A follow-up post from LinkedIn Discussion Forum for the visitors of this blog.
With reference to your comment, “Our consensus starting point is that a scientific definition of a quality attribute (we will focus here on rate and extent of drug dissolution) is necessary for QbD. “
For simplicity and clarity sake, I would consider the “quality attribute” in two parts: (1) quality – establishing the patient’s need which is fulfilled by the product (2) attribute – a measurable characteristic that would reflect the quality aspect. For the purpose of our discussion, quality means – a product must deliver the drug as expected (which consumer needs). Note a subtle difference here, but a critical one, that the consumer does not need a product but a drug; however, buys a product to fulfill the need for the drug. So, the quality of a drug product becomes its ability to provide the drug to the patient in an expected manner. As a scientist, we need to acknowledge and fulfill this need of the patient. To answer this question scientifically, we need to define a measurable characteristic of the product showing the deliverability of the drug – this measurable characteristic becomes the quality attribute of the product. In general terms, this quality attribute is known as the product’s drug release/delivery capability. So, in reality, drug release/delivery capability is the quality attribute. Measurement of the quality attribute will depend on the product type, most likely depending on the product’s route of administration. For our current discussion, we will initially start or restrict our discussion to oral products such as tablets and capsules. For oral products, drug release capability (quality attribute) is measured by the drug dissolution characteristics of the product in the GI tract. As drug dissolution is a critical characteristic for assessing oral product drug release/deliverability, it becomes CQA. Please note here that drug dissolution test/testing is not a quality attribute but a test to measure the quality attribute (drug release capability) of the oral products. So, if one likes to move towards QbD, one needs to agree on the terminology of quality and its attribute, followed by its measuring approach. Let me know your views on this aspect, and then we will move further.