Pharmacokinetics of Orally Inhaled Drug Products

Microstructural insight into inhalation powder blends through correlative multi-scale X-ray computed tomography

Dry powder inhalers (DPI) are important for topical drug delivery to the lungs, but characterising the pre-aerosolised powder microstructure is a key initial step in understanding the post-aerosolised blend performance. In this work, we characterise the pre-aerosolised 3D microstructure of an inhalation blend using correlative multi-scale X-ray Computed Tomography (XCT), identifying lactose and drug-rich phases at multiple length scales on the same sample. The drug-rich phase distribution across the sample is shown to be homogeneous on a bulk scale but heterogeneous on a particulate scale, with individual clusters containing different amounts of drug-rich phase, and different parts of a carrier particle coated with different amounts of drug-rich phase. Simple scalings of the drug-rich phase thickness with carrier particle size are used to derive the drug-proportion to carrier particle size relationship. This work opens new doors to micro-structural assessment of inhalation powders that could be invaluable for bioequivalence assessment of dry powder inhalers.

Bioequivalence study of ipratropium bromide inhalation aerosol using PBPK modelling

Aims

Systemic pharmacokinetic (PK) studies can reflect the overall exposure of orally inhaled drug Products (OIDPs) in the blood after inhalation into the lung and can be used to evaluate the bioequivalence of test and reference products. The aim of this article is: (1) to study the PK characteristics and bioequivalence of ipratropium bromide (IB) inhalation aerosol, reference and test products in healthy Chinese subjects; (2) to establish a physiologically based pharmacokinetic (PBPK) model and verify the accuracy of the model in predicting bioequivalence; (3) attempt to use the model to predict the regional distribution of particles in the lung after inhalation, and discuss the effect of gastrointestinal drug absorption of IB on systemic exposure.

Methods

The study involved two clinical studies. Clinical study-1 (registration number: CTR20201284) was used with non-clinical data to construct and validate a PBPK model in the B²O simulator, a web-based virtual drug development platform. This model assessed different test and reference products' bioequivalence. Results were compared to a second clinical study (Clinical study-2: registration number CTR20202291). The particles' regional distribution in the lung and the gastrointestinal absorption effect on systemic exposure were discussed based on the simulation results.

Results

The established PBPK model successfully simulated the in vivo PK characteristics of IB inhalation aerosol, with r ² close to 1. Gastrointestinal absorption had a negligible effect on systemic exposure. Particles accumulated in the alveolar area were cleared within an hour, followed by particles in the bronchioles and bronchi.

Conclusion

This model provided a reliable method for exploring the correlation between in vitro and in vivo PK studies of IB inhalation aerosols. According to the simulation results, the test and reference products were bioequivalent.

Scientific and regulatory activities initiated by the U.S. Food and drug administration to foster approvals of generic dry powder inhalers: Bioequivalence perspective

Regulatory science for generic dry powder inhalers (DPIs) in the United States (U.S.) has evolved over the last decade. In 2013, the U.S. Food and Drug Administration (FDA) published the draft product-specific guidance (PSG) for fluticasone propionate and salmeterol xinafoate inhalation powder. This was the first PSG for a DPI available in the U.S., which provided details on a weight-of-evidence approach for establishing bioequivalence (BE). A variety of research activities including in vivo and in vitro studies were used to support these recommendations, which have led to the first approval of a generic DPI in the U.S. for fluticasone propionate and salmeterol xinafoate inhalation powder in January of 2019. This review describes the scientific and regulatory activities that have been initiated by FDA to support the current BE recommendations for DPIs that led to the first generic DPI approvals, as well as research with novel in vitro and in silico methods that may potentially facilitate generic DPI development and approval.

