PCG 302: Phytoevaluation (2 Units)
What is Pharmacopoeia?
Pharmacopoeia, otherwise known as formularies, are books that contain the
standards for drugs and other related substances. The word “pharmacopoeia” is
derived from the Greek words ‘pharmacon’ meaning ‘drug’ and ‘poieo’ means
‘make’. Literally it means that it is a list of medicinal substances, crude drugs
and formulae for making preparations from them. Pharmacopoeia contain a list
of drugs and other related substances with regards to the following details:
Source
Descriptions
Standards,
Tests,
Formulae for preparing the drug
Action and uses, doses,
Storage conditions etc.
It is under the authority of the governments of the respective countries that
these books are prepared and they are subject to revision from time to time. It is
revised over time because once new information is established, it should be
included as soon as possible. Sometimes new editions of the book might omit
older monographs and introduce newer ones. The expert opinion of medical
practitioners, teachers and pharmaceutical manufacturers are obtained for the
preparation of these books.
Pharmacopoeial requirements for crude
drugs
Pharmacopoeial requirements are a set of standards used to evaluate crude
drugs either in their raw form or powdered form. The whole process of evaluation
is meant to determine the quality and purity of the crude drug. The process is
carried out by comparing the unknown samples with known monographs that are
already established and written in Pharmacopoeia.
1. Organoleptic Evaluation
The organoleptic evaluation involves using the sense organs to study crude
drugs. This includes its external morphology, colour, taste and odour.
There are two organoleptic characters to consider:
a. Morphological characters: It includes organised and unorganised portion of
the plant. Organised parts includes stem, roots, fruits, flowers, seeds,
leaves, herbs, etc. Unorganised parts includes resin, gums, latex, etc.
b. Sensory characters: Colour, odour and taste are sensory characters of the
drugs. e.g: clove and cinnamom gives characteristic odour ginger and
capsicum gives pungent taste, glycyrrhiza and honey are sweet.
2. Microscopical Evaluation
The known histological characteristics of crude drugs are used in evaluating
them microscopically. The shape, size, relative position of cells and tissues,
chemical nature of cell wall and cell content are determined. There are certain
constants that are used in microscopical evaluations:
a. Stomatal Number: This is the average number of stomata per square mm
of the epidermis.
b. Stomatal Index: It is the percentage proportion of the number of stomata
to the number of epidermal cells of a leaf.
S
Stomatal Index = × 100
E+S
Where: S = number of stomata per unit area and E= number of
epidermal cells in the same area
c. Vein-islet number: This is the number of vein islets per sq. mm of the leaf
surface between midrib and the margin.
d. Vein termination number: is the number of veinlet terminations per sq.
mm of the leaf surface between midrib and margin.
e. Palisade ratio: is the average number of palisade cells beneath each
epidermal cell.
Examples of established pharmacopoeial standards for some crude drugs are:
Atropa beladona
Leaf Constant Value
Stomatal number 77–115
Stomatal index 20.2–23
Vein termination number 6.3–10.3
Palisade ratio 6–10
Digitali purpurea
Leaf Constant Value
Vein islet number 2–5.5
Palisade ratio 3.7–4.2
3. Physical Evaluation
The physical parameters considered in the evaluation of crude drugs includes:
a. Moisture content: The moisture content is determined by heating a drug at
about 105°C in an oven to a constant weight. However, it must be noted
that excessive moisture content deteriorates the quality of drug by
activating enzymes and growth of micro-organisms. Example, starch
should contain not more than 15% moisture
b. Ash Content: The residue remaining after the incineration of drug is the
ash content of the drug.
- Total ash value is determined at around 450°C which may contain
carbonates, phosphates, oxides, silicates and silica. Sulphated ash is
determined by treating drug with dilute sulphuric acid at around 600°C.
- Acid insoluble ash: When total ash is treated with dilute hydrochloric
acid, the acid insoluble ash is determined. It is the resulting inorganic
residue.
Drug Total ash % w/w Acid insoluble ash %
Clove 7 0.75
Cannabis 15 5
c. Rf Value: Rf means flow ratio. It is simply the ratio of distance covered by
the solute to the distance covered by the solvent in chromatography.
d. Refractive index Refractive index is the ratio of velocity of light in vacuum
to velocity of light in the substance.
Velocity of light ∈vacuum
Refractive Index =
Velocity of light ∈substance
The value of refractive index is constant and very useful for the
standardization of Volatile and fixed oils. It is measured by refractometer.
e.g: clove oil has refractive index 1.530-1.531
e. Extractive Value: Crude drug extract is obtained by the process of
maceration or continuous extraction by soxhlet extractor. The solvent
used for the extraction dissolves the phytochemicals present in crude
drugs like alkaloids, glycosides, tannins, resins, etc. Solvents like alchohol,
water, ether, etc are used for extraction.
f. Volatile oil content: Volatile oil is obtained from crude drugs using
clevenger apparatus in the laboratory. Ether is used as solvent for
obtaining volatile oils.
g. Melting Point is the temperature required to melt down the drug. Melting
points are sharp and constant in pure chemicals and phytochemicals.
h. Viscosity is the property of a liquid to resist its flow. It is measured by
using Ostwald viscometer.
Read on the following: Optical Rotation, Foreign Organic Matter, Clevenger
Aparatus and Ostwald Viscometer,
4. Chemical Evaluation
Chemical evaluation of crude drugs involves isolation, purification, identification,
chemical tests and chemical assays. Phytochemical screening is the qualitative
chemical evaluation. It includes test for phytochemicals like carbohydrate,
protein, alkaloids, glycosides, tannins, etc. Quantitative chemical tests includes
acid value, saponification value, ester value, etc Examples of tests include:
Tannic acid test for alkaloids and Borntrager’s test for glycosides.
5. Biological Evaluation
Biological evaluation is done to determine effect & potency of drug in living
organisms, animal preparations or isolated living tissue. It is also known as
bioassay. It can evaluate both pharmacological activity and toxicological activity
of a drug. Biological evaluation is done to confirm the test after physical and
chemical test. Biological evaluation can be:
i. Pre-clinical testing: Testing in laboratory animals like mouse, rat, pig, dog,
etc.
ii. Clinical testing: Testing in human volunteers
