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
We hired a vendor to do the mechanical
verification of our dissolution equipment. After its
completion, we started doing the performance
verification, and one of the vessels broke during
this evaluation. Should we start the performance
verification all over again? Should we call the
vendor back to do another mechanical verification
of the equipment after replacing the broken vessel?
A
The influence of the vessel on the dissolution
results has been the subject of a number of papers in
the literature. Therefore, we should assume that a
new vessel will influence the performance of the test
platform. Mechanical verification by the vendor other
than evaluation of the conformance of the new
vessel to USP is not essential. Please review the
Dissolution Toolkit available on the USP website for
advice on the mechanical calibration variables
associated with the vessel. An additional PVT will be
necessary in this case. The PVT now evaluates the
performance of the integrated test platform, and
evaluation of just one element is not possible. You
can see that the criteria are applied to the summary
statistics (geometric mean and %CV) of the 6, 7, 8, or
12 positions and not to only one position. We have
cause to assert that the evaluation of the system
as a whole provides better understanding and
control of its performance in the dissolution test.
You can see the list of references in the Dissolution
Toolkit,
http://www.usp.org/pdf/EN/dissolutionProcedureToolkit2010-03.pdf
Q
Based on USP Genera l Chapter <711>
Dissolution for immediate-release dosage forms
(Apparatus 1 and 2), unless otherwise specified,
each unit dose is tested individually. The Procedure
for a Pooled Sample for Immediate-Release
Dosage Forms states to "use this procedure where
Procedure for a Pooled Sample is specified in the
individual monograph." Since the pooled sample
approach does not allow for the verification of
tablet variability, is it acceptable to test each unit
dose individually in lieu of the pooled-sample
approach, even if the Procedure for a Pooled
Sample is specified in the individual monograph? If
this approach is acceptable, which acceptance
criteria would apply in this situation, Acceptance
Table 1 (for the individual unit dose results) or
Acceptance Table for a Pooled Sample (using the
average of the individual results instead of the
pooled-sample result)?
A
The use of pooled samples was introduced in USP
several years ago to try to reduce the number of chemical
analysis carried out. The use of this procedure was allowed
only for immediate-release dosage forms with active
ingredients that have neither bioavailability problems nor
narrow therapeutic ranges and a long history of dissolution
results. There are only 79 USP monographs that allow the
use of pooled sampling. The drawback of this procedure is
that it does not allow monitoring the inter-unit variability
in the dissolution results. If the monograph calls for the
pooled-sample procedure, the dissolution test can be
carried out by collecting individual unit values for quality
control purposes, but the average value would still have to
be subjected to evaluation using the pooled-sampling
criteria.
Q
In the USP procedure for the performance
verification of USP Apparatus 1 and 2 using the USP
Prednisone Tablets RS, the acceptance criteria are
27-38% GM for Apparatus 2 and 60-71% GM for
Apparatus 1. Why are acceptance criteria different
for both Apparatus using the same reference
standard?
A
USP Prednisone Tablets RS are a disintegrating dosage
form. Differences between the paddle and basket include
the formation and maintenance of a cone under the
disintegrating tablets (paddles) and the ability of the
disintegrated material to exit the basket upon reaching a
40-mesh size. We can speculate that during paddle testing,
cone formation may reduce the prednisone dissolution
rate relative to that during basket testing. Additionally,
both the better agitation of the medium for the tablet
residue remaining within the basket as well as the size
reduction and deaggregation promoted by the sieving
action of the basket mesh increase the dissolution rate
relative to the paddle. However, the underlying issue in
your question can be answered simply by noting that the
dissolution rates are what they are. The ranges reflect
observed results from a multiple center, collaborative
study that includes laboratories in North and South
Americas, Europe, and South Asia.
Q
What is the right procedure for using a cannula for withdrawing
dissolution samples? Should the cannula be kept inside the medium from the
moment we start the dissolution testing, or should it be kept out except while
withdrawing the sample? If doing a dissolution profile with the cannula removed
except for sampling, it will be repeatedly inserted and removed.