Advances and future perspectives in epithelial drug delivery

Epithelial surfaces protect exposed tissues in the body against intrusion of foreign materials, including xenobiotics, pollen and microbiota. The relative permeability of the various epithelia reflects their extent of exposure to the external environment and is in the ranking: intestinal≈ nasal ≥ bronchial ≥ tracheal > vaginal ≥ rectal > blood-perilymph barrier (otic), corneal > buccal > skin. Each epithelium also varies in their morphology, biochemistry, physiology, immunology and external fluid in line with their function. Each epithelium is also used as drug delivery sites to treat local conditions and, in some cases, for systemic delivery. The associated delivery systems have had to evolve to enable the delivery of larger drugs and biologicals, such as peptides, proteins, antibodies and biologicals and now include a range of physical, chemical, electrical, light, sound and other enhancement technologies. In addition, the quality-by-design approach to product regulation and the growth of generic products have also fostered advancement in epithelial drug delivery systems.

Development of a novel method for the continuous blending of carrier-based dry powders for inhalation using a co-rotating twin-screw extruder

Twin-screw extruders are useful in tuning certain product characteristics due to the ability to greatly modify screw profiles as well as operating parameters. However, their use has not yet been applied to dry powder inhalation. In this study the feasibility of using a twin-screw extruder to blend dry powders for inhalation was assessed. Micronized rifampicin (1%) was used as a model drug with lactose carrier (median size ∼ 44 µm) and 0.4% magnesium stearate as a multi-functional ternary agent. Blend performance was compared with low shear (Turbula®) batch mixing. Similar blend uniformity and aerosol performance was observed, indicating the twin-screw extruder successfully functions as a mixer for dry powders for inhalation. The ability to utilize the twin-screw extruder as a continuous mixer leads to new opportunities in the continuous manufacturing of powders for inhalation.

Assessment of the predictive capability of modelling and simulation to determine bioequivalence of inhaled drugs: A systematic review

OBJECTIVES

There are a multitude of different modelling techniques that have been used for inhaled drugs. The main objective of this review was to conduct an exhaustive survey of published mathematical models in the area of asthma and chronic obstructive pulmonary disease (COPD) for inhalation drugs. Additionally, this review will attempt to assess the applicability of these models to assess bioequivalence (BE) of orally inhaled products (OIPs).

EVIDENCE ACQUISITION

PubMed, Science Direct, Web of Science, and Scopus databases were searched from 1996 to 2020, to find studies that described mathematical models used for inhaled drugs in asthma/COPD.

RESULTS

50 articles were finally included in this systematic review. This research identified 22 articles on in silico aerosol deposition models, 20 articles related to population pharmacokinetics and 8 articles on physiologically based pharmacokinetic modelling (PBPK) modelling for inhaled drugs in asthma/COPD. Among all the aerosol deposition models, computational fluid dynamics (CFD) simulations are more likely to predict regional aerosol deposition pattern in human respiratory tracts. Across the population PK articles, body weight, gender, age and smoking status were the most common covariates that were found to be significant. Further, limited published PBPK models reported approximately 29 parameters relevant for absorption and distribution of inhaled drugs. The strengths and weaknesses of each modelling technique has also been reviewed.

CONCLUSION

Overall, while there are different modelling techniques that have been used for inhaled drugs in asthma and COPD, there is very limited application of these models for assessment of bioequivalence of OIPs. This review also provides a ready reference of various parameters that have been considered in various models which will aid in evaluation if one model or hybrid in silico models need to be considered when assessing bioequivalence of OIPs.

Performance of Multiple-Batch Approaches to Pharmacokinetic Bioequivalence Testing for Orally Inhaled Drug Products with Batch-to-Batch Variability

