5.1 Pharmacognostical characterization of some selected medicinal plants <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
The word "Pharmacognosy" derives from the Greek words pharmakon (drug), and gnosis or knowledge. The term pharmacognosy was used for the first time by the Austrian physician Schmidt in 1811. Originally - during the 19th century and the beginning of the 20th century - pharmacognosy was used to define the branch of medicine or of commodity sciences ("Warenkunde" in German), which dealt with drugs in their crude, or unprepared, form. A "crude drug" means a dried unprepared natural material of plant, animal or mineral origin, which is used for medicine. The term drug derives from the Lower Saxon/Dutch "Droog", which means "dried" as in dried herbs (and has little to do with the modern pharmaceutical meaning of the term). The term "Pharmakognosie" and it discipline developed in German speaking areas of <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Europe - where it is a synonym of "Drogenkunde" ("science of the crude drugs").
The different fields within today's pharmacognosy include
- Ethnobotany or ethnopharmagocology; study of the traditional use of plants in the society. Ethnobotany refers to any use of the plants, whereas ethnopharmacology refers more specifically to the madical use of the plants.
- Phytochemistry, or natural product chemistry; a field closely related to organic chemistry, studying the chemical composition of living organisms. It is also closeöy connected to the process of finding new drug candidates from natural sources.
- Phytotherapy study of crude drugs, i.e. extracts from natural sources in medical use
Pharmacognosy includes the study of the proper horticulture, harvesting and uses of the raw medicinals found in nature. Its scope includes the identification or authentication of crude drugs (using macroscopical, microscopical, radiological or chemical methods), and their bio-pharmacological and clinical evaluations. Although today pharmacognosy is still taught in a small number of university pharmacy schools in US and in the UK, this subject is still obligatory within the pharmacy curricula in all universities of continental Europe.
Pharmacogonasy is mainly concerned with naturally occurring substances having a medicinal action. It also includes the study of other material used in pharmacy such as flavouring and suspending agents, disintegrants, filtering and support media and so on. It is closely related to both botany and plant chemistry.
Pharmacognosy has been generally pursued for utilitarian ends and may thus be called an applied science. It has played an important role in the development of the pure sciences, e.g. in descriptive botany, plant classification (taxonomy) and plant chemistry (phytochemistry). Chemical plant taxonomy, genetical studies, involving secondary metabolites are now attracting the attention of more and more botanist and chemists.
Vegetable drugs are usually arranged for study in one of the following five ways :-
1. Alphabetical : The drugs are arranged in alphabetical order using either Latin or English names .
2. Taxonomic : The drugs are arranged according to the plant from which they are obtained in phyla, orders, families, genera and species.
3. Morphological : Drugs are divided into different groups such as organized drugs which include root, wood, bark, flowers, fruits and leaves and unorganized drugs such as oil, fats, extracts and gums.
Pharmacological or therapeutic : Classification of drugs is according to the pharmacological action of their most important constituent.
4. Chemical : Drugs are classified according to their most important constituent that is alkaloids, volatile oils etc.
Pharmacy starting from medicine, separated and materia medica the science of material medicines describing collection, preparation and compounding emerged.
Even up to the begining of 20th century pharmacognosy was more a descriptive subject mainly of botanical science and consisted of identification of drugs both in entire and powdered condition and their history, commerce, collection, preparation and storage.
Period 1934-1960 :
The development of modern pharmacognosy book place later during the period 1934-1960 by simultaneous application of disciplines like organic chemistry, biochemistry, biosynthesis, pharmacology and modern methods and techniques of analytic chemistry including paper, thin layer and gas chromatography and spectrophotometry.
The substances from the plants were isolated, their structure elucidated and pharmacologically active constituents studied. The development was mainly due to following four events:
(i) Isolation of penicillin in 1928 by Fleming and large scale production in 1941 by Florey and Chain.
(ii) Isolation of reserpine from Rauwolfia roots and confirming its hypotensive and tranquillising properties.
(iii) Isolation of Vinca alkaloids especially vincristine and vinblastine. Vincristine was found useful in the treatment of leukeemia. These alkaloids have also anticancer properties.
(iv) Steroid hormones like progesterone were isolated by partial synthesis from diosgenin and other steroid saponins by Marker’s method. From progesterone by microbial reactions, cortisone and hydrocortisone are obtained.