Publications by authors named "Samantha Abel"

20 Publications

  • Page 1 of 1

Identification of Racial Inequities in Access to Specialized Inpatient Heart Failure Care at an Academic Medical Center.

Circ Heart Fail 2019 11 29;12(11):e006214. Epub 2019 Oct 29.

Division of Cardiovascular Medicine, and Department of Medicine (E.F..L.), Brigham and Women's Hospital, Boston, MA.

Background: Racial inequities for patients with heart failure (HF) have been widely documented. HF patients who receive cardiology care during a hospital admission have better outcomes. It is unknown whether there are differences in admission to a cardiology or general medicine service by race. This study examined the relationship between race and admission service, and its effect on 30-day readmission and mortality Methods: We performed a retrospective cohort study from September 2008 to November 2017 at a single large urban academic referral center of all patients self-referred to the emergency department and admitted to either the cardiology or general medicine service with a principal diagnosis of HF, who self-identified as white, black, or Latinx. We used multivariable generalized estimating equation models to assess the relationship between race and admission to the cardiology service. We used Cox regression to assess the association between race, admission service, and 30-day readmission and mortality.

Results: Among 1967 unique patients (66.7% white, 23.6% black, and 9.7% Latinx), black and Latinx patients had lower rates of admission to the cardiology service than white patients (adjusted rate ratio, 0.91; 95% CI, 0.84-0.98, for black; adjusted rate ratio, 0.83; 95% CI, 0.72-0.97 for Latinx). Female sex and age >75 years were also independently associated with lower rates of admission to the cardiology service. Admission to the cardiology service was independently associated with decreased readmission within 30 days, independent of race.

Conclusions: Black and Latinx patients were less likely to be admitted to cardiology for HF care. This inequity may, in part, drive racial inequities in HF outcomes.
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http://dx.doi.org/10.1161/CIRCHEARTFAILURE.119.006214DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7183732PMC
November 2019

Pediatric laparoscopic appendectomy, risk factors, and costs associated with nationwide readmissions.

J Surg Res 2017 07 20;215:245-249. Epub 2017 Apr 20.

Division of Pediatric Surgery, DeWitt-Daughtry Family Department of Surgery, Leonard M. Miller School of Medicine, University of Miami, Miami, Florida. Electronic address:

Background: Previous studies of readmission after pediatric laparoscopic appendectomy have been limited to individual hospitals or noncompeting public pediatric hospitals. The purpose of this study was to evaluate the risk factors and costs associated with nonelective, 30-d readmissions in pediatric patients nationwide across public and private hospitals.

Materials And Methods: The Nationwide Readmission Database for 2013 was queried for all patients under the age of 18 y with a diagnosis of acute appendicitis undergoing laparoscopic appendectomy. Using multivariate logistic regression with 26 different variables, the odds ratios (ORs) for nonelective readmissions within 30 d were determined. The costs of readmission were calculated as well as the most common diagnoses on readmission.

Results: In 2013, there were 12,730 patients under the age of 18 y undergoing laparoscopic appendectomy, and 3.4% were readmitted within 30 d. The overall mean age was 11.6 ± 3.8 y, and the mean age of the readmitted patients was 10.7 ± 4.0 whereas the mean age of patients not readmitted was 11.6 ± 3.8 (P < 0.01, 95% CI: 0.54-1.26). The total cost of readmissions was $3,645,502 with a weighted nationwide estimated cost of $10,351,690. The mean readmission cost was $8304 ± 7864. The most common diagnosis group on readmission was postoperative, posttraumatic, other device infections (36.0%), whereas the most common principal diagnosis was other postoperative infection (38.5%) and the most common secondary diagnosis was peritoneal abscess (11.9%).

Conclusions: Readmission within 30 d after laparoscopic appendectomy in pediatric patients represents a significant resource burden. This study elucidates the patient characteristics that predispose these patients to readmission. Efforts to reduce these readmissions should be focused around preventing infections in patients with these predisposing risk factors.
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http://dx.doi.org/10.1016/j.jss.2017.04.005DOI Listing
July 2017

Novel Causative Variants in , and Associated with Intellectual Disability and Additional Phenotypic Features.

J Pediatr Genet 2017 Jun 14;6(2):77-83. Epub 2017 Feb 14.

Dr. John T. Macdonald Foundation Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami, Miller School of Medicine, Miami, Florida, United States.

Patients with unclear patterns of developmental and cognitive delay may go years without a definitive diagnosis despite extensive testing due to overlapping phenotypes of many genetic disorders. In this study, we identified causative variants in , , or in four individuals with global developmental delay and various findings including microcephaly and sensorineural hearing loss using whole exome sequencing. We present the cognitive, neurologic, and physical findings of four individuals to expand the clinical knowledge of possible features of the phenotypes of three rare genetic disorders. Through this process, we provide support for the use of whole exome sequencing in the setting of severe, intellectual disability or in those in whom a genetic disorder is suspected despite initial negative testing.
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http://dx.doi.org/10.1055/s-0037-1598639DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5423827PMC
June 2017

Imaging through the pupal case of Drosophila melanogaster.