Batch-to-batch pharmacokinetic (PK) variability of orally inhaled drug products has been documented and can render single-batch PK bioequivalence (BE) studies unreliable; results from one batch may not be consistent with a repeated study using a different batch, yet the goal of PK BE is to deliver a product comparison that is interpretable beyond the specific batches used in the study. We characterized four multiple-batch PK BE approaches to improve outcome reliability without increasing the number of clinical study participants. Three approaches include multiple batches directly in the PK BE study with batch identity either excluded from the statistical model (“Superbatch”) or included as a fixed or random effect (“Fixed Batch Effect,” “Random Batch Effect”). A fourth approach uses a bio-predictive in vitro test to screen candidate batches, bringing the median batch of each product into the PK BE study (“Targeted Batch”). Three of these approaches (Fixed Batch Effect, Superbatch, Targeted Batch) continue the single-batch PK BE convention in which uncertainty in the Test/Reference ratio estimate due to batch sampling is omitted from the Test/Reference confidence interval. All three of these approaches provided higher power to correctly identify true bioequivalence than the standard single-batch approach with no increase in clinical burden. False equivalence (type I) error was inflated above the expected 5% level, but multiple batches controlled type I error better than a single batch. The Random Batch Effect approach restored 5% type I error, but had low power for small (e.g., <8) batch sample sizes using standard [0.8000, 1.2500] bioequivalence limits.

Batch Selection via In Vitro/In Vivo Correlation in Pharmacokinetic Bioequivalence Testing

Pharmacokinetic differences between manufacturing batches, well established for inhaled drug products, preclude control of patient risk in the customary two-way (single batch) pharmacokinetic bioequivalence crossover design if batches are randomly chosen. European regulators have recommended selecting a "typical" in vitro batch to represent each product in pharmacokinetic bioequivalence testing. We explored the feasibility of this approach to control patient risk (the "false equivalence", or Type I, error rate). The probability of achieving a Test/Reference 90% confidence interval within (0.80, 1.25) for a true (non-equivalent) value of 1.25 was simulated for a two-way crossover design using the median in vitro batch across a range of number of in vitro batches, in vitro/in vivo correlation (IVIVC) quality (correlation coefficient, r, of zero to one), and within-subject between-batch pharmacokinetic variability. Even under extremely optimistic conditions, e.g., r=0.95 and >100 batches per product screened in vitro, patient risk for typical between-batch variability levels remained at least threefold higher than the 5% regulatory expectation for the significance level (the false equivalence error rate) of the pharmacokinetic bioequivalence test. This elevated error rate in bioequivalence decision-making occurs because of incomplete confidence that the true product average has been identified, and, importantly, omission of this uncertainty from the bioequivalence confidence interval.

Asthma and Chronic Obstructive Pulmonary Disease as a Comorbidity and Association with the Choice of Antidementia Medication Among Persons with Alzheimer's Disease

BACKGROUND

Asthma and chronic obstructive pulmonary disease (COPD) are common comorbidities in persons with Alzheimer's disease (AD). However, pharmacotherapy of these diseases may have opposite mechanisms of action; anticholinergics in asthma/COPD and acetylcholinesterase inhibitors (AChEI) in AD.

OBJECTIVE

To investigate whether existing asthma/COPD affects the choice of AD medication, and the survival of the patients with AD.

METHODS

In this retrospective cohort study, data from the MEDALZ-study, which includes all community-dwelling persons with AD during 2005-2011 in Finland (n = 70718) was utilized. Persons with asthma/COPD (N = 7211) were defined as having a special reimbursement for asthma/COPD, or long-term use (≥250 days) of inhaled anticholinergics, inhaled corticosteroids, or leukotriene antagonists during the year before AD diagnosis. We compared persons with and without asthma/COPD regarding the choice of the initial antidementia medication (AChEI versus memantine) with logistic regression and mortality with Cox regression model during the follow-up (up to end of 2015).

RESULTS

Memantine was favored over AChEIs as first-line treatment to AD in persons with asthma/COPD compared to those without asthma/COPD (odds ratio 1.23, 95% confidence interval (CI) 1.15-1.31). Memantine was also more commonly used among those who used multiple asthma/COPD medications (7.9% of memantine initiators used ≥3 asthma/COPD medications compared with 5.5% of those who initiated with AChEI). Mortality was higher in persons with asthma/COPD compared to those without asthma/COPD (adjusted hazard ratio 1.10, 95% CI 1.07-1.13).

