Scheme for Pharmacognostic Studies of a Crude Drug



A systematic study of a crude drug under pharmacognostic scheme involves it’s description on the following lines

  1. Official title, synonyms or vernacular names if any.
  2. Biological source and family.
  3. Geographical source or habitat.
  4. History and introduction of crude drug
  5. Cultivation, collection, processing for market and commerce in crude drug.
  6. Morphological or macroscopical characters.
  7. Microscopic or histological studies.
  8. Chemical constituents and qualitative chemical test.
  9. Pharmacological action, therapeutic and other pharmaceutical uses and pharmaceutical preparations of formulation.
  10. Commercial varieties, substitutes and adulteration.
  11. Quality control of crude drugs and phytopharmaceuticals derived from them.

A crude drug may have official or unofficial status. Unless otherwise indicated the official title of a crude drug is the title by which it appears in the pharmacopoeia or other official reference books. Official titles of the crude drugs are given birth in English and Latin. Synonyms are the frequency used alternative terms identical in sense to the official title of the crude drugs. This includes common or vernacular names for crude drugs.

The Latin name of the plant or animal with its family is called it’s botanical or Zoological source respectively. Biological source of crude drug also covers its nature, limits for the active constituents and any relative information affecting the quality of crude drug during processing or storage. The nature of the crude drug indicates whether it is the fresh or dried form eg: digitalis consists of dried leaves of Digitalis purpurea (Scrophulariaceae) dried at a temperature below 60°C immediately after collection and dried leaves should not contain more than 5% moisture.

The geographical source of a crude drug gives us information regarding the origin of drug, place and country where the crude drug is produced commercially on large scale. Cassie Angustifolia (Indian senna) is grown in and around Tinnevelly in Tamil Nadu of India.

The history of a crude drug reveals information about its introduction to mankind. It given us the information about the knowledge of a crude drug, it’s original place of growth and its introduction into modern medicine. History of some of the crude drugs like Rauwolfia roots, cinchona bark and opium are very interesting.

The cultivation technology for crude drug had to be studied systematically with reference to the selection of proper strains of seeds or germplasm, types of soil system, optimum climatic or ecological factors like light, temperature, rainfall, altitude and other factors like fertilizers, plant growth regulators, etc. The crude drugs are collected from the plants when they are rich in their active constituent content, which may be affected by the climatic conditions to a considerable extent. Drying of the plant material prior to packing is necessary to minimize moisture content of a crude drug to protect it from microbial contamination or undesired chemical reaction during storage. The crude Drugs can be dried either in sunlight or in shade or by use of artificial heat. In order to maintain high degree of quality in a crude Drug, it is necessary to store and preserve it properly. Light adversely affects quality of crude drugs which are highly coloured, whereas excessive moisture favours enzymatic activity and facilitates fungal growth.

The macroscopical or morphological description of a crude drug includes size, shape, nature of outer and inner surface, type of fracture and organoleptic characteristics like colour, odour, taste, consistency, etc. The quality of several aromatic drugs like clove and cardamom can be determined by smell.

Microscopical study of an organised drugs, either in entire or powdered form is one of the important aspects of its histological evaluation. The arrangement of tissue in transverse and longitudinal sections and types of cells and cell contents are revealed by suitable histological study of a crude drug with the aid of a microscope. Certain microscopical characteristics like stomata, trichomes, calcium oxalate crystal, starch grains, stone cells, fibres, vessels etc. Are important anatomical characteristic of organised drugs microscopical evaluation of crude drugs also involved linear measurement, study of surface preparation of level, quantitative microscopical aspects and chemo microscopy.

The utility of crude drugs is due to its Therapeutically active constituent. Clove contains volatile oil of which eugenol is the chief constituent. Most of the time, the crude drug also contains several other constituents which are inert Therapeutically. For example, caraway and many other umbelliferous fruits contain fixed oil and protein in addition to active principles which is volatile oil. Chemical tests are useful for qualitative chemical evaluation of crude drug. These tests are either general or specific and are usually performed for identification of the powdered drugs. Crude drugs like senna, Rhubarb, Cascara etc give positive anthraquinone test. Vitali’s test is performed for identification of tropane alkaloids of solanaceous drugs.

The pharmacological actions of active constituents of crude drugs and their Therapeutical or pharmaceutical uses from an integral part of a pharmacognostic scheme. Senna and Cascara are used as purgatives whereas digitalis and strophanthus are cardiotonic. Rauwolfia is used in the treatment of high blood pressure and insanity the activity being mainly because of the reserpine alkaloid. Some crude drugs and phytopharmaceuticals derived from plants are used as pharmaceutical necessities or flavouring and perfumery agents and they are devoid of any significant pharmacological action. For example, acacia and tragacanth are used as emulsifying agents honey as a sweetening agent, turmeric as a colouring agent and sandalwood oil for perfumes.

The study of difference species and varieties of medicinal or aromatic plants is of paramount importance especially when several closely related varieties are available commercially. In case of senna, cassia Angustifolia and cassia acutifoliate are the official drugs even through several other species of cassia such as C. Obovate, C. Auricular etc are widely grown. Several allied species of Strophanthus kombe are S. Hispidus, S.gratus, S. Emini, S. Sarmentosis etc. Some of which are equally important. The allied drugs of Rauwolfia serpentine are R. Vomitoria, R. Perakensis, R. Canescene, R. Micrantha and R. densiflora. The word ‘substitute’ itself is self-explanatory. Substitutes resemble the genuine drugs to a considerable extent in their morphology and type of chemical constituents. Substitutes resemble to a considerable extent to the genuine drugs in morphological behaviour and type of chemical constituent. Cinnamomum burmanii and C. loureirii are substitutes for C. Zeylanicum. Digitalis thapsi is used as substitute for D. purpurea.

Adulteration is debasement of an article and the adulterate resembles the genuine drug with respect to its morphological appearance and organoleptic characteristics. However, it is devoid of the active constituent which are present in the genuine drug. The adulteration of S. Nux-vomica such as S. Nux-blanda and S. potatorum do not contain strychnine. Cassia obovata or Dog senna is an adulterant of Indian senna.

Evaluation of a crude drugs means it’s identification and determination of its purity and quality. Quality control of a crude drug and its pharmaceuticals can be attempted by different methods of evaluation depending upon the morphological and microscopical studies of the crude drugs or their physical, chemical and biological behaviour. Systematic identification of crude drugs and their quality assurance from an integral part of drug description.