BIOANALYTICX

These apparatuses:

1. Lack of scientific merit and support. Experimental studies have shown that they will provide highly variable and unpredictable results because of poor product/medium interaction.

2. Cannot be qualified/validated using commonly used industry-wide practices of qualifications for analytical instruments. In particular, they do not meet the requirements of design qualification (not fit for intended use) and operation qualification (cannot be qualified using a reference product).

3. Require meeting undefined and unqualified requirements such as de-aeration of the medium and control of vibration in and around the equipment.

4. Require drug and/or product-dependent experimental conditions. Therefore, it will not be possible to know whether dissolution characteristics reflect the products or the experimental conditions used.

5. Do not differentiate between IR and ER products. The analyst must first know what type of release/dissolution to expect from the product and then use the design of the experimental conditions to provide the presumed released/dissolution characteristics.

6. Are routinely used for evaluating drug products for human use (e.g., pharmacopeial testing). However, they have never been validated to demonstrate that they can provide bio- or physiologically relevant results.

7. Are often used for quality control and to check lot-to-lot consistency purposes. However, a link of these apparatuses, and associated experimental conditions, to the quality of a product, and consistency thereof, is unknown or undefined. The only criterion used for this purpose is that the dissolution results must meet some arbitrary standards/tolerances. If the criterion is not met, it is assumed that the products may be of substandard attributes.

8. Are expected to provide discriminatory tests which should be capable of showing formulation/manufacturing differences among products and/or batches. On the other hand, it is a well-known fact that these apparatuses frequently provide discriminatory results lacking any physiological significance or consequence.

9. Do not simulate in vivo or physiological environment (stirring and mixing) thus, one cannot develop bio-relevant tests.

10.   Require tolerances be set lower than potency and content uniformity values. Thus, results will reflect the inaccurate and inappropriate quality of perfectly acceptable products.

Considering the above-mentioned deficiencies, results obtained using these apparatuses can easily be questioned/challenged for their validity and relevance.

It is a fact and often a regulatory requirement that one has to demonstrate that an apparatus is capable of providing the intended and expected outcome. A simple and common example of this requirement is the calibration of a laboratory weighing scale or balance. Initially, when a balance is purchased, and then occasionally after that, it must be calibrated against reference weights to show that the balance can provide accurate weights of the references. If the balance does not perform as expected, then it has to be adjusted accordingly. please click here for the complete article

It is often asked which approach one should choose and why, i.e., is there a reason for the preference for one over the other?

Such a question has two components; (1) scientific or logical (2) required standards. Generally, the required standards component is based on the first one, i.e., science and logic. Unfortunately, in the case of the current practices of dissolution testing, scientific principles are entirely absent from the standardization. That is why there is so much difficulty, along with the associated frustrations.

I provide suggestions based on underlying scientific principles, which often do not fit well with the current practices because, as I stated above, the current practices lack scientific reasoning and logic. People say that both MQ and PVT are good and valid, which is correct, and an analyst can choose either. However, the next question is, which one is better and why. That is where the difficulty is. If one likes to know which one is better, then one has to know the reason behind conducting these tests, which will help decide and rationalize the preferred one.

So, the question is, why these MQ and PVT are done? The answer is to establish that the apparatuses fit their intended purpose, i.e., apparatuses can be used to evaluate the dissolution characteristics of a product for human use. The next question is, or at least should be, that if one meets the requirements of MQ/PVT, will the apparatuses be considered fit for evaluating the product for human use. The answer is no because both MQ/PVT lack the critical link between apparatuses and the evaluation of dissolution characteristics of a drug product (please use the link to read the article for further discussion). Therefore, in general, MQ and PVT are not useful practices and requirements and are unnecessary burdens on the pharmaceutical industry.

If the testing (MQ/PVT) lacks any real benefit, but has to be performed to meet the requirement, I would prefer the MQ. The MQ takes the responsibility away from the analysts and transfers it to the vendors of the dissolution testers. They can provide certification that the testers meet the specifications, which they usually provide when one purchases an apparatus and may provide later as well. In addition, the beauty of MQ is that no one can question that an apparatus does not work/perform as expected because there is no way to prove that it does not work, as the performance of the apparatuses is not associated with the MQ requirements. So, my dear analysts, go with the MQ and say goodbye to the PVT and its so-called “best practices”.