CONCLUSION

More frequent use of memantine instead of AChEI may result from an attempt to prevent possible worsening of asthma/COPD by AChEIs. Vulnerable persons with both AD and asthma/COPD need individually assessed pharmacotherapy for their medical conditions.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

The Role of ICS/LABA Fixed-Dose Combinations in the Treatment of Asthma and COPD: Bioequivalence of a Generic Fluticasone Propionate-Salmeterol Device

Both asthma and chronic obstructive pulmonary disease (COPD) are inflammatory chronic respiratory conditions with high rates of morbidity and mortality worldwide. The objectives of this review are to briefly describe the pathophysiology and epidemiology of asthma and COPD, discuss guideline recommendations for uncontrolled disease, and review a new generic option for the treatment of asthma and COPD. Although mild forms of these diseases may be controlled with as-needed pharmacotherapy, uncontrolled or persistent asthma and moderate or severe COPD uncontrolled by bronchodilators with elevated eosinophilia or frequent exacerbations may require intervention with combination therapy with inhaled corticosteroids (ICS) and long-acting beta agonists (LABAs), according to international guidelines. Fixed-dose combinations of ICS/LABA are commonly prescribed for both conditions, with fluticasone propionate (FP) and salmeterol forming a cornerstone of many treatment plans. An oral inhalation powder containing the combination of FP and salmeterol has been available as Advair Diskus® in the United States for almost 20 years, and the first and only substitutable generic version of this product has recently been approved for use: Wixela™ Inhub™. Bioequivalence of Wixela Inhub and Advair Diskus has been established. Furthermore, the Inhub inhaler was shown to be robust and easy to use, suggesting that Wixela Inhub may provide an alternative option to Advair Diskus for patients with asthma or COPD requiring intervention with an ICS/LABA.

Pharmacokinetic profile analyses for inhaled drugs in humans using the lung delivery and disposition model

The kinetic clarification of lung disposition for inhaled drugs in humans via pharmacokinetic (PK) modeling aids in their development and regulation for systemic and local delivery, but remains challenging due to its multiplex nature. This study exercised our lung delivery and disposition kinetic model to derive the kinetic descriptors for the lung disposition of four drugs [calcitonin, tobramycin, ciprofloxacin and fluticasone propionate (FP)] inhaled via different inhalers from the published PK profile data. With the drug dose delivered to the lung (DTL) estimated from the corresponding γ-scintigraphy or in vivo predictive cascade impactor data, the model-based curve-fitting and statistical moment analyses derived the rate constants of lung absorption (k_a ) and non-absorptive disposition (k_nad ). The k_a values differed substantially between the drugs (0.05-1.00 h^-1 ), but conformed to the lung partition-based membrane diffusion except for FP, and were inhaler/delivery/deposition-independent. The k_nad values also varied widely (0.03-2.32 h^-1 ), yet appeared to be explained by the presence or absence of non-absorptive disposition in the lung via mucociliary clearance, local tissue degradation, binding/sequestration and/or phagocytosis, and to be sensitive to differences in lung deposition. For FP, its k_a value of 0.2 h^-1 was unusually low, suggesting solubility/dissolution-limited slow lung absorption, but was comparable between two inhaler products. Thus, the difference in the PK profile was attributed to differences in the DTL and the k_nad value, the latter likely originating from different aerosol sizes and regional deposition in the lung. Overall, this empirical, rather simpler model-based analysis provided a quantitative kinetic understanding of lung absorption and non-absorptive disposition for four inhaled drugs from PK profiles in humans.

Biological Obstacles for Identifying In Vitro-In Vivo Correlations of Orally Inhaled Formulations

Oral inhalation of drugs is the classic therapy of obstructive lung diseases. In contrast to the oral route, the link between in vitro and in vivo findings is less well defined and predictive models and parameters for in vitro-in vivo correlations are missing. Frequently used in vitro models and problems in obtaining in vivo values to establish such models and to identify the action of formulations in vivo are discussed. It may be concluded that major obstacles to link in vitro parameters on in vivo action include lack of treatment adherence and incorrect use of inhalers by patients, variation in inhaler performance, changes by humidity, uncertainties about lung deposition, and difficulties to measure drug levels in epithelial lining fluid and tissue. Physiologically more relevant in vitro models, improvement in inhaler performance, and better techniques for in vivo measurements may help to better understand importance and interactions between individual in vitro parameters in pulmonary delivery.

