Question and Answer Section — February 2014

William Brown and Margareth Marques
The following questions have been submitted by readers of Dissolution Technologies. Margareth Marques, Ph. D. and Will Brown, United States Phamacopeia, 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: web@usp.org

Q The dissolution test in a particular USP monograph uses pooled sampling. We would like to do a dissolution profile comparison using f2 for this product. Can we use the pooled sample results for the calculation of f2?
A Pooled sample results should only be used for routine quality control analysis and only if the USP monograph calls for it. For product development and for comparison of dissolution profiles using 2 or any other approach, you need to use individual results from each time point from each vessel. Information on the variability of the results is lost when using pooled samples.

Q When we do the acid stage in the dissolution test for pantoprazole sodium delayed-release tablets, we observe that pantoprazole degrades in the 0.1 N hydrochloric acid medium, and we can't quantify the amount released in the acid stage. What could be done to solve this issue?
A Pantoprazole, omeprazole, lansoprazole, and all the other members of this family of compounds are unstable in acid medium. This is the reason they are formulated as delayedrelease capsules or tablets. Instead of measuring the amount of drug substance released into the acid-stage medium of the dissolution test for a dosage form containing this type of compound, you can measure the amount of drug substance that still remains in the dosage form. You can do this determination using the assay method or the content uniformity procedure.

Q Can you explain the reasons for the Tier 1 and Tier 2 methods in the ziprasidone capsule dissolution test recommended in the FDA database for dissolution methods ( http://www.accessdata.fda.gov/scripts/cder/dissolution/index.cfm )?
A Gelatin in the presence of certain compounds and in high humidity and high temperature conditions can cross-link. See USP General Chapter <1094> Capsules-Dissolution Testing and Related Quality Attributes, published in Pharmacopeial Forum 39(3) (available free of charge at www.usppf.com) and scheduled to be official in the First Supplement of USP 37. Cross-linked gelatin is insoluble in aqueous solvents. When gelatin cross-linking occurs, the USP General Chapter <711> Dissolution recommends adding enzymes to the dissolution medium.

Enzyme activity may be compromised in the presence of surfactants. If there is any surfactant in the dissolution medium for the dissolution testing of gelatin capsules, there may be a need for a pretreatment where the capsules are exposed to the dissolution medium without the surfactant for not more than 15 min, after which the surfactant is added to the medium.

In the case of ziprasidone capsules, the dissolution test is run using the medium specified in the FDA database for Tier 1. Only if the product has cross-linked gelatin will you run the test with the conditions stated for Tier 2.

Q Three-stage dissolution acceptance criteria for delayed-release products allow one unit out of 24 units tested to release NMT 25%. Considering that the drug product is subjected to acid-stage dissolution to test the integrity of the enteric coat by allowing negligible drug release (typically 10%), what is the rationale for adopting a three-stage specification for the acid stage of delayed-release drug products?
A The delayed-release acceptance criteria and procedure in the USP General Chapter <711> Dissolution reflect the entire test, acid and buffer stages. The requirement that no result is greater than 25% is a zero-tolerance criterion that guards against complete failure of the delayed-release mechanism, while the requirement that the average is not more than 10% forces most results to considerably lower values. The acid-stage criteria are the same at A2 and A3 levels. The A3 level of test is required because the buffer-stage testing does have three distinct criteria. If testing proceeds to B3, the acid-stage testing precedes that testing, and for whatever reason, no difference from the previous acid stage is expected.

Q The acceptance table for immediate-release dosage forms in the USP General Chapter <711> Dissolution has three stages. Is this wide allowance of variability in dissolution testing motivated by expected variability in the results or is it statistically motivated?
A Q is based on observed performance of therapeutically satisfactory product. The dissolution test criteria apply to any marketed product conforming to the monograph and must allow for product differences. The product must conform with the dissolution test from manufacture to expiry. One can argue that the test needs to balance control of performance variability against the risk of unnecessary removal of therapeutically acceptable product from the marketplace. The approach taken in <711> for immediate-release products reflects three decreasingly strict sets of criteria, S1, S2, and S3. However, studies have shown that if S3 testing is needed, the probability of passing is not greater than what is given at S2. Products that must proceed to S3 are not likely to pass the test at that stage.