J Vis Exp 2014 Jan 23(83):e51239. Epub 2014 Jan 23.

Department of Biology, University of Miami.

The longstanding use of Drosophila as a model for cell and developmental biology has yielded an array of tools. Together, these techniques have enabled analysis of cell and developmental biology from a variety of methodological angles. Live imaging is an emerging method for observing dynamic cell processes, such as cell division or cell motility. Having isolated mutations in uncharacterized putative cell cycle proteins it became essential to observe mitosis in situ using live imaging. Most live imaging studies in Drosophila have focused on the embryonic stages that are accessible to manipulation and observation because of their small size and optical clarity. However, in these stages the cell cycle is unusual in that it lacks one or both of the gap phases. By contrast, cells of the pupal wing of Drosophila have a typical cell cycle and undergo a period of rapid mitosis spanning about 20 hr of pupal development. It is easy to identify and isolate pupae of the appropriate stage to catch mitosis in situ. Mounting intact pupae provided the best combination of tractability and durability during imaging, allowing experiments to run for several hours with minimal impact on cell and animal viability. The method allows observation of features as small as, or smaller than, fly chromosomes. Adjustment of microscope settings and the details of mounting, allowed extension of the preparation to visualize membrane dynamics of adjacent cells and fluorescently labeled proteins such as tubulin. This method works for all tested fluorescent proteins and can capture submicron scale features over a variety of time scales. While limited to the outer 20 µm of the pupa with a conventional confocal microscope, this approach to observing protein and cellular dynamics in pupal tissues in vivo may be generally useful in the study of cell and developmental biology in these tissues.
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http://dx.doi.org/10.3791/51239DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4089621PMC
January 2014

Pharmacokinetic interactions of maraviroc with darunavir-ritonavir, etravirine, and etravirine-darunavir-ritonavir in healthy volunteers: results of two drug interaction trials.

Antimicrob Agents Chemother 2011 May 7;55(5):2290-6. Epub 2011 Mar 7.

Tibotec, Inc., 1125 Trenton-Harbourton Rd., K20605, Titusville, NJ 08560, USA.

The effects of darunavir-ritonavir at 600 and 100 mg twice daily (b.i.d.) alone, 200 mg of etravirine b.i.d. alone, or 600 and 100 mg of darunavir-ritonavir b.i.d. with 200 mg etravirine b.i.d. at steady state on the steady-state pharmacokinetics of maraviroc, and vice versa, in healthy volunteers were investigated in two phase I, randomized, two-period crossover studies. Safety and tolerability were also assessed. Coadministration of 150 mg maraviroc b.i.d. with darunavir-ritonavir increased the area under the plasma concentration-time curve from 0 to 12 h (AUC12) for maraviroc 4.05-fold relative to 150 mg of maraviroc b.i.d. alone. Coadministration of 300 mg maraviroc b.i.d. with etravirine decreased the maraviroc AUC12 by 53% relative to 300 mg maraviroc b.i.d. alone. Coadministration of 150 mg maraviroc b.i.d. with etravirine-darunavir-ritonavir increased the maraviroc AUC12 3.10-fold relative to 150 mg maraviroc b.i.d. alone. Maraviroc did not significantly affect the pharmacokinetics of etravirine, darunavir, or ritonavir. Short-term coadministration of maraviroc with darunavir-ritonavir, etravirine, or both was generally well tolerated, with no safety issues reported in either trial. Maraviroc can be coadministered with darunavir-ritonavir, etravirine, or etravirine-darunavir-ritonavir. Maraviroc should be dosed at 600 mg b.i.d. with etravirine in the absence of a potent inhibitor of cytochrome P450 3A (CYP3A) (i.e., a boosted protease inhibitor) or at 150 mg b.i.d. when coadministered with darunavir-ritonavir with or without etravirine.
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http://dx.doi.org/10.1128/AAC.01046-10DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3088221PMC
May 2011

Pharmacokinetic interaction of ritonavir-boosted elvitegravir and maraviroc.

J Acquir Immune Defic Syndr 2010 Feb;53(2):209-14

Gilead Sciences, Inc, Foster City, CA 94404, USA.

Background: The pharmacokinetic (PK) interaction between ritonavir-boosted elvitegravir (elvitegravir/r) and maraviroc was evaluated.

Methods: Healthy subjects were randomized to receive elvitegravir/r (150/100 mg once daily) before or after elvitegravir/r plus maraviroc (150 mg twice daily) (group 1; n = 20) or receive maraviroc before or after maraviroc plus elvitegravir/r (group 2; n = 16). All regimens were administered for 10 days and elvitegravir, ritonavir, and maraviroc PK determined. Lack of PK alteration was defined as 90% confidence intervals for ratio of geometric least squares means ratio (coadministration:alone) between 70% and 143% for elvitegravir and ritonavir Cmax (maximum concentration), Ctau (trough), and AUCtau (area under plasma concentration-time curve; 0-24 hours); for maraviroc, given a 100% increase in Cmax and AUCtau (0-12 hours); the predicted 90% confidence intervals were 162% to 247% and 136% to 295%, respectively.