Drug Concentration Asymmetry in Tissues and Plasma for Small Molecule-Related Therapeutic Modalities

The well accepted "free drug hypothesis" for small-molecule drugs assumes that only the free (unbound) drug concentration at the therapeutic target can elicit a pharmacologic effect. Unbound (free) drug concentrations in plasma are readily measurable and are often used as surrogates for the drug concentrations at the site of pharmacologic action in pharmacokinetic-pharmacodynamic analysis and clinical dose projection in drug discovery. Furthermore, for permeable compounds at pharmacokinetic steady state, the free drug concentration in tissue is likely a close approximation of that in plasma; however, several factors can create and maintain disequilibrium between the free drug concentration in plasma and tissue, leading to free drug concentration asymmetry. These factors include drug uptake and extrusion mechanisms involving the uptake and efflux drug transporters, intracellular biotransformation of prodrugs, membrane receptor-mediated uptake of antibody-drug conjugates, pH gradients, unique distribution properties (covalent binders, nanoparticles), and local drug delivery (e.g., inhalation). The impact of these factors on the free drug concentrations in tissues can be represented by K _p,uu, the ratio of free drug concentration between tissue and plasma at steady state. This review focuses on situations in which free drug concentrations in tissues may differ from those in plasma (e.g., K _p,uu > or <1) and discusses the limitations of the surrogate approach of using plasma-free drug concentration to predict free drug concentrations in tissue. This is an important consideration for novel therapeutic modalities since systemic exposure as a driver of pharmacologic effects may provide limited value in guiding compound optimization, selection, and advancement. Ultimately, a deeper understanding of the relationship between free drug concentrations in plasma and tissues is needed.

Overview of Brazilian Requirements for Therapeutic Equivalence of Orally Inhaled and Nasal Drug Products

Brazil has established a framework for provision of generic pharmaceuticals including for orally inhaled and nasal drug products (OINDP) to its populace. This includes the development of guidelines or "resolutions" and normative instructions describing the Brazilian medicines agency's (Anvisa) expectations for demonstrating OINDP therapeutic equivalence. The Anvisa regulatory framework for OINDP therapeutic equivalence, challenges, and comparisons with the US Food and Drug Administration and European Medicines Agency approaches are assessed and discussed.

Pharmacokinetics and Tolerability of Budesonide/Glycopyrronium/Formoterol Fumarate Dihydrate and Glycopyrronium/Formoterol Fumarate Dihydrate Metered Dose Inhalers in Healthy Chinese Adults: A Randomized, Double-blind, Parallel-group Study

PURPOSE

The objective of this study was to assess pharmacokinetic (PK) and safety profiles of 2 fixed-dose combinations in development for the treatment of chronic obstructive pulmonary disease (COPD): budesonide/glycopyrronium/formoterol fumarate dihydrate metered-dose inhaler (BGF MDI; triple combination) and glycopyrronium/formoterol fumarate dihydrate (GFF MDI; dual combination). The PK and safety profiles of BGF MDI and GFF MDI were assessed for the first time in healthy Chinese adults after single and repeated (7-day) dosing.

METHODS

This Phase I, randomized, double-blind, parallel-group study was conducted at a single site in Shanghai, China. Male or female Chinese subjects, 18-45 years of age and in good general health, were randomized 1:1:1 to receive BGF MDI 320/14.4/10 μg, BGF MDI 160/14.4/10 μg, or GFF MDI 14.4/10 μg. PK parameters were assessed after a single dose (day 1) and at steady state (day 8), and included AUC_0-12, C_max, and T_max. Tolerability was assessed using physical examination findings, adverse events reporting, 12-lead ECG, vital signs, and clinical laboratory values.