Q In the USP General Chapter <711> Dissolution under Procedure Apparatus 1 and Apparatus 2 Delayed-release Dosage Forms Method A is a note in the Buffer Stage that states "NOTE- Complete the operations of adding the buffer and adjusting the pH within 5 minutes," which gives a time limit between the Acid Stage and the Buffer Stage. However, Method B only specifies to "proceed immediately as directed under Buffer Stage." Does "immediately" give an actual specified time limit that the dosage form must be transferred from Acid Stage to Buffer Stage for Method B, such as within 5 min like Method A?
A The rationale for putting a limit on the time taken to convert from acid-stage conditions to buffer stage for delayed-release products is two-fold. First, the assault on the acid-resistant mechanism is one stage of the test. Continuing this condition for longer than the time indicated in the dissolution procedure could possibly result in additional degradation of the acid resistance and subsequent release of the drug substance. Any drug substance released after the acid-stage sampling will not be accounted for by the test. Secondly, the start of the buffer stage should allow for little variability in the time of buffer exposure for the individuals units under test. Even without stirring, product exposed to the bufferstage medium will likely begin to react. In their wisdom, the USP experts found that a 5-min interval was acceptable for Method A. As Method B has no such well-defined limitation, a fair starting point might be to adopt the same limit as in Method A. Obviously, a shorter interval represents better control of the experimental sources of variation.

Q A product that shows dissolution of more than 85% of the label claim in 15 min is considered a product with "very rapid" dissolution. When both the test and reference products meet this criterion, they are considered to have similar dissolution behavior even without dissolution profile comparisons such as by f2 calculations. Can intrinsic dissolution rate be treated similarly? Specifically, is there a definition for "rapid" or "very rapid" intrinsic dissolution rate?
A We are not aware of a classification of compounds based on rapid dissolution rate observed for intrinsic dissolution testing. Results from intrinsic dissolution testing are very much subject to experimental conditions and are not very reproducible. Therefore, it is not clear what value a criterion based on the observed intrinsic dissolution rate might offer.

Q I saw a scientific paper on dissolution testing where the dissolution test was performed at 25 °C and at 47 °C. What could be the rationale for using these temperatures instead of 37 °C?
A The temperature used in the dissolution test should be the temperature of the site of application of the product. For products with internal application, including vaginal and urethral routes of administration, the temperature of the test should be 37 ± 0.5 °C. For products applied to the skin, the temperature of the test should be 32.0 ± 0.5 °C.

It was observed that when an oral solid dosage form is taken with a liquid, the temperature of the fluids in the stomach is going to be momentarily at about 20-25 °C, and with time, it will return to around 37 °C. This may be a reason for starting the dissolution test with a temperature of 20-25 °C.

There are some papers in the literature saying that in the case of certain extended-release dosage forms where the product is going to remain in the site of application for long periods of time, in general several months, it may be possible to reduce the duration of the dissolution test if the temperature of the test is higher than 37 °C. One example of such a product is a colloidal system (liposomes, nanospheres, microspheres, etc.) applied as a subcutaneous depot. In this case, the drug substance will be released at the site of administration over several months. To avoid running the dissolution test for the release time in vivo, the release of the drug substance can be accelerated by increasing the temperature of the test. In cases like this, a correlation between the dissolution test in real time and under accelerated conditions must be demonstrated. One of the possible problems that may make this correlation invalid is that the release mechanism of the dosage form may be altered at temperatures higher than 37 °C. FDA has already approved a product with a dissolution test that is carried out at 45 ± 0.5 °C. See the entry for dexamethasone intravitreal implant at http://www.accessdata.fda.gov/scripts/cder/dissolution/index.cfm

Q Our active ingredient is semisolid and has low solubility in aqueous solvents. We are preparing the standard stock solutions using 20% acetonitrile, and the further dilutions are done with dissolution medium. We found high variability in the recovery study. Is it acceptable to use other diluents other than the dissolution medium?
A The procedure for the dilution of the standard and sample solutions will depend on your quantitative procedure. Ideally, the sample and standard solutions will have the same solvent composition to give the appropriate accuracy and precision. After you filter the sample solution, provided the filter system was properly validated, you can manipulate the sample solution as necessary. Instead of matching the composition of the standard solution to the sample solution, you may arrange the diluents to match the final composition of the sample solution to the standard solution. In any case, the entire procedure must be validated.

