Pharmacokinetic-pharmacodynamic (dipeptidyl peptidase-4 inhibition) model to support dose rationale in diabetes patients, including those with renal impairment, for once-weekly administered omarigliptin.

AIMS: To characterize the population pharmacokinetics (PK) and pharmacodynamics (PD) of the once-weekly dipeptidyl peptidase-4 (DPP-4) inhibitor omarigliptin in healthy subjects and patients with type 2 diabetes mellitus, and use these models to support the dosing recommendation for patient labelling including patients with renal impairment. METHODS: PK and PD were assessed from a total of 9827 omarigliptin concentrations collected from 1387 healthy subjects and patients participating in Phase 1, 2 and 3 studies examining single- or multiple-dose weekly administration of omarigliptin at doses ranging from 0.25 to 400 mg. Population PK and PD analyses were performed using nonlinear mixed effect modelling. RESULTS: A semi-mechanistic 2-compartment model with linear unbound clearance and concentration-dependent binding of omarigliptin to the DPP-4 enzyme in both the central and peripheral compartments adequately described omarigliptin PK. Key covariates on omarigliptin PK included reduced unbound clearance with renal impairment. A direct effect sigmoid maximum inhibitory efficacy model adequately described the relationship between omarigliptin plasma concentrations and DPP-4 inhibition. These models supported the current Japan label instructions that the approved omarigliptin 25-mg once-weekly dose be halved in patients with severe renal impairment and in those with end-stage renal disease. Also, if patients missed a dose, the next dose of omarigliptin should be taken as soon as remembered up to and including the day before the next scheduled dose. No other clinically important covariates were identified. CONCLUSION: The models in the present analysis adequately described PK and PD characteristics of omarigliptin and supported the dosing and administration section of the omarigliptin label.

Ceftazidime-Avibactam Population Pharmacokinetic Modeling and Pharmacodynamic Target Attainment Across Adult Indications and Patient Subgroups.

Ceftazidime-avibactam is a novel ß-lactam/ß-lactamase inhibitor combination for the treatment of serious infections caused by resistant gram-negative pathogens. Population pharmacokinetic (PopPK) models were built to incorporate pharmacokinetic (PK) data from five phase III trials in patients with complicated intra-abdominal infection (cIAI), complicated urinary tract infection (cUTI), or nosocomial (including ventilator-associated) pneumonia. Ceftazidime and avibactam pharmacokinetics were well-described by two-compartment disposition models, with creatinine clearance (CrCL) the key covariate determining clearance variability. Steady-state ceftazidime and avibactam exposure for most patient subgroups differed by ≤ 20% vs. healthy volunteers. Probability of PK/pharmacodynamic (PD) target attainment (free plasma ceftazidime > 8 mg/L and avibactam > 1 mg/L for ≥ 50% of dosing interval) was ≥ 94.9% in simulations for all patient subgroups, including indication and renal function categories. No exposure-microbiological response relationship was identified because target exposures were achieved in almost all patients. These modeling results support the approved ceftazidime-avibactam dosage regimens (2000-500 mg every 8 hours, adjusted for CrCL ≤ 50 mL/min).

Predicting complications with pretreatment testing in infantile haemangioma treated with oral propranolol.

BACKGROUND: Since 2008, orally administered propranolol has rapidly gained acceptance as the preferred therapy for haemangiomas, and is usually initiated by ophthalmologists, dermatologists or plastic surgeons who do not routinely use propranolol for any other indication. During the initial years when experience was limited, most healthcare professionals justifiably adopted a cautious approach when initiating and monitoring treatment. A consensus recommendation from the American Society of Dermatologists suggests routine observation, monitoring and cardiology assessments prior to propranolol initiation. AIM: This study aims to analyse treatment initiation in a large tertiary children's hospital and investigate the value of pretreatment testing in predicting commonly seen adverse reactions of propranolol. METHOD: 104 eligible patients treated between January 2009 and July 2012 were included. All patients underwent pretesting either with protocol A (administration of test dose with routine observations) or protocol B (cardiology clinic assessment, including two-dimensional echocardiography without test dose). RESULTS: 38.5% (40/104) of patients developed adverse reactions during treatment; however, there were no severe or life-threatening reactions. Protocol A has a sensitivity of 0 (95% CI 0 to 0.17) and specificity of 0.95 (95% CI 0.83 to 0.99). Protocol B has a sensitivity of 0.07 (95% CI 0 to 0.34) and specificity of 0.86 (95% CI 0.63 to 0.96). CONCLUSIONS: The predictive values of both protocols for the commonly observed adverse reactions are low. In this series, there is no evidence to suggest that routine pretreatment testing before propranolol initiation is of any value in otherwise healthy children.

Pharmacokinetics and Exposure-Response Relationships of Dasotraline in the Treatment of Attention-Deficit/Hyperactivity Disorder in Adults.

