In my opinion, current practices of method development have not only caused the biggest confusion in the industry but also hindered in an appropriate evaluation of drug products using dissolution (release) testing itself.
Current practices of method development suggest that an analyst is to “fish” (seek) experimental conditions, such as choice of an apparatus (paddle/basket), rpm, buffer, pH to establish UNKNOWN dissolution characteristics of a product. Commonly, it is suggested that an analyst have a number of formulations with presumed dissolution characteristics, and the analyst should seek experimental conditions that would reflect “presumed” product characteristics. Such practices are often referred to as developing “discriminating” and/or “lot-to-lot consistency check” methods.
Similarly, the above-mentioned practice of “fishing” (seeking) experimental conditions will be considered as developing a bio-relevant method if the analyst tries to match dissolution results with in vivo results (bioavailability/bioequivalence).
Therefore, in practice, an analyst would never know the true product dissolution characteristics but would select experimental conditions which would fit his/her expectations. It is, therefore, critical to understand that as it stands now, an analyst or a product developer will never know the true dissolution characteristics of its product. Each and every analyst/product developer is occupied with “developing” dissolution methods which in reality should not be their assignment. Their objective is to develop a product based on its dissolution characteristics, using a standardized and well-accepted dissolution method. This is similar to an analogy in which each and every laboratory would be busy developing their own thermometers and weighing balances to monitor temperatures and weighing substances, respectively.
Therefore, it is essential to note that the pharmaceutical industry requires a standard dissolution tester and its associated experimental conditions capable of providing dissolution characteristics of pharmaceutical products. The crescent-shaped spindle has been developed with these thoughts in mind, which appears to offer a powerful solution to the current confusion and avoids the unnecessary practices of method development.