Current Approaches to Design Space Development and Regulatory Applications for Drug Products: Findings from the IQ Utilization of Design Space for Filings Working Group Survey.

PURPOSE: The concept of a Design Space (DSp) was introduced in ICH Q8 as a tool within the quality-by-design (QbD) approach to pharmaceutical development with the intent of being globally applicable. However, there appears to be variance in the regulatory agency expectations in pharmaceutical product filing and implementation of DSp. This paper presents some of the current industry perspective on design space. METHODS: The Utilization of Design Space for Filings (UDSpF) Working Group in the Innovation and Quality (IQ) Consortium conducted a survey to establish a baseline for the current understanding of DSp among IQ member companies and assess the similarities and/or differences in strategies when filing a DSp. The survey focused on how IQ member companies approach DSp development, the primary drivers for the DSp, the presentation of the DSp in the filing, DSp verification and the benefits and flexibility anticipated and/or realized. RESULTS: A total of 14 responses were received and analyzed representing a small sample size but a large proportion of the innovator industry/large pharmaceutical companies. The survey results revealed that DSp is not yet a commonplace for small molecule drug products and may not even be utilized as much in large molecule drug products. The benefits of DSp, with respect to enhanced process understanding, are well understood by the sponsors; however, the benefits of filed DSp with respect to manufacturing flexibility are not fully realized in the commercial lifecycle of the product. There are also challenges in gaining consistent buy-in/value proposition for DSp among cross-functional teams within organizations. CONCLUSIONS: There are still gaps in design space implementation for its full benefit in the pharmaceutical industry. The WG has presented a unified view from member companies on the approach to DSp considering when/where the DSp experiments are conducted and on the extent of the DSp development proposed in a dossier.

Preparation of sustained release matrix pellets by melt agglomeration in the fluidized bed: influence of formulation variables and modelling of agglomerate growth.

The one-step preparation of sustained release matrix pellets, using a melting procedure in a fluidized bed apparatus, was tested in a 2(3) full factorial design of experiments, using microcrystalline wax as lipophilic binder, theophylline as model drug and talc as additional matrix forming agent. The three influence parameters were (A) size of binder particles, (B) fraction of theophylline in solid particles and (C) fraction of microcrystalline wax in formulation. The response variables were agglomerate size and size distribution, dissolution time, agglomerate crush resistance, sphericity, yield and porosity. Nearly spherical pellets comprising a smooth, closed surface could be obtained with the used method, exhibiting the hollow core typical for the immersion and layering mechanism. The reproducibility was very good concerning all responses. The size of agglomerates is proportional to the size of the binder particles, which serve as cores for pellet formation in the molten state in the fluidized bed. Additionally, the agglomerate size is influenced by the volume of the solid particles in relation to the binder particles, with more solid particles leading to larger agglomerates and vice versa. Dissolution times vary in a very wide range, resulting from the interplay between amount of drug in relation to the meltable matrix substance microcrystalline wax and the non-meltable matrix substance talc. The change of binder particle size does not lead to a structural change of the matrix; both dissolution times and porosity are not significantly altered. Agglomerate crush resistance is low due to the hollow core of the pellets. However, it is significantly increased if the volume fraction of microcrystalline wax in the matrix is high, which means that the matrix is mechanically better stabilized. A theoretical model has been established to quantitatively explain agglomerate growth and very good accordance of the full particle size distributions between predicted and actual values could be shown. A low volumetric binder to solids ratio is compensated by a more porous layer. On the basis of this model, in-depth understanding on the mechanism and influence of product properties could be gained; and an a priori estimation of particle size distributions for new formulas can be performed, with densities, formula, and binder particle size distribution as input parameters.