placebo, clopidogrel 75 mg, and aspirin 80 mg (Treatment B) once daily for 7 days. Study 2 consisted of three treatment periods. In the first two, each patient with hypercholesterolemia or mixed dyslipidemia received laropiprant 40 mg, clopidogrel 75 mg, and aspirin 81 mg (Treatment A), or placebo, clopidogrel 75 mg, and aspirin 81 mg (Treatment B) once daily for 7 days. In period 3, patients received a single dose of two tablets of extended release nicotinic acid 1 g/laropiprant 20 mg (Treatment C). In both studies, pharmacodynamic endpoints included bleeding time at 24 (primary) and 4 hours (secondary) post-dose following 7 days of once-daily laropiprant in combination with clopidogrel and aspirin, and platelet aggregation in platelet-rich plasma at 4 and 24 hours post-dose on day 7 (secondary). After 7 days, increased bleeding time of 27% (Study 1) and 23% (Study 2) at 24 hours post-dose was observed with laropiprant compared to placebo (both combined with clopidogrel and aspirin), with corresponding upper bounds of the 90% CI marginally exceeding the prespecified upper comparability bound of 1.50 in both studies. The GMR and 90% CI for bleeding time of laropiprant compared to placebo (both combined with clopidogrel and aspirin) at 4 hours post-dose on day 7 was 0.92 (0.70, 1.21) in Study 1, and 1.46 (1.20, 1.78) in Study 2. Compared with placebo, laropiprant (both combined with clopidogrel and aspirin) increased the inhibition of collagen- and ADP-induced platelet aggregation, respectively, by ∼2.4% and ∼8.1% in Study 1 and by ∼4% and ∼5.4% in Study 2, at 24 hours post-dose on day 7. The inhibition of collagen- and ADP-induced platelet aggregation, respectively, was increased by ∼0.1% and ∼5.0% in Study 1, and by ∼5% and ∼12% in Study 2, at 4 hours post-dose on day 7. In conclusion, co-administration of multiple doses of laropiprant with aspirin and clopidogrel induced a prolongation of bleeding time and an inhibitory effect on platelet aggregation ex vivo in healthy subjects and patients with dyslipidemia.

Pharmacokinetics, safety, and 48-week efficacy of oral raltegravir in HIV-1-infected children aged 2 through 18 years

BACKGROUND

IMPAACT P1066 is a phase I/II open-label multicenter trial to evaluate pharmacokinetics, safety, tolerability, and efficacy of multiple raltegravir formulations in human immunodeficiency virus (HIV)-infected youth.

METHODS

Dose selection for each cohort (I: 12 to <19 years; II: 6 to <12 years; and III: 2 to <6 years) was based on review of short-term safety (4 weeks) and intensive pharmacokinetic evaluation. Safety data through weeks 24 and 48, and grade ≥ 3 or serious adverse events (AEs) were assessed. The primary virologic endpoint was achieving HIV RNA <400 copies/mL or ≥ 1 log10 reduction between baseline and week 24.

RESULTS

The targeted pharmacokinetic parameters (AUC0-12h and C12h) were achieved for each cohort, allowing dose selection for 2 formulations. Of 96 final dose subjects, there were 15 subjects with grade 3 or higher clinical AEs (1 subject with drug-related [DR] psychomotor hyperactivity and insomnia); 16 subjects with grade 3 or higher laboratory AEs (1 with DR transaminase elevation); 14 subjects with serious clinical AEs (1 with DR rash); and 1 subjects with serious laboratory AEs (1 with DR transaminase increased). There were no discontinuations due to AEs and no DR deaths. Favorable virologic responses at week 48 were observed in 79.1% of patients, with a mean CD4 increase of 156 cells/µL (4.6%).

CONCLUSIONS

Raltegravir as a film-coated tablet 400 mg twice daily (6 to <19 years, and ≥ 25 kg) and chewable tablet 6 mg/kg (maximum dose 300 mg) twice daily (2 to <12 years) was well tolerated and showed favorable virologic and immunologic responses.

