Evaluation of a drug helps identify a drug and determine its purity. The need for evaluation is due to the biochemical variations in the drug, its effect on treatment and storage, and the presence of adulterants and substitutes.
Methods that are currently employed in evaluating drugs are physical, chemical, biological, organoleptic, and microscopic.
Physical Evaluation of Crude Drugs
The physical evaluation of the crude drugs is done with the help of physical characteristics such as
- Solubility
- Optical rotation
- Refractive index
- Specific gravity
- Melting point
- Viscosity
- Fiber elasticity
- Water content
Chemical Evaluation of Crude Drugs
The chemical evaluation of crude drugs consists of qualitative and quantitative methods. There also are instrumental analysis and chemical assays.
Qualitative Chemical tests
Isolation, purification, and identification of various phytoconstituents form the qualitative evaluation of crude drugs. Alkaloids, tannins, glycosides, etc are identified by these steps. The identification test will be different for each type of constituent.
Specific tests
- Van Urk test for ergot alkaloids
- Vitali-morin test for tropane alkaloids
- Murexide test for purine alkaloids
- Iodine for starch
Detection of adulteration
- Halphen’s test detects cottonseed oil
- Fiehes test for honey
- Colophony in resins, waxes, and balsams is identified with copper acetate
- Baudouin’s test detects sesame oil in olive oil
- Acetic and nitric acids are used for detecting Gurjun balsam in copaiba
Quantitative Evaluation
Quantitative tests include tests for,
- Acid value for resins and balsams
- Saponification value of balsam
- Ester value of volatile oils and balsam
- Acetyl value of volatile oils
Chemical Assays
Chemical assays help determine the total content of the active constituents. It also helps determine the presence or absence of an inferior drug so that necessary steps may be taken for a complete substitution of the constituent. A few examples of chemical assays are given below.
- Total alkaloid content in belladonna
- Total alkaloid and nonphenolic alkaloid in ipecacuanha
- Alkaloid strychnine in nux vomica
- Resin in jalap
- Vitamins in cod liver oil
Instrumental Analysis
Here, the chemical groups are analyzed using chromatographic methods and spectroscopic methods. Paper chromatography, TLC, gas chromatography, HPTLC, HP Liquid chromatography, etc are the common chromatographic methods used.
Different methods of spectroscopy include visible spectroscopy, UV spectroscopy, infrared spectroscopy, mass spectroscopy, nuclear magnetic spectroscopy, etc.
Biological Evaluation of Crude Drugs
The biological evaluation of crude drugs is done to determine their toxicity, potency, and pharmacological activity. This is a far better method of evaluation than chemical and physical evaluation. Biological evaluation helps conclude its biological activity more precisely.
Bioassay or biological evaluation should be simple but must have access to a large number of tests and screening. Bioassay can be tissue or organ method, symptomatic or toxic. While isolated tissue or organs are used for the first type of evaluation, different types of animals are used for symptomatic and toxic evaluation.
In biological evaluation, the required amount of drug is determined for the definite effect in the chosen animals, isolated tissue, or organs under standard conditions. Certain methods use reference standards to reduce possible errors.
Toxicity studies on animals help decide the effective dose and lethal dose of the drugs. Mice, guinea pigs, young domestic chickens, pigeons, cats, worms, rabbits, etc are commonly used animals for the biological evaluation of crude drugs. Animals are chosen according to the drug and its target.
- Glycosides from Digitalis are tried in the pigeon bloodstream to observe any lethal effects.
- Rabbits are used for checking drugs that affect the eyes.
- The effects of Ergot are tried in rabbits in their cock combs, intestine, or uterus.
- Guinea pigs are mainly used to study the oxytocic effects of vasopressin.
- Oxytocic drugs are injected into young chickens to study their effects on blood pressure.
- Mydriartic effects of drugs are studied in cat’s eyes.
- Cardiac and gastrointestinal effects of drugs are conducted in dogs.
- Anthelmintic drugs are tried in worms.
Microbiological assays determine the effects of drugs on microbes, helping in the identification of antimicrobial drugs. Agar well diffusion, disc diffusion, turbidimetric, etc are the microbiological assay methods. Bacterial yeast molds are used to study vitamins.
Organoleptic Evaluation of Crude Drugs
The evaluation of crude drugs based on the sensory organs is called organoleptic evaluation. The drugs are assessed based on their color, size, shape, odor, texture, taste, etc. It is the simplest form of drug evaluation and the manual process as well.
Such analyses are useful for distinguishing drugs having similar appearances. In those cases, the taste, odor, or texture are assessed to separate one from the other.
- Talka gum is brown or colorless while Acacia gum is white or yellow.
- Mangosteen fruit has a darker rind with radiate stigmas in a wedge shape.
- Bloodroot has a dark reddish-brown color while Hydrastis is yellow.
- Ginger and capsicum have their distinct odor.
- Chirata and gentian have a bitter taste.
- Indian and Alexandrian senna are morphologically different.
- Cinnamon has a dark brown color
- Volatile oil drugs have a distinctive aroma
- Capsicum has a pungent taste while licorice is sweet
- Shape as a distinguishing feature is seen in the wavy Rauwolfia, the Ovoid tears in Acacia, and the disc shape of Nuxvomica
- The small size of umbelliferous fruits
- The silky texture of Nux vomica
- Cinchona and Quassia have fractured surface
- The general appearance is considered to find the percentage of seeds in colocynth and stalks in clove
Microscopic Evaluation of Crude Drugs
Microscopic evaluation is conducted on small fragments, powdered drugs, and other minute parts of plants that cannot be subject to physical evaluation methods. This is part of the initial identification methods.
This is possible due to the unique anatomical characteristics of plant parts. The cell wall, presence or absence of stomata, cell contents, starch grains, calcium oxalate crystals, lignified or scelrenchymatous cells, etc are all part of this process.
This initial examination helps identify the parts and any possible contamination. For eg., clove stalks will have calcium oxalate crystals and sclereids in them but cloves do not have these two. Another example is the presence of sclerenchyma in Rauwolfia serpentine which will be absent in other species which are adulterants.
Similarly, other drugs and their adulterants are identified with the help of microscopic examination, based on the presence or absence of such features.
References
- Evaluation of Crude Drugs
- Shah, Biren N, Avinash Seth. (2010). Textbook of Pharmacognosy and Phytochemistry. Elsevier.
- https://www.pharmacy180.com/article/biological-evaluation-74/
- Pharmacognosy & Phytochemistry – I
Additional Reading
- Classification of Crude Drugs in Pharmacognosy
- Physical Evaluation of Crude Drugs
