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Putting the Quality into Quality by Design- By Jeff Duke

People working in the Pharmaceutical Industry are often puzzled by the lack of clear guidance on how to practice Quality by Design (QbD). The ICH guidelines from Q8(R2) onwards do not provide definitive how-to guides; rather they discuss concepts and tools. They are therefore rather different to the guidances from Q1-7 which were more contractual in nature. One of the keys to understanding this change is to recognise how the definition of Quality has changed from the earlier guidelines to the later ones. Here is the definition of Quality from ICH Q6A

…The suitability of either a drug substance or drug product for its intended use. This term includes such attributes as the identity, strength, and purity.

We can immediately see that such a definition is strongly linked to the specification of the material. In other words, if the material met specification it was, by definition, a quality product.

Now let’s look at the definition of Quality from ICH Q9

…The degree to which a set of inherent properties of a product, system or process fulfills requirements

And these “Requirements” are defined as:

…The explicit or implicit needs or expectations of the patients or their surrogates (e.g., health care professionals, regulators and legislators). In this document, “requirements” refers not only to statutory, legislative, or regulatory requirements, but also to such needs and expectations.

It is very clear that this definition, with its discussion of concepts such as implicit needs and expectations cannot be neatly encapsulated in a specification. However, the practice of QbD utilises another document designed to list all of the requirements of a drug product as defined above so that they can be used to guide the development of a product that fulfils them – a quality product. This document is the Quality Target Product Profile (QTPP) and it is a very different document to a specification. Producing a QTPP that really does encompass all product requirements takes effort and a multidisciplinary approach. Once a QTPP has been developed to its first iteration, it becomes a powerful tool to guide the development of a quality product.