This article is part of PharmTech's supplement "Solid Dosage and Excipients 2010."
Since the concept of quality by design (QbD) emerged nearly a decade ago, the pharmaceutical industry has been trying to understand and put into practice a more flexible and risk-based approach to manufacturing. Although the introduction of US Food and Drug Administration guidances and International Conference on Harmonization (ICH) guidelines—ICH Q 8, 9, and 10—have provided some details on how QbD can be applied, many questions remain. The development and use of excipients in drug-product formulations has posed several challenges, including understanding excipient variability and functionality when implementing a QbD-based approach.
To provide some answers and potential solutions to these common challenges, Pharmaceutical Technology gained input from the following industry experts: William F. Busch of Dow Wolff Cellulosics–Pharmaceutical Excipients, a business unit of Dow Chemical (Midland, MI), with Tom Frazier, product market manager for Carbowax Sentry, a product line of Dow Chemical; Stuart Porter, senior director of pharmaceutical research and development at International Specialty Products (ISP) in Wayne, NJ; and John Langridge, manager of research and development/quality control at DMV-Fonterrra Excipients (DFE) in Goch, Germany. They provide examples and advice on excipient selection, regulatory expectations, supply-chain considerations, and more.Excipient selection
PharmTech: Can you outline how QbD may be applied in excipient selection and understanding the functionality of the excipient in the formulation?
QbD comprises many steps that typically involve the following:
Ultimately, when this process is established, the goal is to minimize reliance on conventional in-process and post-manufacturing quality-control testing of samples by implementing an effective process-analytical-technology (PAT) strategy that enables critical process parameters (CPPs) to be monitored. This process uses tools that have feed-back and feed-forward capabilities, so that operation within the required design space is assured.
In terms of how QbD implementation might affect excipient selection, there are two key considerations. First, during the application of statistical DoE, it is likely that the impact (in quantitative and functionality terms) of the excipient will be determined. As a result of this analysis, selection of a particular excipient may well rest on how sensitive the formulation (and the ultimate manufacturing process) is to potential variation in that excipient. Such sensitivity should be considered in terms of the range of excipient content that can be tolerated without having a demonstrably negative effect on the formulation, and in terms of the likely impact of batch-to-batch variability in that excipient. Potential negative effects should be considered with regard to how the excipient affects functionality of the dosage form (e.g., drug-release characteristics) as well as the chemical stability of the active pharmaceutical ingredient (API) in the dosage form.
Second, during the risk-assessment stage, excipient selection may hinge on the size of that excipient's risk factor. For an excipient supplier, complying with the demands of a pharmaceutical manufacturer during this processes can be troublesome. The reason for this is that a pharmaceutical manufacturer will often ask for samples of a particular excipient that represent the extremes of the specification range. Although an excipient supplier will, out of necessity, set a range of specifications for a particular material, that material is often manufactured to tolerances that are much tighter than those depicted by the specification ranges. Production processes are then designed to target the middle of that range to avoid out-of specification production. Hence, it may not be possible to supply samples that represent the extremes of the specification ranges.
Langridge (DFE): We see an increasing trend in customers' application of QbD to excipients. In terms of excipient selection, there is more interest in matching excipients to processes in addition to traditional excipient selection using preformulation and excipient compatibility studies. Examples include selection of materials with good recompacting properties for dry-granulation processes (e.g., roller compaction) and selection of materials with low sensitivity to lubricants and to compaction speed for scale-up.
With regard to understanding functionality, there is a definite trend in testing the ranges of excipient specifications during the development process. This, of course, depends on the criticality of the excipient for correct performance. Although not directly relevant to oral solid dosage forms, QbD studies are always applied to carrier lactose for dry-powder inhalers, to the extent that several customers now frequently request commercial batches, not just trial batches, targeted to a particular point in the overall particle-size specification.
Additionally, we see more interest in the understanding of how nonspecified properties (i.e., not specified on a certificate of analysis, or CoA) of an excipient may affect processing. One example is the role of amorphous lactose in the compaction of spray-dried lactose, and the proper packaging and environmental controls needed to maintain the amorphous lactose. Another example is the role of viscosity of polymeric disintegrants and the effect of viscosity on granulation and disintegration.