A
The presence of any device inside the dissolution vessel
is going to affect the hydrodynamics of the dissolution
medium. The extent of this perturbation needs to be
investigated for each product analyzed through the
evaluation of the impact on the dissolution profile. The
most appropriate sampling procedure needs to be
evaluated in a case-by-case approach. Once the best
condition has been identified, it needs to be carefully
described in the final documentation for the dissolution
procedure.
Q
What should be the maximum volume that can
be sampled during dissolution? Could it be 10% or
more of the total volume?
A
There are no limits for the amount of solution with-
drawn during the dissolution test. It should be the smallest
amount possible to minimize the interference in the
results, and it depends on the quantitative procedure used
to quantify the amount of drug substance released. In the
case of dissolution profiles, it is recommended to replace
the amount of medium withdrawn with the same amount
of previously warmed dissolution medium, and appropriate
corrections in the calculations are necessary to account for
the removal of drug substance from the vessel and the
dilution of the remaining solution in the vessel.
Q
During dissolution testing of a particular tablet
product, bubbles form and stick to the tablet,
decreasing the final dissolution results. Sometimes
the bubbles form in the basket even without a
tablet. We tried to use the USP degassing procedure
(heating up to 41 °C and filtering under vacuum)
and helium sparging. In both situations, bubble
formation was observed. Could you please
recommend the best practices to avoid bubble
formation?
A
Bubble formation is evidence of supersaturation of
gaseous material. The bubbles will form on heterogeneous
surfaces such as the basket and the sample tablets. The
observation of lower dissolution results when bubbles
form on the tablets or baskets is not unexpected because
the bubbles will retard the transfer of dissolved drug from
the solution inside the basket to the bulk medium and
could also occlude the dissolving tablet surface reducing
mass transfer there. That being said, the reduction of
dissolved gas content should be accomplished to a level
where bubble formation does not interfere with the
dissolution test. The deaeration procedure described in
USP General Chapter <711> Dissolution has been shown
to reduce the dissolved gas level of water to the point
where it does not interfere with the dissolution of USP
Prednisone Tablets RS. Please note that the degassed
medium state is unstable and quickly re-equilibrates to a
saturated state. Therefore, the careful handling and
transfer of the medium is called for, as is its prompt use.
Allowing the medium temperature to drop below 37 °C,
incautious pouring resulting in turbulent mixing with air,
and stirring to accelerate temperature equilibration will
adversely affect the quality of the medium. Helium has a
low solubility in water that can lead to saturation if the
medium is treated with helium at room temperature. In
that case, the bubbles could be composed of helium. A
revision paper comparing the effectiveness of the various
deaeration procedures was published in Dissolution
Technol. 2004, 11 (1), 6-11.
Q
The following text is in the ICH Guidance Q1E
(Evaluation of Stability Data):
"2.4.2 Significant change at accelerated condition
Where significant change* occurs at the
accelerated condition, the retest period or shelf life
would depend on the outcome of stability testing at
the intermediate condition, as well as at the long-
term condition.
*Note: The following physical changes can be
expected to occur at the accelerated condition and
would not be considered significant change that
calls for intermediate testing if there is no other
significant change:
From a regulatory point of view, this means that
during stability (accelerated or long term), the
dissolution test can fail because of cross-linking
(even using the highest concentration of enzymes
allowed by USP or other pharmacopeias) and not
be considered a significant change. Can you
comment?