FINDINGS

Ninety-six subjects (mean age, 25.6 years; 83.3% male) were randomized and received treatment. All randomized subjects were included in the safety and PK populations. After single and repeated dosing, budesonide AUC_0-12 and C_max were increased dose proportionally from BGF MDI 160/14.4/10 μg to BGF MDI 320/14.4/10 μg, respectively (single dose: AUC_0-12, 811.8 vs 1748 h · pg/mL; C_max, 224.3 vs 459.3 pg/mL; repeated dosing: AUC_0-12, 1250 vs 2510 h · pg/mL; C_max, 315.4 vs 626.4 pg/mL). After single and repeated dosing, glycopyrronium AUC_0-12 and C_max were similar across all treatments (single dose: AUC_0-12, 27.20-29.40 h · pg/mL; C_max, 4.884-5.674 pg/mL; repeated dosing: AUC_0-12, 69.49-77.08 h · pg/mL; C_max, 11.30-13.12 pg/mL) and formoterol (single dose: AUC_0-12, 46.49-53.58 h · pg/mL; C_max 9.651-10.62 pg/mL; repeated dosing: AUC_0-12, 81.94-85.32 h · pg/mL; C_max, 16.13-17.71 pg/mL), suggesting that the addition of budesonide did not appreciably alter the PK properties of GFF MDI. All treatment-emergent adverse events were mild in severity and rates were similar across groups (range, 50.0%-56.3%). There were no new or unexpected findings on tolerability.

IMPLICATIONS

Overall, all treatments were well tolerated and PK parameters were generally comparable to those previously reported in Western and Japanese healthy subjects, suggesting that the doses of BGF MDI and GFF MDI in development globally for COPD are also appropriate for Chinese patients with COPD. ClinicalTrials.gov identifier: NCT03075267.

Pharmacokinetics of Single and Repeat Doses of Fluticasone Furoate/Umeclidinium/Vilanterol in Healthy Chinese Adults

The pharmacokinetics (PK) and safety of single-inhaler fluticasone furoate/umeclidinium/vilanterol (FF/UMEC/VI) after single and repeat dosing in healthy Chinese adults were assessed. In this open-label study (NCT02837380), subjects received once-daily FF/UMEC/VI 100/62.5/25 µg on day 1 and repeat doses on days 2-7. PK parameters (days 1 and 7) included maximum observed concentration (C_max ) and area under the plasma concentration-time curve (AUC) from time zero (predose) to last time of quantifiable concentration (AUC_0-t ). Terminal phase half-life (t_½ ) on day 1 was estimated. The primary objective was to assess systemic exposure of FF 100 µg, UMEC 62.5 µg, and VI 25 µg following single-inhaler triple therapy on days 1 and 7. On day 1, geometric mean t_½ of UMEC and VI was 0.36 and 0.52 hours, respectively; t_½ of FF was not representative because of nonquantifiable concentration data. On days 1 and 7, geometric mean C_max of FF was 10.46 and 27.32 pg/mL, respectively; C_max of UMEC was 144.14 and 241.35 pg/mL, respectively; and C_max of VI was 120.42 and 196.78 pg/mL, respectively. AUC_0-t of FF was 1.77 and 276.96 pg·h/mL, respectively; AUC_0-t of UMEC was 28.44 and 117.19 pg·h/mL, respectively; and AUC_0-t of VI, 42.46 and 101.12 pg·h/mL, respectively. The PK of FF/UMEC/VI was as expected for the individual-component PK previously reported in healthy Chinese adults. No new safety signals were observed.