Q What is the acceptance criterion for accuracy when validating a dissolution method for a modified- release dosage form? What is the limit of drug recovery after the first sampling?
A There are no defined acceptance criteria for accuracy. Allowable accuracy of a method should be viewed in the context of the effect that bias may have on the results of the test that will also depend on the formulation and manufacturing process. The acceptance criteria for accuracy are defined in a case-by-case approach.

Q The USP general chapter gives instructions to withdraw the dissolution samples within 2% of the specified time points. How can this be done if we are running a dissolution profile? Is the use of autosamplers allowed?
A It is up to the lab to decide what is the most appropriate sampling procedure. The General Chapter <711> Dissolution allows the use of manual, semiautomatic, or automatic sampling. You need to verify that the chosen procedure gives results similar to those obtained with the standard apparatus described in <711>. The General Chapter <711> specifies that the sampling should be done at the stated times within a tolerance of ±2%. If you have a sampling time of 5 min, the sampling can be done within the interval of 5 min ± 6 sec. If manual sampling will be used, it may be necessary to stagger the introduction of the samples to keep within this required tolerance. You are going to introduce a delay after each sample is introduced into its vessel before placing a sample in the next vessel. The time you wait should accommodate the sampling time and any treatment that the analyst will need to perform so that the analyst will be free to promptly withdraw the next sample.

Q Is it mandatory to check the disintegration time of all individual tablets during the disintegration test or can we record only the time for the last tablet disintegrated?
A Although the USP disintegration test only puts a time limit on the disintegration of all units tested, you will want to check the individual times. A good disintegration test is discriminative for the critical quality attributes of your product. The behavior of your product during the test can give you indications of possible deviations in product performance that can signal other manufacturing problems.

Q What should be the action if a product is passing the dissolution test with very good results but fails disintegration?
A Orally disintegrating tablets are the only dosage form that requires both disintegration and dissolution tests. All other solid oral dosage forms require either a dissolution or a disintegration test. Not all solid oral dosage forms disintegrate. Some tablets, such as those with a release mechanism by erosion, will disintegrate partially, and others, such as osmotic-pump tablets, will not disintegrate at all during the dissolution test.

Q How is the disintegration test performed if the length of the tablet is too long?
A The disintegration test is not required for all products. The dissolution test is seen as a more comprehensive test and needs to be developed first. Then, depending on the characteristics of your product (release mechanism and BCS classification of the active ingredient) and how it behaves during the dissolution test, it may be possible to replace the dissolution test with a disintegration test, but the decision needs to be supported by data. In the USP General Chapter <2040> Disintegration and Dissolution of Dietary Supplements there is a description of a disintegration apparatus that may be used for larger tablets or capsules.

Q In the USP General Chapter <711> Dissolution it says that the sinker can be a few turns of wire helix or the basket described in Figure 2a. Can other types of sinker be used? Is the size of the sinker universal for all capsule sizes?
A Sinker size and design can have a very big impact on the dissolution profile, and they need to be selected in a caseby- case approach. There are several different types and sizes of sinkers available on the market in addition to the wire helix that can be made in the lab. You need to select the one that is the most appropriate for your product. Capsules are going to swell when they are hydrated, and the size and shape should take this into consideration.

Q Can we use plastic pipettes to withdraw the samples from the dissolution vessel?
A The withdrawal and filtration of dissolution samples should be done as fast as possible to interrupt the dissolution process. Pipettes will complicate sample handling including the effect of the transfers that will be necessary in filtration. Use of a stainless steel cannula bent in an L shape and a large volume plastic or glass syringe is recommended. An additional concern is that some compounds adsorb to plastic and others to glass. Therefore, you need to select the type of syringe in a case-by-case approach.

