Questions and Answers August 2023

Margareth R. Marques, Ph.D. and Mark Liddell, Ph.D.
The following questions have been submitted by readers of Dissolution Technologies. Margareth R. Marques, Ph.D., and Mark Liddell, Ph.D., United States Pharmacopeia (USP), authored responses to each of the questions. *Note: These are opinions and interpretations of the authors and are not necessarily the official viewpoints of the USP.
Email for correspondence: mrm@usp.org

Q In USP general chapter <711> Dissolution it is stated to add enzymes like pepsin and others to prevent cross linking of capsules shell, but when some capsules were analyzed with and without enzyme, no differences between with or without enzyme were found, and no cross-linking happened in medium without enzyme addition. Do you have any comments?
A As stated in the USP general chapter <711> Dissolution, enzymes can be added to the dissolution medium when there is evidence of the presence of cross-linking in gelatin capsules. The strongest evidence of cross-linking is observed when capsules do not open. The capsules may lose their shape, appear to be hydrated, but simply do not open and release the contents of the capsule. The presence of cross-linking in gelatin renders the capsule insoluble in aqueous solvents. When this occurs, enzymes are added to digest the cross-linked gelatin, not to prevent the cross-linking. See more information in the USP general chapter <1094> Capsules - Dissolution Testing and Related Quality Attributes and the following article: Marques MRC. Enzymes in the dissolution testing of gelatin capsules. AAPS PharmSciTech. 2014. doi: 10.1208/s12249-014-0162-3.

Q Can the use of traditional sinkers be completely replaced with the use of the stationary basket as described in the USP general chapter <711> Dissolution?
A No, while the stationary basket is a possible option when traditional sinkers are not suitable for a particular formulation, its use must be justified with experimental data obtained with the samples under evaluation.

Q If 0.1 N hydrochloric acid solution is used as dissolution medium, does it need to be standardized?
A No. There is a note at the end of each volumetric solution entry in USP - NF stating that if the volumetric solution is used for qualitative purposes such as dissolution medium, the solution does not need to be standardized.

Q Regarding the USP general chapter <701> Disintegration, could you provide a definition of what “softening” means?
A During the disintegration test the capsule is going to hydrate upon exposure to the disintegration media. The capsule will lose its shape and may have the appearance/ consistency of a gel or soft (malleable) material.

Q The USP general chapter <711> Dissolution states “Specimens are to be withdrawn only at the stated times, within a tolerance of ± 2%.” Does it mean that the sampling must be finalized by this time?
A For shorter sampling times, say around 5 min (time tolerance is only ± 6 sec), it may not be possible to complete the entire process of pulling the sample and filtering within the sampling time tolerance of ± 2%; however, the sampling and filtering need to be done as fast as practically possible to stop the dissolution process. This may be a particular challenge when using an autosampler with a fixed draw rate. The error in the sampling time will be dependent on both the rate of sample withdrawal and the volume of the sample at a given time point. The dissolution scientist should be aware of the uncertainty that this error may cause in the final dissolution profile.

Q If the acid stage criteria for a particular delayed-release product was met for the A1 level (no individual value exceeds 10% dissolved) but does not meet the buffer stage criteria for B1 level (each unit is NLT Q + 5%), does the acid stage need to be repeated along with the buffer stage? The statement “Continue testing through all levels unless the results of both the Acid Stage and Buffer Stage conform at an earlier level” is unclear and could be interpreted both ways in which both acid and buffer stages are repeated, or only the buffer stage is repeated because the acid stage met acceptance criteria at an earlier level.
A In the case of a delayed-release product, a single dissolution test consists of two phases, the acid stage and the buffer stage. As pointed out the acceptance criteria requires that “the results of both the Acid Stage and Buffer Stage conform.” Thus, you are going to use new samples and submit them to the acid stage, but you may not need to collect any samples at this stage because you have already verified the lack of release during the acid stage. After the appropriate time in the acid stage, proceed to the buffer stage where you will collect dissolution samples for quantitation.

Q While USP general chapter <711> states that the temperature inside the vessel should be 37.0 ± 0.5 °C, the USP general chapter <1092> The Dissolution Procedure - Development and Validation states that variations in temperature should be evaluated during the evaluation of robustness. Would successful robustness testing from 36-38 °C allow you to extend the range of the vessel temperatures?
A While it may be the case that the robustness of the temperature range for an individual dosage form may be wider than that of the compendial test requirements, the temperature of dissolution medium and all the other dissolution apparatus parameters must be kept within the compendial ranges when evaluating the robustness of a dissolution method.

Q Is there an optimal way of generating cross-linked capsules to produce consistent results to show the effectiveness and stability of the pepsin in the dissolution media? I found an article where capsule shells were exposed to 37% formaldehyde solution vapors for ~30 minutes in a desiccator, the capsules were filled with the capsule material, and the dissolution was performed. Is this the most efficient way or are there other means of evaluating this?
A Cross-linking is a kinetic process, so time plays a significant role in cross-linking, which may be observed in gelatin capsules. Capsules may need to stay several days under high temperature and high humidity to show cross-linking. Thirty minutes in a formaldehyde environment may not be enough to successfully generate cross-linking in gelatin capsules. The presence and extent of cross-linking may depend on not only the composition of the gelatin capsule but also the components contained within the capsule. As a result, determining ideal conditions to promote cross-linking may vary. See the following papers for additional information on forced cross-linking.
Gold TB, Buice RG Jr, Lodder RA, Digenis GA. Determination of extent of formaldehyde-induced crosslinking in hard gelatin capsules by near-infrared spectrophotometry. Pharm Res. 1997;14(8):1046-1050. DOI: 10.1023/a:1012105412735.
Digenis GA, Gold TB, Shah VP. Cross-linking of gelatin capsules and its relevance to their in vitro-in vivo performance. J Pharm Sci. 1994; 83:915-921. DOI: 10.1002/jps.2600830702.

Q We sometimes must review the validation of dissolution procedures, and quite often we cannot find the results from filter studies (do the filters release interfering compounds, adequate recovery with standard/sample at different levels, adequate filtration of undissolved particles, etc.) Is this information normally supposed to be documented in the validation, or is this kind of test more adequately documented during development stages?
A Filter evaluation should be done as early as possible in the development process and dissolution method validation project. In many cases, it is needed early on for the solubility assessment of the drug substance and for successive dissolution studies. The filter process may be re-evaluated later depending on the changes made in the formulation/manufacturing process. The filter should be evaluated regarding pore size to ensure that all solids in suspension will be retained. The filter materials should also be evaluated to ensure that there is no drug adsorption and no interference from possible leachables and extractables that may be part of the filter material or housing.