BACKGROUND AND OBJECTIVES: Dasotraline is a novel inhibitor of dopamine and norepinephrine reuptake currently being investigated in clinical studies for the treatment of attention-deficit/hyperactivity disorder (ADHD). Uniquely, relative to current ADHD medications, dasotraline has a slow absorption and long elimination half-life. Here we relate the pharmacokinetics and pharmacodynamics of dasotraline to reduction in ADHD symptoms based on simulated clinical trial outcomes. METHODS: Dasotraline pharmacokinetics were analyzed by population pharmacokinetic methodologies using data collected from 395 subjects after single or multiple oral dose administrations ranging from 0.2 to 36 mg (three phase I studies and one phase II ADHD study). Population pharmacokinetic and pharmacodynamic models related individual dasotraline exposures to norepinephrine metabolite 3,4-dihydroxyphenylglycol (DHPG) concentrations, ADHD symptoms, and study discontinuation (probability of dropout). RESULTS: Dasotraline pharmacokinetics were described by a one-compartment model with dual (linear plus nonlinear) elimination. In an ADHD population treated with dasotraline 4 or 8 mg/day, dasotraline was characterized by a mean apparent half-life of 47 h and plasma concentrations reached steady-state by 10 days of dosing. A population pharmacokinetic and pharmacodynamic model of DHPG indicated clinically significant norepinephrine transporter inhibition was achieved as a function of time-matched dasotraline concentrations. Dasotraline exposure reduced ADHD symptoms in a sigmoid E max time-course model. Clinical trial simulations described the effects of dose, duration, and sample size on clinical outcomes. CONCLUSION: These results related dasotraline pharmacokinetics to pharmacological activity in ADHD, and support the novel concept that maintaining constant, steady-state dopamine and norepinephrine reuptake inhibition throughout a 24-h dosing interval is a novel pharmacological approach to the management of ADHD symptoms. Clinicaltrials.gov identifier: NCT01692782.

Factors Affecting Medical Students' Uptake of the 2009 Pandemic Influenza A (H1N1) Vaccine.

Background. Pandemic influenza vaccination rate amongst healthcare workers in England 2009/2010 was suboptimal (40.3%). Targeting medical students before they enter the healthcare workforce is an attractive future option. This study assessed the H1N1 vaccine uptake rate amongst medical students and factors that influenced this. Methods. Anonymised, self-administered questionnaire at a medical school. Results. The uptake rate amongst 126 medical students offered the vaccine was 49.2% and intended uptake amongst 77 students was 63.6%. Amongst those offered the vaccine, the strongest barriers to acceptance were fear of side effects (67.9%), lack of vaccine information (50.9%), lack of perceived risk (45.3%), and inconvenience (35.8%). Having a chronic illness (OR 3.4 (95% CI 1.2-10.2)), 4th/5th year of study (OR 3.0 (95% CI 1.3-7.1)), and correct H1N1 knowledge (OR 2.6 (95% CI 1.1-6.0)) were positively associated with uptake. Non-white ethnicity was an independent negative predictor of uptake (OR 0.4 (95% CI 0.2-0.8)). Students who accepted the H1N1 vaccine were three times more likely (OR 3.1 (95% CI 1.2-7.7)) to accept future seasonal influenza vaccination. Conclusion. Efforts to increase uptake should focus on routine introduction of influenza vaccine and creating a culture of uptake during medical school years, evidence-based education on vaccination, and improving vaccine delivery.

Phase I pharmacologic and pharmacodynamic study of the gamma secretase (Notch) inhibitor MK-0752 in adult patients with advanced solid tumors.

PURPOSE: Aberrant Notch signaling has been implicated in the pathogenesis of many human cancers. MK-0752 is a potent, oral inhibitor of γ-secretase, an enzyme required for Notch pathway activation. Safety, maximum-tolerated dose, pharmacokinetics (PKs), pharmacodynamics, and preliminary antitumor efficacy were assessed in a phase I study of MK-0752. PATIENTS AND METHODS: MK-0752 was administered in three different schedules to patients with advanced solid tumors. Hair follicles were collected at higher dose levels to assess a gene signature of Notch inhibition. RESULTS: Of 103 patients who received MK-0752, 21 patients received a continuous once-daily dosing at 450 and 600 mg; 17 were dosed on an intermittent schedule of 3 of 7 days at 450 and 600 mg; and 65 were dosed once per week at 600, 900, 1,200, 1,500, 1,800, 2,400, 3,200, and 4,200 mg. The most common drug-related toxicities were diarrhea, nausea, vomiting, and fatigue. PKs (area under the concentration-time curve and maximum measured plasma concentration) increased in a less than dose proportional manner, with a half-life of approximately 15 hours. Significant inhibition of Notch signaling was observed with the 1,800- to 4,200-mg weekly dose levels, confirming target engagement at those doses. One objective complete response and an additional 10 patients with stable disease longer than 4 months were observed among patients with high-grade gliomas. CONCLUSION: MK-0752 toxicity was schedule dependent. Weekly dosing was generally well tolerated and resulted in strong modulation of a Notch gene signature. Clinical benefit was observed, and rational combination trials are currently ongoing to maximize clinical benefit with this novel agent.

Pharmacodynamic analysis of recombinant human erythropoietin effect on reticulocyte production rate and age distribution in healthy subjects.