Q What should be the limit for extraneous and unknown peaks in the chromatographic quantitative procedure used in the dissolution test?
A There are no official guidances regarding this issue. Unexplained peaks should be investigated for possible causes and ways to eliminate or minimize them. Some of the sources of these peaks could be the quality of reagents including any surfactants used to prepare the dissolution medium, filters and the filtration step, and chromatographic columns.

Q Can sink condition be defined as the relationship of the concentration of the drug substance in a saturated solution and the concentration of the drug substance in 900 mL of medium?
A To determine the sink condition you need to know the solubility of the drug substance in various dissolution media within the physiological pH range at 37 °C. From this information, the volume of dissolution medium needed to obtain a saturated solution is calculated considering the highest dose of the product that will be marketed. To meet sink condition, you need to use a volume of medium at least three times this value.

Q What is the performance verification procedure for USP Apparatus 6 (rotating cylinder)?
A There is no specific performance verification procedure for USP Apparatus 6. The best approach would be to do the mechanical verification and Performance Verification Test (PVT) as for USP Apparatus 1.

Q If a gelatin capsule fails the dissolution test and enzyme is going to be added to the dissolution medium, should we repeat the test at S1 or S2 level?
A We are aware that the text in USP regarding the failure of dissolution testing of capsules is not very clear, and we are working on its revision. If the capsule fails the dissolution test because of cross-linking in the gelatin shell, the test can be repeated at S1 level using enzymes. You do not need to complete the test in the medium without enzymes if cross-linking has been proved. If the capsule is failing the test for reasons other than cross-linking, adding the enzyme to the dissolution medium is not going to solve the problem, and in this case, the test is continued at the S2 and S3 levels as appropriate.

Q What are the concentration and brand name of the pepsin to be used in the dissolution test of capsules?
A You can use any pepsin with high activity. The higher the activity the better; in this case, a smaller amount of enzyme is used and will facilitate the handling of the samples. You need to determine the activity of the enzyme before use employing the procedure described under Pepsin, purified in the Reagents Specification section of USP. This procedure is under revision, and its last version was published in Pharmacopeial Forum 39(6) (available free of charge at www.usppf.com). We received several comments regarding this procedure, and a revision will be published in a future issue of Pharmacopeial Forum. Using the experimentally determined activity, you are going to calculate the amount of enzyme to be added to the medium according the instructions in the USP General Chapter <711> Dissolution.

Q Is there any guidance or precedent for using product dissolution stability data to establish product shelf life? ICH and FDA guidances are focused on assay or degradation product stability data to calculate the trend. If we need to perform trend analysis of dissolution data, we are in a dilemma as to whether to use individual data or the mean value at each time point.
A The answer to this question was provided by Kim Huynh-Ba (kim.huynhba@pharmalytik.com).

Shelf life should be calculated based on all data, not just assay, degradation products, pH, moisture, or dissolution. Similarly, trend analysis should be done with data of all tests listed on the product's specification. Any undesired trend could affect the shelf life. However, there are no regulations on how trend analysis is to be done for any test. Justification is needed if trend analysis is done on data collected differently than what the product specification states.

Q In the dissolution or drug release testing of capsules, if the capsule shell interferes in the quantitative procedure, can we remove the contents from the capsule for the test?
A The test should be run with the dosage form that the patient is going to use. If the patient is going to swallow the entire capsule, the dissolution or drug release test should be done with the entire capsule. If the patient is going to open the capsule and disperse the capsule contents in a liquid or in some kind of food, the dissolution test should be done with the capsule contents.

Several alternatives can be evaluated if the capsule shell interferes with the quantitative procedure: (1) Use another analytical technique; if the current procedure is by spectrophotometry, it can be replaced by a chromatographic procedure. (2) Prepare a solution with only the capsule shell dissolved in dissolution medium and make any corrections based on its response in the analytical procedure. (3) Use the second derivative if the quantitative procedure is by spectrophotometry. (4) Use an alternative wavelength if the quantitative procedure is by spectrophotometry. (5) React the interfering compound with a reagent to create a product that does not absorb at the analytical wavelength.