Results: Twenty-eight of 36 enrolled subjects completed the study; one discontinuation was due to an adverse event. The most common adverse event across treatments was headache. Upon coadministration, elvitegravir and ritonavir PK were unaltered, but maraviroc exposures were 2-fold to 4-fold higher presumably due to ritonavir-mediated CYP3A-/Pgp inhibition.

Conclusions: During elvitegravir/r plus maraviroc administration, no elvitegravir or ritonavir dose change and a reduced 150-mg dose of maraviroc are recommended.
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http://dx.doi.org/10.1097/QAI.0b013e3181ba4536DOI Listing
February 2010

Pharmacokinetics, safety and tolerability of a single oral dose of maraviroc in HIV-negative subjects with mild and moderate hepatic impairment.

Antivir Ther 2009 ;14(6):831-7

Pfizer Global Research and Development, Sandwich, UK.

Background: Maraviroc is the first CCR5 antagonist and only oral entry inhibitor approved for the treatment of HIV type-1 infection. Maraviroc is extensively metabolized, primarily by cytochrome P450 3A4 and hence its pharmacokinetics might be affected by impaired hepatic function. The objective of this study was to evaluate the pharmacokinetics of maraviroc in subjects with mild or moderate hepatic impairment compared with subjects with normal hepatic function. Safety and tolerability were also assessed.

Methods: This was an open-label, non-randomized, single-centre, parallel-group study. A total of 24 subjects with mild (n=8) or moderate (n=8) hepatic impairment, or normal hepatic function (n=8) received a single dose of 300 mg maraviroc.

Results: Relative to those with normal hepatic function, the geometric mean ratio (90% confidence interval) for the maximum observed plasma concentration (C(max)) of maraviroc was 111% (74.6-166) and 132% (89.6-194) for those with mild and moderate hepatic impairment, respectively; the area under the concentration-time curve from time 0 to the last quantifiable concentration (AUC(last)) was 125% (84.7-185) and 146% (100-212); oral clearance was 89% (53.2-150) and 83% (49.2-139); and renal clearance was 94% (70.5-126) and 131% (98.6-173), respectively. Maraviroc was well tolerated in all subjects.

Conclusions: Although differences in maraviroc pharmacokinetics were noted in subjects with hepatic impairment compared with those with normal hepatic function, these do not currently support a dose modification. The single 300 mg dose of maraviroc was well tolerated by subjects with normal and impaired hepatic function.
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http://dx.doi.org/10.3851/IMP1297DOI Listing
December 2009

Maraviroc: pharmacokinetics and drug interactions.

Antivir Ther 2009 ;14(5):607-18

Pfizer Global Research and Development, Sandwich, UK.

Maraviroc is a potent selective CCR5 antagonist and is the first of this new class of oral agents to be approved for the treatment of CCR5-tropic HIV type-1. Maraviroc is extensively metabolized by CYP3A4, with renal clearance accounting for approximately 23% of total clearance. The half-life of maraviroc is approximately 16 h. Maraviroc does not inhibit any of the major CYP450 enzymes at clinically relevant doses and it has not shown any clinically relevant effects on plasma concentrations of other agents; hence, no dose adjustments of coadministered agents are required. Maraviroc exposure is altered by agents that modulate the activity of CYP3A4 and, in some circumstances, maraviroc dose adjustment is necessary. This article aims to review all pharmacokinetic and drug interaction data available for maraviroc, and to provide a comprehensive summary of the dose adjustment recommendations for maraviroc when coadministered with agents from all classes of antiretroviral therapy as well as other commonly coadministered agents.
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September 2009

Pharmacokinetics, safety and tolerance of voriconazole in renally impaired subjects: two prospective, multicentre, open-label, parallel-group volunteer studies.

Clin Drug Investig 2008 ;28(7):409-20

Pfizer Global Research and Development, Sandwich, UK.

Background And Objectives: Since little is known regarding the pharmacokinetics of voriconazole in renally impaired patients, two prospective, open-label, parallel-group volunteer studies were conducted to estimate the effect of renal impairment on the pharmacokinetics of oral voriconazole and intravenous voriconazole solubilized with sulphobutylether-beta-cyclodextrin (SBECD), respectively.

