Factors Influencing the Dispersibility of Glycopyrronium Bromide and Indacaterol Maleate – Combined In Vitro and In Silico Study

Abstract

The development of dry powder inhalers (DPIs) for pulmonary drug delivery is complex, requiring optimization of variable factors to ensure effective lung deposition. This study investigates the factors influencing the dispersibility of glycopyrronium bromide (GLP) and indacaterol maleate (IND) in adhesive mixtures using both in vitro and in silico approaches. The formulation was designed to match the reference listed drug (RLD), using lactose and magnesium stearate as excipients. Key variables examined included mixing energy, carrier particle size distribution (PSD), and active pharmaceutical ingredient (API) particle size characteristics across multiple suppliers.

A Next Generation Impactor (NGI) was employed to assess the aerodynamic particle size distribution (APSD) of 67 formulations. The collected impactor data were analyzed using machine learning (ML) models, leveraging the h2o AutoML framework. Stacked ensemble models demonstrated high predictive accuracy (R²: 0.940 for GLP, 0.969 for IND), identifying key formulation parameters affecting dispersibility. SHAP analysis revealed that GLP dispersibility was influenced primarily by GLP PSD (d90, d50, SPAN), lactose d10, and mixing energy, while IND was more dependent on lactose PSD and its own particle size.

The findings confirm that both APIs interact with each other within the formulation, significantly impacting their reciprocal deposition profiles. These insights highlight the challenge of developing bioequivalent DPI formulations and emphasize the importance of PSD control, mixing energy optimization, and advanced ML modeling in predicting therapeutic equivalence. The study provides a predictive framework to support the development of generic inhalation products, improving regulatory approval pathways and ensuring effective pulmonary drug delivery.

Introduction

Generic drugs offer substantial cost savings for both consumers and healthcare systems. However, while generics are widely available for many medications, the approval and adoption of generic orally inhaled drug products (OIDPs) have been retarded due to the complexities involved in their development and market release. The performance of OIDPs depends on multiple factors, including formulation properties, targeted lung delivery, device functionality, and patient adherence, making their generic versions challenging to replicate and approve (1). The OIDPs may appear to be simple formulations at first glance, but their development is a complex and demanding process (2, 3).

Dry powders for pulmonary drug delivery are referred to as adhesive mixtures. This term embraces the thermodynamic changes occurring during the mixing process of finer active pharmaceutical ingredient (API) particles with coarser carrier particles (4, 5). In adhesive mixtures, lactose monohydrate remains the most widely recognized and used carrier (2). In some compositions, a ternary component such as magnesium stearate (MgSt) is used to optimize the mixture’s properties and adjust interparticulate forces for better aerosolization (7,8,9). In our study, to align with the reference listed drug (RLD) formulation, lactose and MgSt were selected as excipients.

In the development of inhaled adhesive mixtures, achieving suitable dispersibility remains the key objective, along with ensuring mixture homogeneity and stability (10). In vitro dispersibility is measured by the Next Generation Impactor (NGI). This analysis provides the aerodynamic particle size distribution (APSD) across the stages and alongside the fine particle fraction (FPF – the fraction that can reach the lungs) enabling the characterization of the drug deposition pattern in the lungs (11). In generic product development, comparing APSD and the target delivered dose between the proposed generic product and the RLD is crucial for demonstrating therapeutic bioequivalence (12, 13).

The literature recognizes numerous variables that affect the performance of adhesive mixtures for inhalation, including the mixing process, the properties of raw materials, and magnesium stearate content (14, 15).

The mixing process directly influences content uniformity and aerodynamic properties of inhaled mixtures (16, 17). While content uniformity is a well-recognized area, the effects of blender type, mixing time and mixing speed on the interparticulate drug-to-carrier forces formed during the mixing process, and consequently on the dispersibility of the adhesive mixture, remain not fully recognized (10). Recent advancements in the development of adhesive mixtures for pulmonary drug delivery emphasize the crucial role of mixing energy in controlling formulation performance (16, 18). This approach, applied in the high-shear mixing process, describes numerically the dependence of mixing time, mixing speed and the characteristics of the carrier used. The mixing energy concept has proven to be a critical tool for adjusting aerodynamic performance without altering the drug composition, as demonstrated in adhesive mixtures containing glycopyrronium bromide (GLP) and indacaterol maleate (IND) (11).

The particle size and morphology of lactose and APIs are physicochemical properties that directly influence the delivery of dry powders to the lungs (20,21,22). Only particles with an aerodynamic diameter in the range of 1- 5 µm can reach the lower respiratory tract and have adequate cohesiveness for optimal dispersion (6, 23, 24). The size of raw materials used in dry powders for inhalation is described by the PSD with parameters such as d10, d50, d90, SPAN or the percentage of particles smaller than, for instance, 10 µm. Also, the shape and surface of particles affect interparticulate interactions and therefore their adhesiveness/cohesiveness and dispersibility (22, 25). While these variables are widely recognized, the performance of adhesive mixtures depends on their interactions, adding complexity to the matter (26).

The primary aim of this study was to develop a predictive model for aerosol performance to support formulation optimization and facilitate the regulatory approval of generic inhalation products. To achieve this, we investigated the key variables influencing the deposition of GLP and IND, with a focus on mixing energy as the main experimental factor. Variability in lactose properties was addressed by including multiple suppliers and grades, with particle size distribution assessed as a secondary variable. Formulations were prepared and analyzed for APSD using a Next Generation Impactor (NGI). Machine learning techniques were applied to the collected data to identify the factors affecting dispersibility and to understand the influence of each variable on the aerosolization behavior of the active pharmaceutical ingredients (APIs). The study also explored potential interactions between GLP and IND and how these might affect overall formulation performance, aiming to establish an optimal formulation strategy to ensure therapeutic equivalence.

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Materials

Micronized glycopyrronium bromide was purchased from three suppliers: Melody Healthcare (Mumbai, India), Hovione Limited (Loures, Portugal), and INKE (Barcelona, Spain). Micronized indacaterol maleate was sourced from four different suppliers: Chemo Industriale Chimica (Saronno, Italy), Melody Healthcare (Mumbai, India), Neuland Laboratories Ltd. (Bonthapally, India), and INKE (Barcelona, Spain). Various grades of active pharmaceutical ingredients (APIs) were tested from each supplier. Additionally, non-micronized glycopyrronium bromide from Melody Healthcare (Mumbai, India), with an initial crystal size range of 500–1500 µm, was jet-milled in-house using a Fluid Jet-Mill J-20 (Tecnologia Meccanica, Italy). The material was manually fed into the cylindrical milling chamber through a venturi system using pressurized air. Milling was performed at pressures of 2.0, 3.0, 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5 bar. The micronized material was then conditioned for 24 h and stored in antistatic polyethylene bags for subsequent analysis and storage.

Lactose monohydrate was supplied by DFE Pharma (Goch, Germany), while MgSt LIGAMED MF-2-V-BI, used as a force control agent, was sourced from Peter Greven GmbH & Co. KG (Bad Münstereifel, Germany).

Rzewińska, A., Szlęk, J., Juszczyk, E. et al. Factors Influencing the Dispersibility of Glycopyrronium Bromide and Indacaterol Maleate – Combined In Vitro and In Silico Study. AAPS PharmSciTech 26, 230 (2025). https://doi.org/10.1208/s12249-025-03182-9