On the pharmacokinetics of two inhaled budesonide/formoterol combinations in asthma patients using modeling approaches

Dry powder inhalers containing the budesonide/formoterol combination have currently a well-established position among other inhaled products. Even though their efficacy mainly depends on the local concentrations of the drug they deliver within the lungs, their safety profile is directly related to their total systemic exposure. The aim of the present investigation was to explore the absorption and disposition kinetics of the budesonide/formoterol combination delivered via two different dry powder inhalers in asthma patients. Plasma concentration-time data were obtained from a single-dose, crossover bioequivalence study in asthma patients. Non-compartmental and population compartmental approaches were applied to the available datasets. The non-compartmental analysis allowed for an initial characterization of the primary pharmacokinetic (PK) parameters of the two inhaled drugs and subsequently the bioequivalence assessment of the two different dry powder inhalers. The population pharmacokinetic analysis further explored the complex absorption and disposition characteristics of the two drugs. In case of inhaled FOR, a five-compartment PK model including an enterohepatic re-circulation process was developed. For inhaled BUD, the incorporation of two parallel first-order absorption rate constants (fast and slow) for lung absorption in a two-compartment PK model emphasized the importance of pulmonary anatomical features and underlying physiological processes during model development. The role of potential covariates on the variability of the PK parameters was also investigated.

Pharmacokinetic analysis of inhaled salmeterol in asthma patients: Evidence from two dry powder inhalers

Salmeterol (SAL) is a long-acting β2-adrenergic agonist, which is widely used in the therapy of asthma. The aim of this study was to investigate the pharmacokinetics (PK) of inhaled salmeterol in asthma patients using two different dry powder inhalers. This analysis was based on data from 45 subjects who participated in a two-sequence, four-period crossover bioequivalence (BE) study after single administration of the test (T) and reference (R) products. In order to mimic more closely the real treatment conditions, activated charcoal was not co-administered. Plasma concentration-time (C-t) data were initially analysed using classic non-compartmental PK approaches, while the main objective of the study was to apply population PK modeling. The relative fraction of the dose absorbed via the lungs (R_L ) was set as a parameter in the structural model. The plasma C-t profiles of salmeterol showed a biphasic time course indicating a parallel pulmonary and gastrointestinal (GI) absorption. A two-compartment disposition model with first order absorption from the GI and very rapid absorption from lungs (like an i.v. bolus) was found to describe successfully the C-t profiles of salmeterol. The estimated R_L value was 13% suggesting a high gut deposition of inhaled salmeterol. Women were found to exert less capability to eliminate salmeterol than men, while body weight (in allometric form) was found to be an important covariate on the peripheral volume of distribution.

Bronchopulmonary pharmacokinetics of (R)-salbutamol and (S)-salbutamol enantiomers in pulmonary epithelial lining fluid and lung tissue of horses

AIMS

Salbutamol is usually administered as a racemic mixture but little is known about the enantioselectivity of salbutamol pharmacokinetics in the lung. This study was designed to investigate enantiomer concentrations in lung tissue after inhaled dosing.

METHODS

Horses (n = 12) received racemic salbutamol 1000 μg via inhalation. Enantioselective ultra performance liquid chromatography-tandem mass spectrometry was used to determine salbutamol concentrations in pulmonary epithelial lining fluid (PELF) sampled 2, 5, 10 and 15 min after administration, in central lung (endoscopic bronchial biopsy) and peripheral lung (percutaneous pulmonary biopsy) tissues (at 20 and 25 min respectively), and in plasma samples.

RESULTS

Mean ± 95% confidence interval (CI) yield of PELF was 57 ± 10 mg. Initial mean ± 95%CI (R)- and (S)-salbutamol PELF concentrations were 389 ± 189 ng g^-1 and 378 ± 177 ng g^-1 respectively, and both reduced approximately 50% by 15 min. Mean ± 95%CI central lung levels of drug were higher than peripheral lung tissue for both (R)-salbutamol (875 ± 945 vs. 49.5 ± 12 ng g^-1 ) and (S)-salbutamol (877 ± 955 vs. 50.9 ± 12 ng g^-1 ) respectively. There was no evidence of enantioselectivity in PELF or central lung but minor (~2%) enantioselectivity was observed in the peripheral lung. Enantioselectivity was clearly evident in plasma with (S):(R) ratio of 1.25 and 1.14 for both area under the concentration-time curve (0-25 min) and C_max respectively.