This article provides a discussion based on data presented in the literature that a direct comparison of dissolution results (profile) with blood levels (C-t profiles) can lead to misleading interpretation. For a more appropriate comparison, dissolution results should first be converted to C-t (plasma drug conc.-time) profiles. Examples are provided for converting dissolution profiles, using convolution techniques, to C-t profiles, which improve dissolution results evaluation. The article also presents an argument that for proper reflection of bio-relevancy of dissolution results, the tests require higher agitation (or product/medium interaction) relative to what is provided by the paddle apparatus at 50 and 75 rpm. please click here for the complete article

Predicting drug concentration-time (C-t) profiles in humans is highly desirable and needed for appropriate development of products and establishing their quality during production. Based on the convolution approach, a simple method to predict or estimate the C-t profiles has been suggested [link].

This article provides an application of the approach for the evaluation of metoprolol tartrate tablet products. Furthermore, it also demonstrates that the approach can be used to predict the C-t profiles for a sub-population as well. please click here for the complete post

A commonly asked question is how one should select a dissolution apparatus. It may be of interest to know that such a question is often asked when a dissolution analyst gets frustrated with the unexpected or unanticipated dissolution behavior of a test product. However, such a question is seldom asked at the beginning of the project as it is always understood or assumed that one will most likely use a paddle apparatus. Furthermore, the analyst will try some variations of rpm (50, 75, or 100) or medium (different buffers and pHs). If this does not work, the basket apparatus may be tried with similar variations in RPMs and buffers. In the end, the analyst usually settles on a test that will provide the anticipated/expected characteristics of the test product. Please click here for the complete post

It appears that there is confusion in the description of these terminologies. In reality, these are one and the same thing. Let me explain:

A bio-relevant dissolution test is a test, which should be able to differentiate (discriminate) between the in vivo behavior of two or more products. The in vivo behavior means bioequivalency or bio-in-equivalency of the tested products. Therefore, by its very nature, a bio-relevant test becomes a discriminatory test as well.

So, why are these two terminologies often referred to as different or separate? It is due to the fact that in the dissolution testing area, a discriminatory test is also described as, wrongly, an in vitro dissolution test, which may show formulation/manufacturing differences without their in vivo relevance or consequence. Such tests are often described as QC or consistency-check tests (e.g., in pharmacopeias). It is important to note that these tests do not relate to the in vivo characteristics of products. However, they are still expected to reflect quality of the products for humans uses. How? It is not clear and is the most confusing part of current dissolution practices! In my opinion, these tests (QC or in vitro discriminatory) and their requirements are not very useful and conducted as a “tradition”.

It is like developing a (“discriminatory”) thermometer which will show differences of a couple of degrees of temperature from person to person (or within a person) and then developing another (real/actual) thermometer which will reflect whether a person has a fever or not based on a difference in the temperature reading. In dissolution terminology, the first type of thermometer would be called a “discriminatory” test or tester and the second type as “bio-relevant.” Can anyone tell me why we should have the first type of thermometer or test?

The purpose of this explanation is, if possible, to avoid using the word/terminology of a “discriminatory” test, as it takes an analyst away from the objective of drug dissolution testing. The only test required is the one that should be bio-relevant.

For developing such a test, one first has to define what a bio-relevant test is. I have explained this in one of my earlier posts (see Link). Briefly, a bio-relevant test is a test that not only provides physiologically relevant results, but these results must be obtained using physiologically relevant experimental conditions. Trying experimental conditions without their physiological significance or relevance would not be a useful exercise.

One main consideration in this regard is that as human physiology remains the same, the experimental conditions should also remain the same. Therefore, working with different experimental conditions, particularly specific to your product, will violate the fundamental requirements of (bio-relevant) dissolution testing.

The physiological environment dictates the following single set of experimental conditions. (1) Temperature 37 °C (2) Medium: aqueous buffer having pH between 5 and 7 (use of water can be a good choice or start), with or without solubiliser (3) Mixer: To provide gentle but thorough stirring and mixing. That is it!

One does not have the option of trying different experimental conditions. It is very important to note that, if one deviates from this testing requirement, then that test may not be considered as a bio-relevant test, even if it provides matching bio results, as they are not obtained using bio-relevant experimental conditions.

Presently, paddle/basket apparatuses are used as mixers/stirrers, which have been shown to provide no or limited stirring and mixing. Therefore, one should NOT expect to obtain bio-relevant results using these apparatuses. If one obtains bio-relevant results using apparatuses, these should be considered as a match by chance.

