From his first awakening, man has sought to fight and control diseases, and turned to nature for inspiration and guidance. During thousands of years of early human existence, many natural materials by instinct or intuition or trial and error got in use for combating human ailments. Thus, traditional systems of medicines such as Ayurveda, Unani, Siddha, and Homoeopathy lean heavily on natural products, derived from higher plants, microbes or animals. Traditional healers have left voluminous treatises from which many formulations have been taken which are currently in use. None the less, as the preparations of drugs has become commercial, an urgent need has arisen to have a quality control check on the various formulations to assure the consumer a supply of effacious drugs.
Traditional healing arts are generally based on a single medicinal plant drug or multiple drug. In such circumstances, the medicinal plant used for the preparations of a drug should be authentic and genuine. The formulae used in some Ayurveda and Siddha drug preparations are taken even from palm-leaf manuscripts. The consumers should be assured of the quality of the drugs. Hence, scientific methods of standardization are needed to confirm the authenticity of medicinal plants used in the preparation of a drug. To standardize or to evaluate a crude drug means to identify it and to determine its quality and purity. The identification of a crude drug can be established by actual collection of the drug from a plant that has been positively identified. Quality refers to the intrinsic value of the drug. ie. the amount of medicinal principles or active constituents present.
The evaluation or standardization of a crude drug involves a number of methods that may be classified as:
a) Organoleptic
b) Phytochemical
c) Pharmacognostic methods
d) Pharmacologic
Organoleptic methods
Organoleptic refers to the evaluation by means of the macroscopic appearance of the drug, its odour, taste and the 'feel' of the drug to touch. For example, the four common Ocimum sanctum (Krishna Tulasi), Ocimum Gratissimum Linn. (Rama Tulsi), Ocimum Basillicum Linn. (Tireneetru Pachilai) and Ocimum canum sims. (Nay Tulasi) can be very easily differentiated by looking into the size and colour of the leaves and also by odour.
Pharmacognostic methods
Pharmacognosy is an applied science, which deals with botanical, physico-chemical and economical features of the crude drugs of animal and plant origin.
In a large number of cases, botanically different plant has now come to be used for same drug in different places and sometimes even in the same locality. A different plant, more easily and cheaply available is used in the place or even in addition to the correct plant. The variants and substitutes are sometimes different species of the same genus or they may belong to different families or even to different classes. For example, the morphological features of the root of Vinca rosea (Fam.Apocynaceae) called 'nithyakalyani' in Tamil and that of Prosophis julifera (Fam. Leguminosae) are similar. Hence, the roots of Vinca rosea, which are used for curing cancer, are adulterated with the roots of Prosophis juliphera which do not cure cancer. Similarly, Trianthema portulacastrum Linn. (Fam.Ficoidaceae) closely resembles Boerhaavia diffusa ( Fam.Nyctaginaceae) in appearance. Hence, the former is often adulterated with the latter in the market.
Another matter, which commonly produces confusion, is the inconsistency in the use of vernacular names of the plants. Different localities have different vernacular names for the same plant or sometimes the same name for more than one plant. Thus it become difficult to get at the correct plant with the help of vernacular names. For example, The vernacular name :koranti is used to denote both Salacia reticulata wight, (Fam.Ficoidaceae) are commonly known as 'Vellaisharunai' and 'Vattasharunai' respectively in Tamil. Both the plants are called 'Punarnavi' in Sanskrit. Hence, there is every possibility of adulteration of one species with another because of the confusion in vernacular names.
Hence, a systematic determination of pharmacognostical characters such as
1) anatomical studies of the fresh root, stem and leaf
2) flurescene analysis
3) Physico chemical characters such as ash values, loss of weight on drying, residue on ignition, and extractive values will be very much useful in the correct identification and standardization of the crude drug.
Phytochemical methods
Phytochemistry has developed in recent years as a distinct discipline somewhere in between natural product organic chemistry and plant biochemistry and is closely related to both.
It concerned with the enormous variety of organic substances that are accumulated by plants and deals with the chemical structures of these substance, their synthesis, turnover and metabolism, their natural contribution and their biological function.
Quality refers to the intrinsic value of the drug, i.e. the amount of medicinal principles present. The active constituents are carbohydrates, glycosides, tannins, lipids, flavonoids, coumarins, phenolic compounds, volatile oils, resins, steroids, alkaloids, peptide hormones, enzymes, and other proteins, vitamins, antibiotics, allergens and others.
A high grade of quality in a drug is of primary importance and efforts should be made to obtain and maintain this high quality in the plant drug.
Hence, qualitative and quantitative estimation of the phytochemical constituents will be very much useful in the standardization of crude drugs. In addition, the various chromatographic techniques such as thin layer, paper, column and HPLC techniques can be employed for the isolation of the particular phytochemical. Using modern spectroscopic techniques such as UV, I.R., H-NMR, C-NMR, Mass, ORD and CD, the new compound can be characterized and their structures determined. The presence of a particular class of chemical compound in the various species of the family of plants can be used as a chemotaxonomical marker. For many drugs, the chemical assay represents the best method of determining official potency.
-- The author is with Department of Chemistry, Manonmanian Sundaranar University, Tirunelveli