OBJECTIVE: To evaluate the effect of recombinant human erythropoietin (rHuEPO) on the reticulocyte production rate and age distribution in healthy subjects. METHODS: Extensive pharmacokinetic and pharmacodynamic data collected from 88 subjects who received a single subcutaneous dose of rHuEPO (dose range 20-160 kIU) were analysed. Four nonlinear mixed-effects models were evaluated to describe the time course of the percentage of reticulocytes and their age distribution in relation to rHuEPO pharmacokinetics. Model A accounted for stimulation of the production of progenitor cells in bone marrow, and model B implemented shortening of differentiation and maturation times of early progenitors in bone marrow. Model C was the combination of models A and B, and model D was the combination of model A with an increase in the maturation times of the circulating reticulocytes. Model evaluation was performed using goodness-of-fit plots, a nonparametric bootstrap and a posterior predictive check. RESULTS: Model D was selected as the best model, and evidenced accurate and precise estimation of model parameters and prediction of the time course of the percentage of reticulocytes. At baseline, the estimated circulating reticulocyte maturation time was 2.6 days, whereas the lifespan of the precursors in the bone marrow was about 5 days. The rHuEPO potency for the stimulatory effect (7.61 IU/L) was higher than that for the increase in reticulocyte maturation times (56.3 IU/L). There was a significant 1- to 2-day lag time in the reticulocyte response. The effect of rHuEPO on the reticulocyte age distribution consisted of a transient increase in the reticulocyte maturation time from baseline up to 6-7 days, occurring 1 day after administration. The dose-dependent amplitude of the changes in the age distribution lasted for 12-14 days. The model-predicted peak increase in the reticulocyte release rate ranged from 140% to 160% of the baseline value and was maximal on days 7-8 following rHuEPO administration. CONCLUSIONS: A semiphysiological model quantifying the effect of rHuEPO on the reticulocyte production rate and age distribution was developed. The validated model predicts that rHuEPO increases the reticulocyte production rate and modifies the reticulocyte age distribution in a dose-dependent manner.

Pharmacokinetic simulation for switching from galantamine immediate-release to extended-release formulation.

OBJECTIVE: To demonstrate using pharmacokinetic (PK) modeling and simulation, that the PK that the PK parameters for drug exposure with galantamine parameters for drug exposure with galantamine immediate-release (IR) tablet and galantamine extended-release (ER) capsule are comparable in patients with Alzheimer's disease (AD) during in patients with Alzheimer's disease (AD) during the switch from twice-daily IR tablet at steady state to the new once-daily ER capsule, and to support a recommendation that patients receiving the IR tablet at steady state can be successfully switched to the ER capsule at the same daily dosage with no titration period. METHODS: Simulations were performed using a population PK model developed from clinical studies with IR galantamine in the target AD population, in combination with IR and ER absorption parameters obtained from a PK study in healthy volunteers which showed similar results. PK simulations were performed for the switch from IR tablet 8 mg b.i.d. to ER capsule 16 mg q.d. and from IR tablet 12 mg b.i.d. to ER capsule 24 mg q.d. RESULTS: This simulation predicted that patients switched from the IR tablet to the ER capsule, the PK parameters for drug exposure on the first day of ER treatment would be similar to those of IR treatment at steady state. After steady state was achieved with ER galantamine, values for peak concentration and trough concentration were slightly lower (5% and 18%, respectively) than those seen at steady state for IR galantamine; this finding is considered to have no clinical implications. Area under the curve (AUC) with ER galantamine was similar to that seen at steady state with IR galantamine. CONCLUSIONS: These results suggest that no titration period is required in patients receiving stable doses of twice-daily IR galantamine who are switched to once-daily ER galantamine. The once-daily dosage regimen of ER galantamine without a titration period should prove convenient for AD patients and their caregivers and should increase treatment compliance.

Distinguishing animal subsets in toxicokinetic studies: comparison of non-linear mixed effects modelling with non-compartmental methods.

The purpose of this study was to compare the ability of non-compartmental analysis and compartmental mixed effects modelling (MEM) to determine the existence and magnitude of exposure differences (i.e. exposure ratio estimates) between subsets of animals during destructive toxicokinetic studies. Data from five toxicokinetic studies of an experimental compound were analysed using a linear trapezoidal calculation of the area under the curve (non-compartmental analysis) or modelled using MEM. With the non-compartmental method the Bailer-Satterthwaite approximation was used to construct confidence intervals around the exposure estimates of each subset of animals and these were used to determine if exposure differed between the subsets. The MEM analyses were performed on the full datasets and on datasets with arbitrary reductions in the number of animal replicates. With MEM, additional model parameters were used to differentiate between subsets of animals, and were incorporated only if they were justified statistically. Estimates of the existence and magnitude of exposure differences between animal subsets were similar with the two techniques. The MEM analyses were influenced only marginally by substantial reductions in the number of animals studied and were less compromised by extremely limited or unbalanced data. These analyses show that MEM and non-compartmental methods are similarly effective at detecting exposure differences between animal subsets in toxicokinetic studies. Estimates provided by both methods were influenced by the degree of variance in the data. These results support the proposition that it may be possible to reduce the number of animals employed in toxicokinetic studies if MEM is used.