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.