Bioequivalence of Two Tiotropium Dry Powder Inhalers and the Utility of Realistic Impactor Testing.

Introduction: Inhaled antimuscarinics are a cornerstone of the management of chronic obstructive pulmonary disease. This article details a series of five pharmacokinetic (PK) studies comparing a generic tiotropium dry powder inhaler (DPI) to Spiriva HandiHaler, the realistic in vitro methods used to support those studies, and the related in vitro-in vivo correlations (IVIVCs). Methods: All five PK studies were of open-label, single-dose, crossover design with test and reference treatments administered to healthy subjects. Following unexpected results in the first three PK studies, a realistic impactor method was developed comprising an Oropharyngeal Consortium (OPC) mouth-throat and simulated inspiratory profiles in conjunction with a Next Generation Impactor (NGI). Mass fractions and the in vitro whole lung dose were estimated for the test product and Spiriva® HandiHaler® using this method, and IVIVCs derived. Results: Bioequivalence could not be demonstrated for Cmax in the first three PK studies (test/reference ratios ranging from 83.1% to 131.8%), although was observed for AUCt. Reanalysis of the corresponding biobatches with the realistic NGI method revealed in vitro ratios aligned with these PK data (in contrast to the compendial NGI data) and thus inadvertent selection of "mismatched" biobatches. Two further PK studies were undertaken, supported by the realistic NGI method. With the comparison of test and reference products similarly positioned within their respective product performance distributions, bioequivalence was confirmed in both studies. IVIVCs based on mass fractions as per the realistic NGI method were robust and highly predictive of PK outcomes. Conclusions: The test tiotropium DPI and Spiriva HandiHaler were bioequivalent when equitable biobatch comparisons, based on realistic NGI testing, were performed. The observations from this program support the utility of realistic test methods for inhaled product development.

Population Pharmacokinetics of Ibrutinib in Healthy Adults.

BACKGROUND AND OBJECTIVES: Ibrutinib is an antineoplastic agent that reduces B-cell proliferation by inhibiting Bruton's tyrosine kinase. We describes population pharmacokinetics of ibrutinib in healthy adults, and explores potential patient characteristics associated with ibrutinib pharmacokinetics. METHODS: A population pharmacokinetic modeling approach was applied to 39 healthy subjects. Modeling was performed using Monolix (v.2019R2). Serial blood samples to measure the plasma ibrutinib concentration were collected following the oral administration of 140 mg ibrutinib on two different occasions under fasting conditions. Demographic and clinical information were evaluated as possible predictors of ibrutinib pharmacokinetics during model development. Simulations (using mlxR: R package v.4.0.2) following the administration of therapeutic doses were performed to explore the clinical implications of identified covariates on ibrutinib steady-state concentrations. RESULTS: A two-compartment model with zero order absorption best fit the data. Inter-individual and inter-occasion variability were quantified by the proposed model. We identified smoking status as a significant covariate associated with ibrutinib clearance. Smoking was found to increase ibrutinib clearance by approximately 60%, which resulted in a reduction in simulated steady-state concentrations by around 40%. CONCLUSION: The model can be used to simulate clinical trials or various dosing scenarios. The proposed model can be used to optimize ibrutinib dosing based on the smoking status.

The Influence of Oily Vehicle Composition and Vehicle-Membrane Interactions on the Diffusion of Model Permeants across Barrier Membranes.

In many instances, one or more components of a pharmaceutical or cosmetic formulation is an oil. The aims of this study were two-fold. First, to examine the potential of preferential uptake of one oily vehicle component over another into a model barrier membrane (silicone) from blended vehicles (comprising two from the common excipients isohexadecane (IHD), hexadecane (HD), isopropyl myristate (IPM), oleic acid (OA) and liquid paraffin). Second, to study the effect of membrane-vehicle interactions on the diffusion of model permeants (caffeine (CF), methyl paraben (MP) and butyl paraben (BP)) from blended vehicles. Selective sorption and partition of some oils (especially IHD and IPM) at the expense of other oils (such as OA) was demonstrated to take place. For example, the membrane composition of IHD was enriched compared to a donor solution of IHD-OA: 41%, 63% and 82% IHD, compared to donor solution composition of 25%, 50% and 75% IHD, respectively. Pre-soaking the membrane in IHD, HD or LP, rather than phosphate buffer, enhanced the flux of MP through the membrane by 2.6, 1.7 and 1.3 times, respectively. The preferential sorption of individual oil components from mixtures altered the barrier properties of silicone membrane, and enhanced the permeation of CF, MP and BP, which are typically co-formulated in topical products.