Methods: In study A, male subjects with no (n = 6), mild (n = 6), moderate (n = 6) or severe (n = 6) renal impairment received one 200 mg dose of oral voriconazole. Voriconazole plasma levels were periodically assessed until 48 hours post-dose. In study B, male subjects with no (n = 6) or moderate (n = 7) renal impairment received multiple doses of intravenous voriconazole solubilized with SBECD (6 mg/kg twice daily [day 1] then 3 mg/kg twice daily [days 2-6] followed by a final dose of 3 mg/kg on the morning of day 7) at an infusion rate of 3 mg/kg/h. Voriconazole plasma levels were periodically assessed until 36 hours following the final dose. Pharmacokinetics were determined by non-compartmental methods.

Results: The pharmacokinetics of voriconazole were unaffected in subjects with any degree of renal impairment in both studies. In study B, clearance of SBECD was proportional to creatinine clearance (r2 = 0.857). Although two subjects had >30% increase in serum creatinine from baseline, these changes did not correlate with SBECD trough levels (r2 = 0.053). The majority of subjects with moderate renal insufficiency were able to tolerate 7 days of intravenous voriconazole solubilized with SBECD.

Conclusion: These data suggest that renal impairment does not affect the pharmacokinetics of voriconazole. Furthermore, in subjects with moderate renal impairment, there is a strong linear correlation between SBECD clearance and creatinine clearance, and elevated SBECD levels do not necessarily correlate with increased serum creatinine levels (an indicator of worsening renal function).
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http://dx.doi.org/10.2165/00044011-200828070-00002DOI Listing
November 2008

Population pharmacokinetic/pharmacodynamic analysis of CCR5 receptor occupancy by maraviroc in healthy subjects and HIV-positive patients.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:86-94

Department of Clinical Pharmacology, Pfizer Global R&D, Groton, CT, USA.

Background: Maraviroc, a noncompetitive antagonist of the CCR5 coreceptor, was recently approved in the USA as a treatment of HIV infection. For antiretroviral agents that target the virus, antiviral effect can be related to some extent to plasma drug concentrations. For CCR5 antagonists that target the host cells, receptor occupancy in vivo might be a better predictor of efficacy. AIMS To develop a population pharmacokinetic (PK)-pharmacodynamic (PD) model that describes CCR5 receptor occupancy by maraviroc after oral administration at different doses in healthy volunteers and HIV-positive patients and to assess the relevance of receptor occupancy in predicting the decrease in viral load (HIV-1 RNA copies ml(-1)) in HIV-positive patients.

Methods: Receptor occupancy data from 88 individuals enrolled in two multiple dose trials were included in the population PK-receptor binding model. Out of the 88 individuals, 25 were HIV-1-infected patients and had viral load measurements, whereas the remaining 63 were healthy volunteers. Doses ranged from 3 mg b.i.d. to 600 mg q.d. A previously published PK-PD disease model describing the effect of maraviroc on the viral load was updated by replacing its PD module by the receptor occupancy model. Simulated viral load-time profiles with the updated model were compared with the profiles observed in patients.

Results: The majority of measured plasma concentrations were associated with receptor occupancy > or = 50% even at the lowest dose of 3 mg b.i.d. A simple direct E(max) model appeared to describe satisfactorily the PK-receptor occupancy relationship. The estimated K(D) was around 0.0894 ng ml(-1), far below the operational in vivo antiviral IC(50) of 8 ng ml(-1). Accordingly, simulations led to marked overprediction of the decrease in viral load-time profiles.

Conclusions: Maraviroc receptor occupancy close to the maximum is required to induce a significant decrease in viral load, indicating that in vivo CCR5 receptor occupancy by maraviroc is not a direct measure of drug inhibitory activity. Considering the imprecision of the measurement in the upper flat part of the maraviroc concentration vs. percent CCR5 occupancy curve, it can reasonably be concluded that routine monitoring of receptor occupancy as a biomarker for maraviroc efficacy will not be helpful. Based on this analysis, it was decided not to use receptor occupancy as a biomarker of viral load inhibition during the development of CCR5 antagonist compounds.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03140.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311409PMC
April 2008

Assessment of the absorption, metabolism and absolute bioavailability of maraviroc in healthy male subjects.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:60-7

Pfizer Global R&D, Sandwich, UK.

Aims: Two studies were conducted to: (i) quantify the amount of drug-related radioactivity in blood, plasma, urine and faeces following a (14)C-labelled dose of maraviroc; and (ii) investigate the pharmacokinetics, safety and tolerability of intravenous (i.v.) maraviroc and determine the absolute bioavailability of oral maraviroc. Metabolite profiling was also conducted. Data from both of these studies were used to construct a mass-balance model for maraviroc.

Methods: Study 1 was an open-label study in three healthy male subjects. All subjects received a single 300-mg oral solution dose of (14)C-labelled maraviroc. Study 2 included two cohorts of subjects. Cohort 1 involved a double-blind (third party open), four-way crossover study where eight subjects received escalating i.v. doses of maraviroc (3, 10 and 30 mg) with placebo insertion. Cohort 2 involved an open, two-way crossover study where 12 subjects received 30 mg maraviroc by i.v. infusion and 100 mg maraviroc orally in random order. In study 1, blood samples and all urine and faeces were collected up to at least 120 h postdose. In study 2, blood samples were taken at intervals up to 48 h postdose. Urine was also collected up to 24 h postdose in cohort 1 only.