A
Cross-linking in gelatin capsules is going to happen
eventually. When it is unequivocally observed as a part of
the accelerated conditions, it will not be a cause of further
testing by the intermediate conditions. It can be mini-
mized or avoided depending on how the product is
formulated, how the packaging material and storage
conditions are selected, and by some type of pretreatment
of the gelatin capsules. The information available in the
literature regarding all aspects of cross-linking in gelatin
capsules is very extensive. In most cases, the presence of
cross-linking does not affect in vivo behavior because in
vivo there are enzymes, bile salts, and so forth, that will
promote the opening of the capsules. This is the reason for
not considering the presence of cross-linking as a signifi-
cant change. Caution is necessary to determine if the
degree of cross-linking affects in vivo performance and if
the capsules are really failing dissolution because of the
presence of cross-linking. If the capsules are opening and
releasing their contents to the medium, even though they
are failing the dissolution test, the failure is not caused by
cross-linking. It is necessary to verify visually if the dissolu-
tion failure is really due to cross-linking and not because
of problems with the capsule content or because the
dissolution conditions are not appropriate. If the capsules
are not opening even with the addition of enzymes to the
medium, it is necessary to investigate the possible reasons:
if the right quality of enzyme was used, if the activity was
determined using the appropriate procedure just before
use, if there are any compounds in the formulation or in
the dissolution medium that could inactivate the enzyme,
and so forth. There are some reports stating that the
enzymes and the conditions in the USP General Chapter
<711> Dissolution are not always appropriate for all
products. Depending on the formulation and the compo-
sition of the dissolution medium, it may be necessary to
use higher concentrations of pepsin or pancreatin or other
types of enzymes. If this is the case, the alternative
conditions for the test should be investigated and
properly justified.
Q
One of our products shows erratic dissolution
results using the 40-mesh basket, even though it
gives otherwise acceptable performance. We would
like to know if we could use other types of baskets
such as the 20-mesh basket in the dissolution
testing?
A
There are baskets with other opening sizes that can be
used in cases such as the one described. There are 20- and
10-mesh baskets available that can be evaluated. It may
even be the case where paddles and sinkers may be useful
because the formulation can clog the other mesh size
baskets.
Q
During a dissolution test, we find that if we
centrifuge the sample, any undissolved particles
will be dissolved giving a high bias. Hence,
centrifugation is not advisable for dissolution
testing. Please, comment.
A
When developing a dissolution test or when evaluating
the suitability of a dissolution test from the literature (from
a paper or pharmacopeial monograph), the dissolution
procedure must be evaluated for the appropriateness to
the formulation under study. This evaluation should be
done in a case-by-case approach. If the decision is made to
filter the sample, the appropriate pore size and type of
membrane should investigated for the product under
evaluation. If centrifugation is going to be used, it is
necessary to define appropriate time and speed. There are
some situations where centrifugation is the choice even if
it is not the best method. One example is if components of
the filtering system interfere with the quantitative
procedure, as in the case of quantitation of the amount of
estrogens dissolved using fluorescence.
Q
What is the appropriate method to determine
sink condition? I am developing a dissolution test
with the quantitative step by HPLC, and the ideal
working concentration for this HPLC method is
1 mg/mL. My tablet has a 500-mg label claim, there-
fore I would like to work with 500 mL of dissolution
medium to have a final concentration of 1 mg/mL,
but the dissolution results I am obtaining are not
good. What could I do to improve the method?
A
Sink condition is determined relative to the highest
product dose that will be marketed. The solubility, in units
of mass/volume, of the active pharmaceutical ingredient
should be determined at 37 °C using dissolution medium
in the physiological pH range. The most used solubility
method is the one that determines the equilibrium
solubility, but other techniques can be used. Details of
these procedures can be found in the literature. A com-
monly used definition is that the volume of dissolution
medium is at least three times the volume necessary to
obtain a saturated solution. Alternative definitions give
five times or even ten times this volume. In some cases
more discriminative dissolution methods are developed
when sink conditions are not met. The quantitative
procedure to determine the amount of drug substance
released in the medium should be linear considering all
points in the dissolution profile. This means that in some
situations, the analytical procedure used in the assay of
the active ingredient in the dosage form may not be
suitable to be used in the dissolution test. The quantitative
procedure used in the dissolution test must have the
appropriate linearity, accuracy, and precision for all points
in the dissolution profile.
Q
We purchased 2-L dissolution vessels for the
dissolution evaluation of 400-mg carbamazepine
extended-release tablets. Must the Performance
Verification Test using USP Prednisone Tablets RS
be performed with this 2-L vessel?
A
The inner diameters of the 2-L and 1-L vessels used in
USP Apparatus 1 and 2 are similar. The use of USP
Prednisone Tablets RS should be a valid performance
verification probe for the 2-L vessels. Sampling the
dissolution medium in the taller 2-L vessels may present
additional difficulty, but with that overcome, the
procedure could be followed.