Lec. 9
Dr. Saad Ali Ihsan
Methods Of Drug Evaluation
The aim of the drug evaluation is to identify and determine the quality
of the crude drug and detecting the nature of adulteration.
The evaluation of crude drug is essential because,
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There may be biochemical variations in the drug
There may be detoriation due to storage
Substitution and adulteration may be present as a result of
carelessness, ignorance etc
The crude drugs can be identified on the basis of their morphological,
histological, and chemical characters. The different techniques involved in
standardization of crude drugs are
Morphological and organoleptic evaluation
It refers to the evaluation of drugs by color, odor, taste, size, shape and
special features like texture
Microscopic evaluation
This method allows more detailed examination of a drug and their
identification by their known histological characters. Microscope by the
virtue of its property to magnify, permits minute sections under study to
enlarge so that, leaf constants, stomatal index, palisade ratio can be
determined.
Physical evaluation
These are rarely constant for crude drugs, but may help in evaluation with
reference to moisture content, specific gravity, density, optic rotation,
refractive index, melting point, viscosity, solubility etc.
Chemical evaluation
It compromises of different chemical test and assays. The isolation,
purification and identification of active constituents are the methods of
evaluation. Quantitative chemical test such as acid value, saponification
value etc are also covered under these techniques.
Biological evaluation
When the estimation of potency of crude drug or its preparations are done
by means of measuring its effect on living organisms like bacteria, fungal
growth, or animal tissue, it is known as biological effect of the drug,
compared to the standard drug.
By these methods a crude drug can be assessed and further clinical trial
can be recommended.
Spectroscopical evaluation.
(i) Ultra-violet & visible spectro photometry:
Measurement of light absorption by substances in the wavelength region
from 190 to 900nm.The region from 190 to 380 is known as the UV
region &from 380 to 900nm,the visible region of the spectrum.
Absorption in the UV-visible region arises from electronic transitions
within the molecule.
(ii) Infra-Red spectroscopy
I.R is the study of the reflected ,absorption or transmitted radian energy
in region of electromagnetic spectrum ranging from wave length ,0.8 to
500nm.I.R spectrum is divided in to three regions (a)near I.R 2500 TO
4000 cm-1 (b) mid I.R 4000 TO 400cm-1 (c) far I.R 400 to 20 cm-1 ,only
the mid region is referred to simply as infra red &widely used in the
analysis of drugs &pharmaceuticals.
(iii) Fluorescence analysis
Fluorescence means the substance in diluted acid solution. absorb light
over a specific range of wavelength &re-emission of absorbed light lasts
only while the substance is receiving the exciting rays .The drug
belladonna leaf &root ,aloes ,jalap show fluorescence in visible range
.The UV light obtained from mercury vapor lamp produce fluorescence
in many natural products .e.g cinchona gives purple blue fluorescence
,wild cherry gives mauve fluorescence.
(iv) Nuclear magnetic resonance spectroscopy (NMR):
NMR means absorption of radiofrequency radiation by substances held
in a magnetic field .NMR important tool for illustration of molecular
structure, specially the stereochemistry &configuration
(v) Mass spectrometry :
Is concerned with the electron ionization ,subsequent fragmentation of
molecules ,determination of the mass to charge ratio(m/e) & relative
abundances of ions which are produced. The application of mass
spectrometry is in determination of molecular weight of compounds.
(vi) X-ray diffraction:
Electromagnetic radiations of wave-lengths ,commonly generated by
passing high voltage current(about 10,000 volts)through a Coolidge
tube; they are able to penetrate most substances to some extent &to
affect a photographic plate
(vii) Radioimmuno assays (RIA):
The assay depends on the highly specific reaction of antibodies to
certain antigens.
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