Results: After oral administration in study 1, maraviroc was rapidly absorbed with a plasma T(max) reached by 2 h postdose for all three subjects. The maximum concentrations of radioactivity also occurred within 2 h for all subjects. There was a higher amount of radioactivity in plasma than in blood (blood/plasma ratio approximately 0.6 for AUC(t) and C(max)). Unchanged maraviroc was the major circulating component in plasma, accounting for approximately 42% of the circulating radioactivity. Following a 300-mg (14)C-labelled maraviroc dose, means of 76.4% and 19.6% of radioactivity were recovered in the faeces and urine, respectively. The mean total recovery of dosed radioactivity was 96%, with the majority of radioactivity being recovered within 96 h postdose. Profiling of the urine and faeces showed similar and extensive metabolism in all subjects. Unchanged maraviroc was the major excreted component (33%). The major metabolic pathways were determined and involved oxidation and N-dealkylation. Intravenous doses of maraviroc (3-30 mg) were well tolerated in study 2, and drug exposure was approximately proportional to dose within the studied range. Approximately 23% of total clearance (44 l h(-1)) was accounted for by renal clearance (10.2 l h(-1)). Mean volume of distribution at steady state was 194 l. Absolute bioavailability of a 100-mg oral tablet dose, by comparison with a 30-mg i.v. dose, was calculated to be 23.1%.

Conclusions: Maraviroc is rapidly absorbed and extensively metabolized, although unchanged maraviroc is the major circulating component in plasma and is the major excreted component after oral dosing. The pharmacokinetics of maraviroc after i.v. administration is approximately proportional over the dose range studied. Renal clearance contributes 23% of total clearance. The absolute bioavailability of 100 mg oral maraviroc is 23%.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03137.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311408PMC
April 2008

The effects of cotrimoxazole or tenofovir co-administration on the pharmacokinetics of maraviroc in healthy volunteers.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:47-53

Pfizer Global R&D, Sandwich, UK.

Aims: To assess the potential of cotrimoxazole and tenofovir, drugs which are inhibitors and/or substrates of renal transporters, to alter the pharmacokinetic profile of maraviroc.

Methods: Two randomized, placebo-controlled, two-way crossover studies were conducted in healthy male and female subjects. In study 1, 16 subjects, aged 18-45 years, received maraviroc (300 mg b.i.d.) with and without cotrimoxazole (960 mg b.i.d.; 160 mg trimethoprim and 800 mg sulfamethoxazole). In study 2, 12 subjects, aged 21-45 years, received maraviroc (300 mg b.i.d.) with and without tenofovir (300 mg q.d.). For study 1, blood was collected predose and on days 1-7. In study 2, blood was collected predose, on day 1 and days 3-7. In both studies, blood was collected at intervals up to 12 h postdose on day 7. Urine was collected on day 7, 0-12 h post morning dose. Blood and urine were analysed for maraviroc using liquid chromatography/tandem mass spectrometry.

Results: The geometric mean ratios for C(max) and AUC(12) were 119% and 111%, respectively, for maraviroc plus cotrimoxazole and 104% and 103%, respectively, for maraviroc plus tenofovir, compared with maraviroc plus placebo. Renal clearance of maraviroc plus placebo was 8.3 l h(-1) and 8.5 l h(-1) and was 7.8 l h(-1) for maraviroc plus cotrimoxazole and maraviroc plus tenofovir. There were no serious or severe adverse events or any clinically significant changes in laboratory tests, blood pressure, or electrocardiograms.

Conclusions: Neither cotrimoxazole nor tenofovir caused a clinically significant effect on the pharmacokinetics of maraviroc. Maraviroc 300 mg b.i.d. was well tolerated when co-administered with either cotrimoxazole or tenofovir.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03135.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311416PMC
April 2008

Effects of CYP3A4 inducers with and without CYP3A4 inhibitors on the pharmacokinetics of maraviroc in healthy volunteers.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:38-46

Pfizer Global R&D, Sandwich, UK.

Aims: To assess the potential of known CYP3A4 inducers, with and without CYP3A4 inhibitors, to alter the pharmacokinetic profile of maraviroc.

