In the drug dissolution testing area, a reference to the “quality” of a product (table/capsule) is frequently made. For example, a drug dissolution test may be considered a quality assurance and/or control test. More recently use of the term has been extended to the concept and practice of “quality by design” or QbD. Obviously, to achieve or monitor “quality,” one needs to define it as an achievable objective or goal.
In general terms, “quality” is a subjective term for which each person or sector has its own definition. For example, certain variations in shape, size, or color of a tablet may indicate poor quality of the product for some, but for others, it may be normal and expected. In the literature, commonly, “quality” refers to “fitness for use” or “conformance to requirements” according to Joseph Juran (considered father of the QbD concept) and Philip Crosby, respectively. However, in technical usages, such as for the assessment of pharmaceutical products, these definitions of “quality” may be translated into a product property that fulfills stated or implied needs by establishing it as “fit for use.” The terminology “to fulfill stated or implied needs” appears to be the most critical in this regard, i.e, one must establish the need before defining the quality.
Therefore, before using dissolution testing for “quality” assessment purposes (or its control/assurance), one must first describe the stated or implied need here. Until and unless one cannot define or establish a need or use (for the testing) one cannot establish the quality. What is the need or use of a drug dissolution test? Conducting a dissolution test is not a need by itself. However, it is the ability (test) to fulfill a need of determining drug dissolution in the human GI tract from pharmaceutical products. The need is to determine drug dissolution in the human GI tract. This particular needed characteristic reflects upon the “quality” of the product. How it is to be determined and controlled or assured comes later, which is the “fitness for use” characteristics. In this regard, both, i.e., bioavailability/bioequivalence (BA/BE) testing/studies and drug dissolution testing, are two different types of tests to fulfill the same need and to establish “fitness for use” criteria. One reflects the in vivo evaluation while the other in vitro, but they both fulfill exactly the same need. One may argue about the differences in the strength of these two types of tests, but one has to recognize that they both fulfill the same need. Once the need is established, then one has to establish a tolerance (specifications) for “fitness to use” around the needed characteristics so that this need may be fulfilled consistently. For further discussion on the evaluation of drug release (dissolution) characteristics for both in vitro and in vivo, please see the post.
In short, therefore, “quality” here is referred to as fulfilling a need of determining the drug release (dissolution) from a product in the gastrointestinal (GI) tract, which is quantitatively measured to establish the “fitness for use” by a drug dissolution test