Specialist pharmacist
Ghada Ali AL-Hussiany
Pharmacognosy
Lecture ( 9 )
Drug evaluation
Evaluation of drug means confirmation &comply of drug &determination of its quality,purity &detection of nature of adulteration.
Evaluation of crude drug is necessary because of three reasons:
1-biochemical variation in the drug.
2-deterioration due to treatment &storage
3-substitution &adulterationituent present ,as a result of carelessness, in the
Evaluation include ;method of estimating active constitutent present in the crude drug ,in addition to its morphological µscopic analysis,its possible to perform physical evaluation of crude drug ,the biological behavior of crude drug ,extracts, determine pharmacological evaluation.
The crude drugs can be identify by:
1-Morphological or organoleptic evaluation:
It refers to evaluation of drugs by colour ,odour ,taste ,size ,shape&special features like touch texture.....etc
Organoleptic evaluation means conclusion from the study of the result .
The general appearance of the lot of a crude drug indicates whether its likely to comply with standard. e.g fractured surface in cinchona &cascara are important characteristics .
Aromatic odour of fruit &sweet taste of liquorice are important in evaluation ,disc –shaped structure of nux-vomica ,conical shape of aconite are important in diagnosis .
The wave shape of rouwolfia &ginger ,brown colour of cinnamon , odour &taste of spice drug like black pepper ,nut meg ,caraway …..etc are also important diagnostic organoleptic charactorstics.
2-Microscopic evaluation (histological)
It can be used to identify the organized drug in powdered form by their histological characters,various reagents &stains can be used to distinguish cellular structure ,this evaluation also covers study of the constituents by application of chemical method to small quantities of powdered drug (called chemo microscopy).
3-chemical evaluation
It consist of different chemical tests& chemical assay .The isolation, purification & identification of active constituents are chemical methods of evaluation.
Quantitative chemical test like acid value, saponification value , sulphated ash ,ester value ,acetyl value are useful in evaluation resins,balsams &volatile oil….etc,
Qualitative chemical tests are useful in detection of adulteration ,these specific test like balsams &waxes is detected by copper acetate murexide test for purine bases……etc,
The purity of crude drugs is detect by quantitative estimation of active constituents present in drugs for example titrimetric estimation to estimate of alkaloid in crude drugs ,ester& aldhyde content of volatile oils ….etc
The method may be useful in determining single active constituent or the group of related constituents present in the same drug.
4-Physical evaluation
In this evaluation physical standards are to be determined for drugs which is constant for crude drugs ,but may help in evaluation ,these are :
· Moisture content; is determined by heating a drug at 1050C in the oven to constant weight.
· Viscosity of liquid ;is constant at a given temperature & is an index of composition
· Melting point ;it is one of the parameters to judge the purity of crude drugs .
· Solubility; the presence of adulterant in a drug could be indicated by solubility e.g the glycosides are extract with alcohol &water while aglycone are soluble in non polar solvent like benzene.
· Optical rotation ; is determined at 250C using sodium lamp as the source of light .plane of polarized light may be rotated towards right (dextro rotatory ) or towards left (levo rotatory) .
· Refractive index :is the ratio of the velocity of light in vacuum to its velocity in the substance .It s constant for purity drugs at constant temperature.
· Ash values & extractives; ash which is simply represents inorganic salts , naturally occurring in drug or adhering to it as a form of adulteration like sand , oil , calcium oxalate ,chalk powder. Extractives ;various solvents are used for determination of extractives , the solvent used for extraction is in a position to dissolve appreciable quantities of substance
· Volatile oil content ,aromatic drugs is due to their odorous i:e volatile oil content e.g caraway ,dill ,clove , cardamom seed .
· Foreign organic matter ;the limit for foreign organic matter is mentioned for natural drugs of vegetable origin
5-Biological evaluation
It is known also as bioassay ,means the crude drug or sample tested capable of producing biological effect as that of the standard preparation; the activity is represented in units known international unite (I.U). i:e the specific biological activity contained in each I.U e.g Digitalis contained 76mg of standard preparation in one I.U. Bioassay method are mainly three type: a-toxic b-symptomatic &c-tissue methods. Toxic &symptomatic ,the animals are used ,whereas tissue method used isolated organ or tissue.
Spectro photometric methods
(i)Ultra-violet &visible specro photometry:
Measurement of light absorption by substancesin 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 vapour 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.