Methods: Two separate, open, randomized, placebo-controlled studies were conducted in healthy subjects. Study 1 was a 28-day parallel-group study with three treatment groups of 12 subjects each. On days 1-7, all subjects received maraviroc 100 mg b.i.d.; on days 8-21, subjects received maraviroc 100 mg b.i.d. plus either rifampicin 600 mg q.d., efavirenz (EFV) 600 mg q.d., or placebo q.d. as assigned; on days 22-28, the maraviroc dose was increased to 200 mg b.i.d. for patients receiving either rifampicin or EFV. Study 2 was a 21-day, two-way crossover study with three cohorts (12 subjects per cohort). On days 1-21, subjects received maraviroc 300 mg b.i.d. and boosted lopinavir (LPV/r, lopinavir 400 mg + ritonavir 100 mg) or placebo b.i.d. in cohort 1, maraviroc 100 mg b.i.d. and boosted saquinavir (SQV/r, saquinavir 1000 mg + ritonavir 100 mg) or placebo b.i.d. in cohort 2, and maraviroc 100 mg b.i.d. and 1000 mg saquinavir + LPV/r (400 mg/100 mg) or placebo b.i.d. in cohort 3. On days 8-21, subjects in all three cohorts also received EFV 600 mg or placebo q.d.

Results: Maraviroc (100 mg b.i.d.) exposure (AUC(12) and C(max)) was reduced in the presence of rifampicin and EFV by approximately 70% and 50%, respectively. Maraviroc AUC(12) and C(max) approached preinduction values when the maraviroc dose was increased to 200 mg b.i.d. for both the rifampicin-treated and EFV-treated groups. Co-administration of LPV/r with maraviroc (300 mg b.i.d.) resulted in geometric mean ratios (GMRs) of 395% and 197% for maraviroc AUC(12) and C(max), respectively, compared with placebo; addition of EFV resulted in GMRs of 253% and 125% for AUC(12) and C(max), respectively. Co-administration of SQV/r with maraviroc (100 mg b.i.d.) resulted in GMRs of 977% and 478% for maraviroc AUC(12) and C(max), respectively, compared with placebo; addition of EFV resulted in GMRs of 500% and 226% for AUC(12) and C(max), respectively. No pharmacokinetic data are reported for cohort 3 because all subjects were discontinued during period 1 due to poor toleration of the drug regimen. There were no serious adverse events reported in either study, and most adverse events were mild or moderate in severity and resolved without intervention.

Conclusion: As expected with a CYP3A4 substrate, maraviroc exposure (C(max) and AUC(12)) was significantly reduced by the known CYP3A4 inducers, rifampicin and EFV, by approximately 70% and 50%, respectively. Upward adjustment of the maraviroc dose during co-administration with rifampicin or EFV appears to compensate for this reduction. Protease inhibitors (PIs) significantly increased maraviroc exposure; however, the addition of EFV to the maraviroc + PI regimens reduced the magnitude of PI-mediated increase in maraviroc exposure (by approximately 50%), but the net effect was still CYP3A4 inhibition.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03134.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311410PMC
April 2008

Effects of CYP3A4 inhibitors on the pharmacokinetics of maraviroc in healthy volunteers.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:27-37

Pfizer Global R&D, Sandwich, UK.

Aims: To evaluate the influence of cytochrome P450 (CYP) 3A4 inhibitors on the clinical pharmacokinetics of maraviroc, a novel CCR5 antagonist.

Methods: Four open-label, randomized, placebo-controlled studies were conducted in healthy subjects to assess the effect of separate and distinct combinations of CYP3A4 inhibitors on the steady-state pharmacokinetics of maraviroc. Study 1 was a two-way crossover study investigating the influence of saquinavir (SQV; 1200 mg t.i.d.) and ketoconazole (400 mg q.d.) on the pharmacokinetics of maraviroc (100 mg b.i.d.). All subjects received maraviroc for 7 days in both study periods. Cohort 1 subjects also received SQV or placebo and cohort 2 subjects also received ketoconazole or placebo. Study 2 was a parallel-group study including four treatment groups investigating the effects of ritonavir-boosted lopinavir (LPV/r; 400 mg/100 mg b.i.d.), ritonavir-boosted saquinavir (SQV/r; 1000 mg/100 mg b.i.d.), and low-dose ritonavir (RTV; 100 mg b.i.d.) on the steady-state pharmacokinetics of maraviroc (100 mg b.i.d.), and exploring whether maraviroc dose adjustment can compensate for interaction effects. Treatment lasted 28 days and comprised three distinct phases: (i) maraviroc alone on days 1-7; (ii) maraviroc + interactant on days 8-21; and (iii) maraviroc (adjusted dose) + interactant on days 22-28. Study 3 was a two-way crossover study investigating the effects of atazanavir (ATZ; 400 mg q.d.) and ritonavir-boosted atazanavir (ATZ/r; 300 mg/100 mg b.i.d.) on the pharmacokinetics of maraviroc (300 mg b.i.d.). All subjects received maraviroc on days 1-14 of both study periods. Subjects also received ATZ on days 1-7 and ATZ/r on days 8-14 of one treatment period, and placebo on days 1-14 of the other treatment period. Study 4 was a two-way crossover study investigating the effects of ritonavir-boosted tipranavir (TPV/r; 500 mg/200 mg b.i.d.) on the pharmacokinetics of maraviroc (150 mg b.i.d.). Subjects received maraviroc plus TPV/r or placebo on days 1-8.