Multivariate Analytical Approaches to Identify Key Molecular Properties of Vehicles, Permeants and Membranes That Affect Permeation through Membranes.

There has been considerable recent interest in employing computer models to investigate the relationship between the structure of a molecule and its dermal penetration. Molecular permeation across the epidermis has previously been demonstrated to be determined by a number of physicochemical properties, for example, the lipophilicity, molecular weight and hydrogen bonding ability of the permeant. However little attention has been paid to modeling the combined effects of permeant properties in tandem with the properties of vehicles used to deliver those permeants or to whether data obtained using synthetic membranes can be correlated with those obtained using human epidermis. This work uses Principal Components Analysis (PCA) to demonstrate that, for studies of the diffusion of three model permeants (caffeine, methyl paraben and butyl paraben) through synthetic membranes, it is the properties of the oily vehicle in which they are applied that dominated the rates of permeation and flux. Simple robust and predictive descriptor-based quantitative structure-permeability relationship (QSPR) models have been developed to support these findings by utilizing physicochemical descriptors of the oily vehicles to quantify the differences in flux and permeation of the model compounds. Interestingly, PCA showed that, for the flux of co-applied model permeants through human epidermis, the permeation of the model permeants was better described by a balance between the physicochemical properties of the vehicle and the permeant rather than being dominated solely by the vehicle properties as in the case of synthetic model membranes. The important influence of permeant solubility in the vehicle along with the solvent uptake on overall permeant diffusion into the membrane was substantiated. These results confirm that care must be taken in interpreting permeation data when synthetic membranes are employed as surrogates for human epidermis; they also demonstrate the importance of considering not only the permeant properties but also those of both vehicle and membrane when arriving at any conclusions relating to permeation data.

Establishing the importance of oil-membrane interactions on the transmembrane diffusion of physicochemically diverse compounds.

The diffusion process through a non-porous barrier membrane depends on the properties of the drug, vehicle and membrane. The aim of the current study was to investigate whether a series of oily vehicles might have the potential to interact to varying degrees with synthetic membranes and to determine whether any such interaction might affect the permeation of co-formulated permeants: methylparaben (MP); butylparaben (BP) or caffeine (CF). The oils (isopropyl myristate (IPM), isohexadecane (IHD), hexadecane (HD), oleic acid (OA) and liquid paraffin (LP)) and membranes (silicone, high density polyethylene and polyurethane) employed in the study were selected such that they displayed a range of different structural, and physicochemical properties. Diffusion studies showed that many of the vehicles were not inert and did interact with the membranes resulting in a modification of the permeants' flux when corrected for membrane thickness (e.g. normalized flux of MP increased from 1.25±0.13µgcm(-1)h(-1) in LP to 17.94±0.25µgcm(-1)h(-1)in IPM). The oils were sorbed differently to membranes (range of weight gain: 2.2±0.2% for polyurethane with LP to 105.6±1.1% for silicone with IHD). Membrane interaction was apparently dependent upon the physicochemical properties including; size, shape, flexibility and the Hansen solubility parameter values of both the membranes and oils. Sorbed oils resulted in modified permeant diffusion through the membranes. No simple correlation was found to exist between the Hansen solubility parameters of the oils or swelling of the membrane and the normalized fluxes of the three compounds investigated. More sophisticated modelling would appear to be required to delineate and quantify the key molecular parameters of membrane, permeant and vehicle compatibility and their interactions of relevance to membrane permeation.