It is often suggested that to obtain appropriate dissolution characteristics of a product one may use or select an apparatus depending on the product attributes and/or desired release characteristics such as discriminating profiles, reproducibility, bio-relevancy etc. Such reasoning however, dictates that the analyst/formulator should have an idea about the expected outcome of the results, whether based on an educated guess or from prior experimentation. By selecting a particular apparatus and/or its associated experimental conditions, one is in fact trying to achieve the results reflecting one’s own expectation.
For example, when one conducts an experiment using the paddle apparatus and finds dissolution results of a tablet product, and their variability, higher than expected while observing that some, or all, tablets are floating within the vessel during testing. Such behavior or experiment is commonly considered flawed or inappropriate. A common practice to rectify this “problem” is to either use the basket apparatus, or a sinker, to restrict this floating behavior assuming that this may be causing the higher results and variability. This means that the analyst/formulator already has a preconceived idea/expectation about the results and variability of the product, and is trying to obtain those results by adjusting the means, in this case by using a different apparatus or a sinker. Obviously, the analyst is not determining dissolution characteristics of the product but achieving intended results by adjusting tester and/or associated experimental conditions.
Another similar common practice is that if a dissolution test is conducted using paddle or basket at 50 rpm and the percent drug dissolution is lower or slower than expected, then it is considered legitimate to raise the rpm to 75 or 100 rpm, to increase the rate and/or extent of the dissolution within a pre-set time period. Again, it clearly shows that the analyst/formulator has a preconceived dissolution characteristic of the product, which he/she is trying to achieve by adjusting the experimental conditions, in this case, rpm.
This is exactly the same situation, as if an analyst believes that weight of a tablet is “x” mg while the temperature of a water bath is “t” ºC so he/she searches for a certain balance or thermometer, or make adjustment to these, to achieve the desired and expected weight and temperature, respectively. Using this approach the analyst will not able to determine the true weight of the tablet and temperature of the water bath. The only way to know the true and accurate weight and temperature is to use balance and thermometer that are standardized and calibrated against some references and then used for measuring the weight of the tablets and temperature of the water bath. The outcome of balance and thermometer will be considered the weight of the tablet and temperature of the water bath. If these results are not as expected or desired then the analyst has to adjust the weight or temperature independently to achieve the desired, measured by the same calibrated balance and thermometer used before. Adjustments to the testers are not made.
Furthermore, one can also use a different type of balance or thermometer which may operate based on completely different operating principles. These different balance and thermometer should provide the same weight of the tablet and temperature of water bath. The reason being that both sets of devices (balances and thermometers) are measuring the same property/parameter of the tablet and water bath, therefore their outcome must be the same, if not then one or both balances and thermometers are considered to not be working properly.
Similarly, if one would require to measure dissolution characteristics of a product, no matter which type of tester one uses, they all must provide the same results. A product cannot have different types of dissolution characteristics at the same time. It is simply an illogical practice. However, at present, dissolution scientists have somehow gotten convinced, unfortunately falsely, that each and every type of tester would or should provide a different dissolution characteristics and the analyst chooses the one which provides the required outcome. It is just like different types of balances and thermometers providing different weights and temperatures and one just selects which fits the requirement or need. Obviously, this is inaccurate. Similarly obtaining and reporting different dissolution results of the same product using different apparatuses is simply incorrect. A product can and should have only one type of dissolution characteristics. If different apparatuses are providing different results then the use of such apparatuses should immediately be stopped. These apparatuses are not providing dissolution characteristics of the product but something else.