Results: All of the drugs/drug combinations tested (except for TPV/r) increased maraviroc exposure, albeit to different degrees of magnitude. SQV/r caused the largest increase in maraviroc exposure (8.3-fold increase in AUC(tau)), whereas RTV caused the smallest increase in maraviroc exposure (2.6-fold increase in AUC(tau)). Downward adjustment of the maraviroc dose in study 2 during co-administration of HIV protease inhibitors was able to compensate for the interactions. TPV/r had no clinically relevant effect on maraviroc exposure at steady state. There were no treatment-related serious adverse events or discontinuations due to adverse events in any of the studies, and most adverse events were mild or moderate in severity and resolved without intervention.

Conclusions: Potent CYP3A4 inhibitors, including ketoconazole and protease inhibitors (except TPV/r), increase maraviroc exposure. Downward adjustment of the maraviroc dose during co-administration with protease inhibitors can compensate for the interaction. TPV/r does not affect the steady-state pharmacokinetics of maraviroc, and hence no dose adjustment would be warranted.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03133.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311406PMC
April 2008

Effect of maraviroc on the pharmacokinetics of midazolam, lamivudine/zidovudine, and ethinyloestradiol/levonorgestrel in healthy volunteers.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:19-26

Pfizer Global R&D, Sandwich, UK.

Aims: To assess the effect of maraviroc on the pharmacokinetics of midazolam, a sensitive probe CYP3A4 substrate; lamivudine/zidovudine, a combination of nucleoside reverse transcriptase inhibitors (NRTIs); and ethinyloestradiol/levonorgestrel, a combination oral contraceptive.

Methods: Three randomized, double-blind, placebo-controlled studies were conducted in healthy subjects to assess the effect of maraviroc on pharmacokinetics of other drugs. Two, two-period crossover studies were conducted to assess (i) the effect of steady-state maraviroc (300 mg b.i.d.) on pharmacokinetics of midazolam; and (ii) the effect of steady-state maraviroc (300 mg b.i.d.) on the pharmacokinetics of lamivudine/zidovudine. A third two-way crossover study was conducted to evaluate the effect of steady-state maraviroc (100 mg b.i.d.) on the pharmacokinetics of 30 microg ethinyloestradiol/150 microg levonorgestrel (Microgynon).

Results: The geometric mean ratios for C(max) and AUC for each of the compounds tested in the presence and absence of maraviroc were between 92% and 121%. There were no notable differences in T(max), t(1/2) or CL(R) (where measured) for any of the compounds.

Conclusions: Maraviroc had no clinically relevant effects on the pharmacokinetics of the CYP3A4 substrate midazolam, the NRTIs zidovudine/lamivudine, or the oral contraceptive steroids ethinyloestradiol and levonorgestrel.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03132.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311411PMC
April 2008

Assessment of the pharmacokinetics, safety and tolerability of maraviroc, a novel CCR5 antagonist, in healthy volunteers.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:5-18

Pfizer Global Research and Development, Sandwich, UK.

Aims: To evaluate the pharmacokinetics, safety and tolerability of single and multiple oral doses of maraviroc in healthy volunteers.

Methods: Three double-blind, placebo-controlled, dose-escalation studies with either single or multiple doses of maraviroc were conducted in healthy volunteers. Plasma and urine samples were collected to investigate the pharmacokinetics of maraviroc and evaluate any changes with respect to dose and duration/frequency of dosing. Safety and toleration of maraviroc were also assessed.

Results: Maraviroc is rapidly absorbed following oral administration, and plasma T(max) is achieved within 0.5-4.0 h postdose. Steady-state plasma concentrations are achieved after 7 consecutive days of dosing. Although the pharmacokinetics of maraviroc is nonproportional over the dose range studied (3-1200 mg), the degree of nonproportionality is small at clinically relevant doses. Renal clearance is approximately 10-12 l h(-1) and appears unaffected by increasing maraviroc doses. Maraviroc does not significantly modulate the activity of CYP2D6 or CYP3A4 at clinically relevant doses. There were no serious adverse events in any of these studies, and doses up to 900 mg were generally well tolerated, with postural hypotension being the dose-limiting event. There was no pattern or dose relationship observed with maraviroc with regard to laboratory abnormalities, including hepatic transaminases. No clinically significant increases in QTc were noted at clinically relevant doses.

Conclusions: Maraviroc is absorbed into the systemic circulation and reaches steady state by day 7 of multiple dosing. It does not significantly influence the activity of major drug-metabolizing enzymes and is well tolerated at clinically relevant doses, with most adverse events being mild or moderate.
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http://dx.doi.org/10.1111/j.1365-2125.2008.03130.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311414PMC
April 2008

A review of the clinical pharmacology of maraviroc. Introduction.

Br J Clin Pharmacol 2008 Apr;65 Suppl 1:1-4

St Stephens Aids Trust, Crusaid Research Institute, St Stephen's Centre, London, UK.