Therefore, the first thing in trying to obtain bio-relevant results is to try a different stirring/mixing approach. There is no simple or practical option available, at least in my view, other than to try a different apparatus which shows gentle but thorough mixing and stirring environment.

Another important thing to consider is that one cannot develop a method using a product that is still under development (see link). One has to have a reference product with known drug dissolution characteristics which unfortunately is not available at present.

In the absence of such a reference product, one may consider developing a method based on an approach of relative dissolution testing (as explained here).

In short, therefore, one needs to develop a bio-relevant dissolution test which by default will be discriminatory. The choice of experimental conditions should be based on the physiological environment. The experimental conditions should be established using well-established products for human use and must not be based on a product that is under development.

As a starting point, the following may be considered: water as a medium (900 mL), with or without a solubilizer, maintained at 37 °C with a gentle but thorough stirring and mixing, perhaps using the crescent-shape spindle or another similar approach.

Links to two other articles which you may find helpful as well (article1, article2)

As described in one of my earlier posts, one can easily perform an analytical method validation by spiking the dissolution medium using a solution of a drug (API, link). The suggested approach is scientifically correct and valid. However, I do see where dissolution scientists, in general, will face difficulties. Let me explain:

Suppose an analyst follows the suggestion made and obtains a %RSD of “X” for the method (say less than 5) and the analyst is happy with it. Then, the analyst proceeds to the next step, test the tablets, and gets a %RSD of “Y”.  Under normal circumstances, this will reflect the %RSD of the product, including %RSD of the method. Usually, there are no concerns as this value of “Y” often comes out acceptable, between 5 and 10.

However, dissolution testing, particularly using paddle/basket, faces a unique problem, that it introduces one additional variability component, which is very well documented in the literature. This is because of the positioning effect of the tablet/capsule i.e., where it settles at the bottom of the vessel (link1, link2, link3). Unfortunately, people do not realize how such a minor variation can cause a big problem, but it does. As one cannot control this positioning effect, one cannot control variability due to this effect. It is totally random. The contribution from this random effect is reported to produce very high RSD, up to 37% (link). So, when it is asked what should be the expected variability for drug dissolution testing of a product, a safe bet/estimate is 37%. A product may have excellent repeatability/reproducibility of its drug dissolution characteristics (with extremely low %RSD). However, dissolution results may or may not reflect this low variability.

It is just like any other biased but random phenomenon, where one may or may not succeed. However, one always sees advertisements of some examples of big winnings/successes. In dissolution terminology, one may observe some low %RSD values at random, but overall variability using paddle/basket apparatuses will always be high. There are many publications available describing this high variability aspect, which may be useful. In addition, some posts may also be useful in this regard e.g., see link.

It is often noted that drug dissolution results fail to reflect the in vivo behavior of a product, i.e., lack of relationship to bioequivalence of two test products. Therefore, it is usually inquired as to how one should explain the lack of relevance and/or how to address this issue.

There could be a number of potential causes for such a problem (lack of bio-relevance). In addition, the problem could only be related to the specific product. In such cases, it is difficult for others to provide suggestions without knowing the details about the formulation of the product, which are often not available because of the proprietary nature of the information. Therefore, it is almost impossible that one can obtain a direct and/or a correct suggestion to address the problem. The formulator should be aware that he/she might obtain completely unrelated suggestions that may waste a lot of time. Keeping these thoughts in mind, a few very general suggestions are provided here, which may be helpful in such situations.

There are usually two potential outcomes in such situations (lack of bio-relevance) (1) in vitro dissolution tests show different (the so called “discriminatory”) results, but the in vivo results are similar (2) in vitro dissolution test show similar results, but the in vivo results are not similar i.e. bio-in-equivalent.

In the first scenario, the most likely cause is that the test may have been conducted using much softer conditions (in particular, related to stirring/mixing) under the “requirements” of obtaining “discriminatory” results. For example, if the formulations of the two products are such that one hides the drug (API) better than the other at the bottom of the vessel then one will observe different in vitro dissolution results, but most likely similar in vivo results. Drugs with low aqueous solubility and/or of low content would show such a problem. This is the most commonly observed issue with the use of paddle/basket apparatuses as these provide poor, and/or lack of, stirring and mixing required. Commonly such tests are referred to as “overly discriminatory”. However, in reality these tests are incorrect tests, mostly because of the incorrect choice of a dissolution apparatus.

