EVALUATION OF OINTMENTS

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The different methods of evaluation of ointments are
(1) Physical methods
  • Test of rate of absorption
  • Test of non-irritancy
  • Test of rate of penetration
  • Test of rate of drug release
  • Test of rheological properties
  • Test of content uniformity
(2) Microbiological methods
  • Test of microbial content
  • Test of preservative efficacy
PHYSICAL METHODS
TEST OF RATE OF ABSORPTION
Diadermic ointments are those from which the drug
moves into deeper skin tissues and finally into the systemic
circulation. Such ointments should be evaluated for the rate of
absorption of drugs. The ointment should be applied over a definite
area of the skin by rubbing. At regular intervals of time, serum and
urine samples should be analysed for the quantity of drug absorbed. The
rate of absorption i.e., the amount of drug absorbed per unit time
should be more.
TEST OF NON-IRRITANCY
The bases used in the formulation of ointments may
cause irritation or allergic reactions. Non-irritancy of the
preparation is evaluated by patch test. In this test 24 human
volunteers are selected. Definite quantity of ointment is applied under
occlusion daily on the back or volar forearm for 21 days. Daily the
type of pharmacological action observed is noted. No visible reaction
or erythema or intense erythema with edema and vesicular erosion should
occur. A good ointment base shows no visible reaction.
TEST OF RATE OF PENETRATION
The rate of penetration of a semisolid dosage form
is crucial in the onset and duration of action of the drug. Weighed
quantity of the preparation should be applied over selected area of the
skin for a definite period of time. Then the preparation left over is
collected and weighed. The difference between the initial and the final
weights of the preparation gives the amount of preparation penetrated
through the skin and this when divided by the area and time period of
application gives the rate of penetration of the preparation. The test
should be repeated twice or thrice. This procedure is tedious and not
followed anymore.
Using flow-through diffusion cell or microdialysis
method, the rate of penetration of the preparation can be estimated.
Animal or human skin of definite area should be collected and tied to
the holder present in a diffusion cell. The diffusion cell is placed in
a fluid bath. Measured quantity of the preparation is applied over the
skin and the amount of drug passed into the fluid is measured at
regular intervals by analyzing the aliquots of fluid using a
spectrophotometer.
TEST OF RATE OF DRUG RELEASE
A clean test tube is taken and the internal surface
is coated with the preparation as a thin layer. Saline or serum is
poured into the test tube. After a certain period of time, the saline
is analyzed for the quantity of the drug. The amount of drug when
divided by the time period gives the rate of drug release.
TEST OF RHEOLOGICAL PROPERTIES
The viscosity of the preparation should be such
that the product can be easily removed from the container and easily
applied to the skin. Using cone and plate viscometer the viscosity of
the preparation is determined.
TEST OF CONTENT UNIFORMITY
The net weight of contents of ten filled ointment
containers is determined. The results should match each other and with
the labelled quantity. This test is also called minimum fill test.
MICROBIOLOGICAL METHODS
TEST OF MICROBIAL CONTENT
Micro-organisms like pseudomonas aeruginosa and
staphylococcus aureus may contaminate the preparation and finally
infect the skin. So ointments should be tested for the absence of such
micro-organisms.
Solutions of different samples of the preparation
are made. Each sample is inoculated into separate volumes of 0.5 ml of
rabbit's plasma under aseptic conditions and incubated at 37 degrees C
for 1-4 hours. No formation of the clot in the incubated mass indicates
the absence of the micro-organisms.
TEST OF PRESERVATIVE EFFICACY
Using pour plate technique the number of
micro-organisms initially present in the preparation are determined.
Solutions of different samples of the preparation are made and mixed
with Tryptone Azolectin (TAT) broth separately. All cultures of the
micro-organisms are added into each mixture, under aseptic conditions.
All mixtures are incubated. The number of micro-organisms in each
sample are counted on 7th, 14th, 21st and 28th days of inoculation.
MICROBIAL LIMITS
On 14th day, the number of vegetative cells should not be more than 0.1% of initial concentration.
On 28th day, the number of organisms should be below or equal to initial concentration.
REFERENCES
  1. http://dictionary.sensagent.com/ointments/en-en/
  2. http://pharmtech.findpharma.com/pharmtech/data/articlestandard//pharmtech/112002/12404/article.pdf
  3. L. Lachman, H.A, Lieberman and J.L. Kanig, Theory & Practice
    of industrial pharmacy, Lea & Febieger, Philadelphia Latest Edn
  4. http://dictionary.sensagent.com/ointments/en-en/
  5. http://pharmtech.findpharma.com/pharmtech/data/articlestandard//pharmtech/112002/12404/article.pdf

About the Author

M Leela Keerthi's picture
Author: M Leela Keerthi

Comments

V.B.S.Aishwarya's picture

Nicely explained leela keerthi. Can you tell me some examples for ointment bases which may be irritant to skin?

Regards

V.B.S.Aishwarya

 

 

 

TK Indira's picture

well explained. Can you tell me the range of optimum viscosity to be employed while formulating ointments?

T.K. Indira. http://www.pharmainfo.net/tkindira

-- "Our greatest glory is not in never falling, but in rising every time we fall..." Team 'Char'minar.

Uma Pratyusha's picture

Hi Keerthi, Please tell me example for diadermic ointments?

Regards

Uma Prathyusha

Siriki Praveen Kumar's picture

neat clean and simply explained.,,.,.

helps everyone,.,.

Regards,

S. Praveen Kumar.

sirikipraveen11@gmail.com

Pharma warriors

Anonymous's picture

good 

plz give me ans of "how we calculate daily dose of ointment and amont of drug in systemic circulation

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