CONCLUSIONS

PELF sampling in horses offers sufficient yield allowing direct detection of drug and, combined with tissue sampling, is a valuable model to investigate bronchopulmonary pharmacokinetics. Salbutamol did not demonstrate enantioselectivity in PELF or central lung tissue uptake following acute dosing, however, enantioselective plasma concentrations were demonstrated, with minor enantioselectivity in the peripheral lung.

Between-Batch Pharmacokinetic Variability Inflates Type I Error Rate in Conventional Bioequivalence Trials: A Randomized Advair Diskus Clinical Trial

We previously demonstrated pharmacokinetic differences among manufacturing batches of a US Food and Drug Administration (FDA)-approved dry powder inhalation product (Advair Diskus 100/50) large enough to establish between-batch bio-inequivalence. Here, we provide independent confirmation of pharmacokinetic bio-inequivalence among Advair Diskus 100/50 batches, and quantify residual and between-batch variance component magnitudes. These variance estimates are used to consider the type I error rate of the FDA's current two-way crossover design recommendation. When between-batch pharmacokinetic variability is substantial, the conventional two-way crossover design cannot accomplish the objectives of FDA's statistical bioequivalence test (i.e., cannot accurately estimate the test/reference ratio and associated confidence interval). The two-way crossover, which ignores between-batch pharmacokinetic variability, yields an artificially narrow confidence interval on the product comparison. The unavoidable consequence is type I error rate inflation, to ∼25%, when between-batch pharmacokinetic variability is nonzero. This risk of a false bioequivalence conclusion is substantially higher than asserted by regulators as acceptable consumer risk (5%).

Batch-to-batch pharmacokinetic variability confounds current bioequivalence regulations: A dry powder inhaler randomized clinical trial

Current pharmacokinetic (PK) bioequivalence guidelines do not account for batch‐to‐batch variability in study design or analysis. Here we evaluate the magnitude of batch‐to‐batch PK variability for Advair Diskus 100/50. Single doses of fluticasone propionate and salmeterol combinations were administered by oral inhalation to healthy subjects in a randomized clinical crossover study comparing three different batches purchased from the market, with one batch replicated across two treatment periods. All pairwise comparisons between different batches failed the PK bioequivalence statistical test, demonstrating substantial PK differences between batches that were large enough to demonstrate bio‐inequivalence in some cases. In contrast, between‐replicate PK bioequivalence was demonstrated for the replicated batch. Between‐batch variance was ∼40–70% of the estimated residual error. This large additional source of variability necessitates re‐evaluation of bioequivalence assessment criteria to yield a result that is both generalizable and consistent with the principles of type I and type II error rate control.

Current Scientific and Regulatory Approaches for Development of Orally Inhaled and Nasal Drug Products: Overview of the IPAC-RS/University of Florida Orlando Inhalation Conference

This article summarizes discussions at the March 2014 conference organized by the University of Florida (UF) and International Pharmaceutical Aerosol Consortium on Regulation and Science (IPAC-RS), entitled "Orlando Inhalation Conference: Approaches in International Regulation." The special focus of the conference was on global scientific and regulatory issues associated with the testing and demonstration of equivalence for the registration of orally inhaled drug products (OIDPs) in the United States, Europe, Brazil, China, and India. The scope included all types of OIDPs throughout their lifecycle, e.g., innovator/brand-name products, generics, modifications due to lifecycle management, device changes, etc. Details were presented for the U.S. "weight of evidence approach" for registration of generic products (which includes demonstration of in vitro and in vivo equivalence, as well as quantitative and qualitative sameness, and device similarity). The European "stepwise" approach was elucidated, and the thinking of regulatory agencies in the major emerging markets was clarified. The conference also highlighted a number of areas that would benefit from further research and discussion, especially around patient/device interface and human factor studies, statistical methods and criteria for demonstrating equivalence, the relative roles of in vivo and in vitro tests, and appropriate designs and metrics for in vivo studies of inhaled drugs.