In the second scenario, the most likely cause would be of chemical nature, such as an interaction between a drug and an excipient. It is possible that during dissolution testing, a complex has been formed or dissociated, with much higher solubility, which may not be the case in vivo. The likely suspect, in this case, maybe the pH of the medium. One should make sure that the pH of the medium has not been inadvertently increased as this will certainly cause this problem (use of larger amounts of SLS may be a prime suspect here). Some focus on the chemistry aspect of the product (drug excipient interaction) would be very helpful.

The next consideration should be given to the use of the paddle/basket apparatuses themselves. If possible, avoid using these apparatuses as these can be the main cause of the problem. Even if you are going to try the suggestions provided above, the use of a paddle/basket may hinder in establishing the cause of the problem. Consider using an apparatus that will provide efficient and reproducible mixing and stirring.

One of the requirements to conduct an appropriate drug dissolution test is to use a sufficient volume of dissolution medium, which should dissolve the expected amount of drug released from a product. This ability of the medium to dissolve the anticipated amount of drug is known as a “sink condition.” It is important to note that a dissolution test should not be conducted in a medium volume that would not dissolve the expected amount of the drug completely and freely. This is because of the obvious reasons that even if a product contains and releases 100% of the drug as expected, one cannot measure (quantify) it because for quantitation/sampling, the drug has to be in the solution. Therefore, it should be noted that this requirement of “freely soluble” or “sink condition” is the requirement for the quantitation (analytical chemistry) and has nothing to do with the physiological aspect. Considering that oftentimes limited volume is available for in vitro dissolution testing, such as with the vessel-based apparatuses, one is required to add some solubilizing agent (e.g., SLS) to create the sink condition for quantitation of the drug.

It is to be noted that a physiological environment deals with the availability of limited volume in a completely different manner. Here, the drug is continuously absorbed into the blood, metabolized, and eliminated, which provides a very efficient mechanism for providing a high solubility equivalent.

On the other hand, the limitation of having a smaller volume in vitro is compensated by the use of a solubilizer. It is very important to note, as has been highlighted in other situations, that to conduct a dissolution test, an analyst needs to simulate, not duplicate, the in vivo environment. This can be explained with an analogy of using a mercury thermometer to monitor body temperature. One does require duplicating the body’s mechanism to monitor the temperature. A human body does not have or require a mercury thermometer to monitor or maintain the body temperature. Furthermore, it also does not care what amount of mercury and what length of thermometer one uses. It is for our own convenience that we use mercury thermometers with the objective that we like to know the temperature of the body at a certain time point.

Similarly, for dissolution testing, we would like to see how a product will behave (release) in a physiological environment represented by an aqueous-based medium with a pH of 5 to 7. If the product is of a highly soluble drug, the analyst needs not do anything further except take the sample and measure the drug to finish the experiment/test. On the other hand, if it is required to test a product having the same formulation as in the previous case but with a low solubility drug, then the analyst may face a problem of quantitation. To address the problem of quantitation, the analyst is required to modify the medium so that it solubilises the drug but should remain physiologically relevant. Therefore, equivalents such as sodium lauryl sulphate are used as the solubiliser for bile salts, which are present in the GI tract.  Thus, an analyst must first establish if a solubilizer will be required or not to meet the requirement of dissolving the expected amount of drug in the desired volume of the medium, commonly 900 mL.

Another requirement for the sink condition, often described in the literature, is that of the multiples (2x, 3x, 5x or 10X, etc.) of volumes of medium over and above the volume needed to saturate the medium with the expected amount of drug. It is very important to note that the only requirement for a sink condition is that the volume of the medium should be such that it would provide complete dissolution of the expected amount of the drug. Generally, this condition is fulfilled if an analyst uses a little more (10 to 15%) volume than the volume of the medium (with or without solubilizer) required to dissolve the expected amount of the drug. The multiples as noted above and often described in the literature have no scientific basis and are not supported by any experimental evidence. Therefore, analysts can easily ignore such requirements, if they choose, without any deleterious impact on the dissolution testing or product evaluation.

In short, a sink condition is solely an in vitro requirement which is required to quantify the drug when it is released and dissolved in a dissolution medium. The sink condition may be defined as the volume of dissolution medium, with or without a solubilizer, needed to provide complete dissolution of the expected amount of drug present in the product. One may use any multiple of this volume if so desired. However, scientific and experiment studies do not provide any support to such a requirement or practice.