CLINICAL TRIALS REGISTRATION

NCT00485264.

Emerging pharmacology: inhibitors of human immunodeficiency virus integration

The first integrase inhibitor licensed to treat HIV-1 infection was approved in late 2007, more than a decade after the introduction of the first inhibitors of the HIV-1 reverse transcriptase and protease. The unique biochemical and molecular mechanism of action of this novel class of antiretroviral drugs is the fundamental basis for their activity in treating multidrug-resistant HIV-1 infection and is important for understanding both the cellular and in vivo pharmacology and metabolism of these agents. In addition, available pharmacokinetic and drug interaction data for raltegravir and elvitegravir, the two integrase inhibitors that are the most advanced in clinical development to date, are reviewed.

A comparison of the pharmacokinetics of two different formulations of extended-release niacin

OBJECTIVE

The objective of this study was to compare pharmacokinetic parameters of niacin extended-release tablets (NER uncoated) and niacin extended-release caplet formation (NER coated).

RESEARCH DESIGN AND METHODS

Twenty-five healthy male and female subjects were enrolled in a four-period, open-label, randomized, crossover study. Both NER uncoated and NER coated were given as 1 x 1000 mg or 2 x 500 mg tablets. Similarity of NER coated 1 x 1000 mg and NER uncoated 2 x 500 mg was declared if 90% confidence intervals for the geometric mean ratio (GMR) for nicotinuric acid (NUA) Cmax fell within the pre-specified bounds of [0.7, 1.43].

RESULTS

The GMRs for NUA Cmax demonstrated similarity in the pharmacokinetics of NER uncoated 2 x 500 mg, NER coated 1 x 1000 mg, and NER coated 2 x 500 mg. Although less stringent comparability bounds were prespecified for the primary pharmacokinetic endpoint (i.e., Cmax of plasma NUA), inspection of the primary comparison of interest indicated that a hypothesis with more stringent bioequivalence bounds of [0.8, 1.25] would have been satisfied. The NUA Cmax for NER uncoated 1 x 1000 mg was approximately 40% higher than that seen for the other three treatments. In contrast, total urinary excretion of niacin and its metabolites, an approximate measure of bioavailability, was similar for all four treatments.

CONCLUSION

The pharmacokinetic profile of the original NER uncoated formulation dosed as 2 x 500 mg was similar to the new film-coated formulation, NER coated, dosed as 1 x 1000 mg.

Effects of a niacin receptor partial agonist, MK-0354, on plasma free fatty acids, lipids, and cutaneous flushing in humans

BACKGROUND

Development of niacin-like agents that favorably affect lipids with an improved flushing profile would be beneficial.

OBJECTIVE

To evaluate a niacin receptor partial agonist, MK-0354, in Phase I and II studies.

METHODS

The pharmacokinetic/pharmacodynamic effects of single and multiple doses (7 days) of MK-0354 (300-4000 mg) were evaluated in two Phase I studies conducted in healthy men. A Phase II study assessed the effects of MK-0354 2.5 g once daily on lipids during 4 weeks in 66 dyslipidemic patients.

RESULTS

MK-0354 single doses up to 4000 mg and multiple doses (7 days) up to 3600 mg produced robust dose-related reductions in free fatty acid (FFA) over 5 hours. Single doses of MK-0354 300 mg and extended release-niacin (Niaspan) 1 g produced comparable reductions in FFA. Suppression of FFA following 7 daily doses of MK-0354 was similar to that after a single dose. In the Phase II study, MK-0354 2.5 g produced little flushing but no clinically meaningful effects on lipids (placebo-adjusted percent change: high-density lipoprotein cholesterol, 0.4%, 95% confidence interval -5.2 to 6.0; low-density lipoprotein cholesterol, -9.8%, 95% confidence interval -16.8 to -2.7; triglyceride, -5.8%, 95% confidence interval -22.6 to 11.9).

