1. Content uniformity of drug: A known weight of ointment is taken and assayed for the amount of the drug.
2. Penetration: A weighed quantity of ointment is rubbed
over the skin for a given period and unabsorbed ointment is collected and
weighed. The differences in weights represent the amount absorbed.
3. Rate of release of medicament: To assess the rate of
release of medicament, a small amount of the ointment can be placed on the
surface of nutrient agar contained in a
Petri dish. If the medicament is bactericidal the agar plate is
previously seeded with a suitable organism like S. aureus. After a suitable
period of incubation, the zone of inhibition is measured and correlated with
the rate of release.
4. Absorption of medicament into the bloodstream: Ointment
should be evaluated for the rate of absorption of drug into the bloodstream.
This test can be run in vivo only. A definite amount of ointments should be
rubbed through the skin. Under standard conditions, medicaments are estimated
in the blood plasma or urine.
5. Irritant effect: In general no ointment should possess an
irritant effect on the skin or mucous membranes the tests for irritancy can be
carried out on the skin and eyes of rabbits or the skin of human beings. The
irritant effect can also be judged to a certain extent by injecting the
ointment into thigh muscles and under the abdominal skin of rats. Reactions are
noted at intervals of 24, 48, 72 and 96 hours. Lesions on the cornea, iris, and
conjunctiva are used for judging the irritancy to the eyes. The presence of
patches on the skin within 2 weeks indicates irritancy to pressing skin.
6. Consistency test: Using penetrometry.
Procedure: Preparation of test sample: Three methods (A, B, C).
A: Carefully fill three containers without forming
air bubbles. Level it if necessary to obtain a flat surface.
B: Apply a suitable shear to the samples for 5
minutes carefully and fill three containers without forming air bubbles. Level
it if necessary to obtain a flat surface.
C: Melt three samples carefully and fill three
containers without forming air bubbles. Level it if necessary to obtain a flat
surface.
Determination of Penetration
Place the test sample based on the penetrometer. Verify that
its surface is perpendicular to the vertical axis of the penetrating object.
Bring the temperature of the penetrating object to 25 ± 0.5°C and then adjust
its position such that its tip just touches the surface of the sample. Release
the penetrating object and hold it free for 5 sec. Clamp the penetrating object
and measure the depth of penetration. Repeat the test with the two remaining
containers.
1. Rheology: The rheology or viscosity should remain
constant. As creams are normally non-Newtonian, the viscosity can be measured
using viscometers used for such liquids. Rheologic measurements are utilized to
characterize the ease of pouring from a bottle, squeezing from a tube,
maintaining product shape in a jar, etc.
2. Sensitivity: As various types of ingredients are
used with the occasional use of antiseptics hormones etc. there is a
possibility of sensitization or photosensitization of the skin. This test is
normally done by a patch test. The test sample is applied along with a standard
market product at different places and the effect is compared after some time.