Section <795> of the USP 24/NF19 Supplement 1 requires that the capsule, "shall
not be less than 90% and not more than 110% of the theoretically calculated
weight of each unit." This "weight variation" requirement (discussed in Section
<905> of the USP 24/NF19) measures the variability in the amount of powder contained
in each capsule. This procedure can be carried out in all pharmacies.
The other Dosage Form Uniformity test of Section <905> is "content uniformity"
which measures the variability in the amount of active drug contained in each
capsule. Most pharmacies are not equipped to carry out content uniformity analyses
since special analytical equipment is required.
It is possible to have capsules that pass the weight variation requirement
but not have content uniformity. This can occur if the material put into the
capsules is not a homogenous mixture of all the ingredients. Some capsules would
then have more active drug than other capsules. Appropriate mixing (i.e., geometric
dilution) of all capsule ingredients into a homogenous mixture before filling
the capsules. In this manner, the weight variation data will be sufficient to
ensure the quality of the capsules.