CONCLUSION

Treatment with MK-0354 for 7 days resulted in plasma FFA suppression with minimal cutaneous flushing. However, 4 weeks of treatment with MK-0354 failed to produce changes in high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, or triglycerides.

Absorption, Metabolism, and Excretion of [14C]MK-0524, a Prostaglandin D2 Receptor Antagonist, in Humans

[(3R)-4-(4-Chlorobenzyl)-7-fluoro-5-(methylsulfonyl)-1,2,3,4-tetrahydrocyclopentaindol-3-yl]acetic acid (MK-0524) is a potent orally active human prostaglandin D(2) receptor 1 antagonist that is currently under development for the prevention of niacin-induced flushing. The metabolism and excretion of [(14)C]MK-0524 in humans were investigated in six healthy human volunteers following a single p.o. dose of 40 mg (202 microCi). [(14)C]MK-0524 was absorbed rapidly, with plasma C(max) achieved 1 to 1.5 h postdose. The major route of excretion of radioactivity was via the feces, with 68% of the administered dose recovered in feces. Urinary excretion averaged 22% of the administered dose, for a total excretion recovery of approximately 90%. The majority of the dose was excreted within 96 h following dosing. Parent compound was the primary radioactive component circulating in plasma, comprising 42 to 72% of the total radioactivity in plasma for up to 12 h. The only other radioactive component detected in plasma was M2, the acyl glucuronic acid conjugate of the parent compound. The major radioactive component in urine was M2, representing 64% of the total radioactivity. Minor metabolites included hydroxylated epimers (M1/M4) and their glucuronic acid conjugates, which occurred in the urine as urea adducts, formed presumably during storage of samples. Fecal radioactivity profiles mainly comprised the parent compound, originating from unabsorbed parent and/or hydrolyzed glucuronic acid conjugate of the parent compound. Therefore, in humans, MK-0524 was eliminated primarily via metabolism to the acyl glucuronic acid conjugate, followed by excretion of the conjugate into bile and eventually into feces.

The effect of MK-0524, a prostaglandin D2 receptor antagonist, on prostaglandin D2-induced nasal airway obstruction in healthy volunteers

INTRODUCTION

Nasal congestion in allergic rhinitis results from tissue edema and vasodilatation in the nasal mucosa. Of the mediators released by mast cells in response to allergens, prostaglandin (PG) D(2) is regarded as the most potent inducer of nasal congestion. Intranasal administration of PGD(2) reproduces the nasal blockade experienced by patients with seasonal allergic rhinitis (SAR) via its action on the PGD(2) (DP) receptor to induce nasal vasodilatation. Intranasal challenge with PGD(2) can be a useful tool for evaluating DP-receptor antagonists.

OBJECTIVE

The main purpose of this study was to examine the ability of MK-0524, a DP receptor antagonist in development for the treatment of SAR, to block PGD(2) induced nasal congestion in healthy volunteers.

METHODS

To this end, a double-blind, placebo-controlled, randomized, 3-period study was performed in 15 healthy subjects. During each period, subjects received MK-0524 25 mg, MK-0524 100 mg or placebo qd for 3 days. Twenty-four hours following the last dose, nasal provocations with PGD(2) were performed to determine the PD(75), which is the intranasal dose of PGD(2) that provokes a 75% increase in baseline total nasal airway resistance as performed by active anterior rhinomanometry.

RESULTS

Following treatment with MK-0524, the PD(75) (mean+/-SD) was significantly shifted from 15.8 +/- 18.3 mug/nostril during the placebo period to more than 512 mug/nostril both following the 25- and 100-mg (maximum challenge dose tested) dose regimen.

CONCLUSION

Whether this >45 fold increase in PD(75) will induce a clinically meaningful effect of MK-0524 will require clinical study in participants with SAR.