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http://dx.doi.org/10.1111/j.1365-2125.2008.03131.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311405PMC
April 2008

Efficacy of short-term monotherapy with maraviroc, a new CCR5 antagonist, in patients infected with HIV-1.

Nat Med 2005 Nov 5;11(11):1170-2. Epub 2005 Oct 5.

Department of Internal Medicine, Division of Infectious Diseases, Haus 11, University of Cologne, Joseph-Stelzmann-Strasse 9, D-50924 Cologne, Germany.

We assessed the efficacy and safety of 10-d monotherapy with the orally administered CCR5 antagonist maraviroc in 63 HIV-1-positive individuals prescreened for the absence of CXCR4-using virus. Maximum reduction in viral load occurred at a median of 10-15 d, with a mean reduction of >or=1.6 log(10) copies/ml at all twice daily doses >or=100 mg. These results provide proof of concept that CCR5 antagonism is a viable antiretroviral therapeutic approach.
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http://dx.doi.org/10.1038/nm1319DOI Listing
November 2005

Species differences in the disposition of the CCR5 antagonist, UK-427,857, a new potential treatment for HIV.

Drug Metab Dispos 2005 Apr 13;33(4):587-95. Epub 2005 Jan 13.

Department of Pharmacokinetics, Dynamics and Metabolism (IPC 664), Pfizer Global Research and Development, Sandwich, Kent, CT13 9NJ, UK.

UK-427,857 (4, 4-difluoro-N-[(1S)-3-[exo-3-(3-isopropyl-5-methyl-4H-1,2,4-triazol-4-yl)-8-azabicyclo[3.2.1]oct-8-yl]-1-phenylpropyl]cyclohexanecarboxamide) is a novel CCR5 antagonist undergoing investigation for use in the treatment of human immunodeficiency virus (HIV) infection. Pharmacokinetic and metabolism studies have been performed in mouse, rat, dog, and human after single and multiple administration by oral and intravenous routes. The compound has physicochemical properties that are borderline for good pharmacokinetics, being moderately lipophilic (log D(7.4) 2.1) and basic (pK(a) 7.3), possessing a number of H-bonding functionalities, and with a molecular weight of 514. The compound was incompletely absorbed in rat (approximately 20-30%) but well absorbed in dog (>70%). Based on in vitro studies in Caco-2 cells, UK-427,857 has relatively poor membrane permeability, and transcellular flux is enhanced in the presence of inhibitors of P-glycoprotein. Further evidence for the involvement of P-glycoprotein in restricting the oral absorption of UK-427,857 was obtained in P-glycoprotein null mice (mdr1a/mdr1b knockout). In these animals, AUC after oral administration was 3-fold higher than in control animals. In oral dose escalation studies in humans, the compound demonstrated nonlinear pharmacokinetics, with increased dose-normalized exposure with increased dose size, consistent with saturation of P-glycoprotein. The oral dose-exposure relationship of UK-427,857 in humans was not reflected in either rat or dog. In animal species and humans, UK-427,857 undergoes some metabolism, with parent compound the major component present in the systemic circulation and excreta. Elimination of radioactive dose was primarily via the feces. In rat, parent compound was secreted via bile and directly into the gastrointestinal tract. Metabolites were products of oxidative metabolism and showed a high degree of structural consistency across species.
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http://dx.doi.org/10.1124/dmd.104.002626DOI Listing
April 2005

Pharmacokinetics, pharmacodynamics, and safety of the 5-HT(1B/1D) agonist eletriptan following intravenous and oral administration.

J Clin Pharmacol 2002 May;42(5):528-39

Clinical Sciences, Pfizer Global Research and Development, Sandwich, Kent, United Kingdom.

Four separate studies were conducted to examine the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of eletriptan, a 5-HT(1B/1D) receptor agonist being developed for the treatment of migraines, after oral and intravenous administration. Fifty-five males received oral (1.5-30 mg or 30-120 mg) or intravenous (1.67-50 microg/kg or 50-102 microg/kg) eletriptan in four double- and single-blind, placebo-controlled, ascending-dose crossover studies. The maximum plasma concentration (Cmax) and area under the concentration curve (AUC) appeared linear over all dose ranges, with an apparent terminal half-life of 4 to 5 hours. Clearance and volume of distribution remained constant with dose. The time to first occurrence of Cmax (tmax) for oral eletriptan was approximately 1 hour and was unaffected by dose. Comparison of AUC values suggested an absolute bioavailability of approximately 50%. A linear PK/PD model, fitted to the data, predicted small, transient elevations in diastolic blood pressure following eletriptan doses > or = 60 mg. These effects were considered unlikely to be clinically significant. Eletriptan was well tolerated, and treatment-related adverse events were mild to moderate and transient. These PK properties should result in eletriptan having a rapid onset and sustained duration of action in terms of migraine efficacy.
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http://dx.doi.org/10.1177/00912700222011580DOI Listing
May 2002