Antiretroviral Activity, Pharmacokinetics, and Tolerability of MK-0518, a Novel Inhibitor of HIV-1 Integrase, Dosed As Monotherapy for 10 Days in Treatment-Naive HIV-1-Infected Individuals

BACKGROUND

MK-0518 is a novel HIV-1 integrase strand transfer inhibitor with potent in vitro activity against HIV-1 (95% inhibitory concentration [IC95] = 33 nM in 50% human serum) and good bioavailability in uninfected subjects. This study explored the antiretroviral activity and safety of MK-0518 versus placebo for 10 days as monotherapy in antiretroviral therapy-naive HIV-1-infected patients with plasma HIV-1 RNA levels of at least 5000 copies/mL and CD4 T-cell counts of at least 100 cells/mm.

METHODS

This was a multicenter, double-blind, randomized, placebo-controlled 2-part study, with the first part using MK-0518 in 1 of 4 doses (100, 200, 400, and 600 mg) versus placebo (randomized 1:1:1:1:1) given twice daily for 10 days of monotherapy. Patients were monitored for safety, pharmacokinetic parameters, and antiretroviral effect.

RESULTS

Thirty-five patients were enrolled (6-8 patients per treatment group) and completed 10 days of therapy; the mean baseline log10 HIV RNA level ranged from 4.5 to 5.0 copies/mL in each group. On day 10, the mean decrease from baseline in the log10 HIV RNA level was -0.2 copies/mL for the placebo group and -1.9, -2.0, -1.7 and -2.2 log10 copies/mL for the MK-0518 100-, 200-, 400-, and 600-mg treatment groups, respectively. All dose groups had superior antiretroviral activity compared with placebo (P < 0.001 for comparison of each dose with placebo). At least 50% of patients in each MK-0518 dose group achieved an HIV RNA level <400 copies/mL by day 10. Mean trough MK-0518 concentrations at each dose exceeded the IC95 of 33 nM. Study therapy was generally well tolerated. The most common adverse experiences were headache and dizziness; these were similar between active and control groups. There were no discontinuations because of adverse experiences and no serious adverse experiences.

CONCLUSIONS

MK-0518 showed potent antiretroviral activity as short-term monotherapy and was generally well tolerated at all doses. Based on these results, part 2 of the study, a dose-ranging 48-week trial of MK-0518 versus efavirenz in a combination regimen, has been initiated.

Fully automated liquid–liquid extraction for the determination of a novel insulin sensitizer in human plasma by heated nebulizer and turbo ionspray liquid chromatography-tandem mass spectrometry

I, 2-{[5,7-dipropyl-3-(trifluoromethyl)-1,2-benzisoxazol-6-yl]oxy}-2-methyl propionic acid is an alpha peroxisome proliferator-activated receptor (PPAR) agonist with some gamma activity being investigated for potential use in the treatment of Type II diabetes mellitus and dyslipidemia. Two automated liquid-liquid extraction methods were developed and validated for the determination of I in human plasma. Concentrations of I were determined over a wide range of clinical doses. For Method A, plasma was acidified and extracted with ethyl acetate using a fully automated procedure. Analysis was performed by LC-MS/MS with a turbo ionspray source in negative ion mode. For Method B, a larger volume of plasma was extracted and a heated nebulizer source was used on the mass spectrometer. Method A was linear from 0.05 to 50 ng/mL and Method B from 0.2 to 1000 ng/mL. Validation procedures showed that both methods were robust, specific and reproducible.

Simple microscopic theory of Amontons's laws for static friction

A microscopic theory for the ubiquitous phenomenon of static friction is presented. Interactions between two surfaces are modeled by an energy penalty that increases exponentially with the degree of surface overlap. The resulting static friction is proportional to load, in accordance with Amontons's laws. However, the friction coefficient between bare surfaces vanishes as the area of individual contacts grows, except in the rare case of commensurate surfaces. An area independent friction coefficient is obtained for any surface geometry when an adsorbed layer of mobile atoms is introduced between the surfaces. The predictions from our simple analytic model are confirmed by detailed molecular dynamics simulations.