In this term paper we will discuss about medicinal plants.
Man has been using herbs and plants products for combating diseases since times immemorial.
The Indian subcontinent is enriched by a variety of flora—both aromatic and medicinal plants. This is due to the wide diversity of climatic conditions in India ranging from deserts to swamplands. Numerous types of herbs have been well recognised and catalogued by botanists from the high ranges of the Himalayan tract up to the sea-shore of Kanyakumari. This extensive flora has been greatly utilised as a source of many drugs in the Indian traditional system of medicine.
In India, the earliest mention of the use of medicinal plants is to be found in the Rig-Veda which was written between 4500-1600 BCE.
The traditional system of medicine is so engrained in our culture that, even now 75% of the Indian population depend on this indigenous system for relief. With such a huge section of an ever-increasing population relying on herbal remedies, it is imperative that the plant products which have been in use for such a long time be scientifically supported for their efficacy.
The World Health Organization is now actively encouraging developing countries to use herbal medicine which they have been traditionally used for centuries. They have identified 3000 plants from the forests of India and other tropical countries which can be used as medicine. The active ingredients from these plants are worth nearly Rs. 2000 crores of rupees for the US market alone and nearly 8 times that for the world market.
Only with the scientific advancements in the fields of pharmacology and toxicology in the western hemisphere, has drug development based on natural products gained intensity in Europe and USA. The importance of such an investigation, in India was realised long back and the first systematic study with these aims was started by Sir Ramanath Chopra at Calcutta about 45 years back.
In the early stages, the science of medicine developed around those plants which had curative properties. A continued search for medicinal plants during the last several centuries has given rise to a long list of plants which are of great use in the treatment of diseases, and for promoting health. It can be stated, more or less truthfully, that every disease has a cure in a plant growing in nature. Recently, Moose has described a number of vegetable drugs that can be used as single drug remedies.
Drugs used in medicine today, are either obtained from nature or are of synthetic origin. Natural drugs are those obtained from plants, animals, microbes or minerals. Those obtained from plants and animals are called drugs of biological origin and are produced in the living cells of plants or animals.
Until now, only 6000 plant constituents have been isolated and studied. The flora on this earth, representing an inexhaustible source of medicinal plants, remains incompletely explored. This unexplored world provides the most challenging aspects of pharmaceutical and medical science to scientists in search of new and more potent drugs with marked therapeutic virtues and negligible side effects. During the last few decades, tremendous progress has been made in the study of phytochemicals.
Natural products, as a basis for new drugs, have great promise and it is gratifying to note that the World Health Organization have shown an abiding interest in plant-derived medicines, described in the folklore of various countries.
Plants have been one of the important sources of medicines since the dawn of human civilisation. For instance, the Chinese drug Mahung was in use for over 5000 years for the treatment of different types of fever and respiratory disorders. Cinchona sp was in use in Peru even in 1825, primarily for controlling malaria.
In spite of the tremendous development in the field of synthetic drugs and antibiotics during the 21st century, plants still contribute one of the major sources of drugs in modern as well as traditional medicine throughout the world. One-third of the world’s population treat themselves with traditional medicines.
Some of the compounds now commonly used in medicine were isolated from plant sources and used as early as in the 19th century. Examples are morphine (1803), quinine (1812), atropine (1831), papaverine (1848), cocaine (1860), digitoxin (1865), and pilocarpine (1875). Examples of some important compounds isolated in the 20th century include ergotmine (1518), labeline (1921), digoxin (1930), reserpine (1931), tubocurarine (1935), diosganin, vincristine (1961), and vimblastine (1963).
Plants are the only economic source of a number of well-established and important drugs. In addition, they are also the source of chemical intermediates needed for the production of some drugs.
As stated before, about 75% of the Indian population relies heavily on the use of herbal drugs for the treatment of diseases. The factors responsible for the continued and extensive use of herbal remedies in India are their effectiveness, easy availability, low cost, comparatively less toxic effects and the shortage of practitioners of modern medicine in rural areas. There is a growing appreciation in India, as in many other developing countries, of the need to make greater use of traditional remedies in order to be able to provide medicine for primary health care.
Although use of traditional remedies is advantageous, it does suffer some limitations. The main limitation is the lack of standardisation of raw materials, of processing methods and of the final products, dosage formulation, and the non-existence of criteria for quality control. Research has to be directed to the use of modern scientific methodology and techniques to standardise all these different steps and for quality control.
Before Independence, the production of plant-based drugs in India was confined mainly to cinchona and opium alkaloids, galenicals (i.e., medicine extracted from plants) and tinctures. In the last three decades, bulk production of plant drugs has become an important aspect of the Indian pharmaceutical industry.
Some of the drugs which are manufactured today include morphine, codeine, papaverine, thebaine, emetine, quinine quinidine, digoxin, caffeine, hyoscine, hyocyamine, atropine, xanthotoxin, sennosides, colchicines, berberine, vinblastine, vincristine and ergot alkaloids, papaine, nicotine, strychnine, brucine and pyrethroids.
In India, there are about 20 well-recognised manufacturers of herbal drugs, 140 medium or small-scale manufacturers, and about 1200 licensed small manufacturers on record, in addition to many vaidyas having small manufacturing facilities. The estimated current annual production of herbal drugs is around Rs.100 crores.
The demand for herbal remedies is ever-increasing. Herbal medicines represent an estimated $60-billion a year global market, about 20 per cent of the overall drug market, according to the United Nations agency. There are 1650 herbal formulations in the Indian market and 540 major plants involved in their formulations.
During the last two decades, over 3000 plants have been screened in India for their biological activities. As a result, a number of new drugs have been introduced in clinical practice and some are in the advance stages of clinical development.
There are well-documented scientific data on a good number of medicinal plants that have been investigated. In spite of all these efforts, very few drugs of plant origin would reach stage I of a clinical trial or gain enough creditability for clinical use by the practitioners of modern medicine.
This is because herbal drugs are sometimes considered dubious and its practitioners considered as quacks. The reasons are many.
Doubts have been raised on the use of herbal drugs for the following reasons:
1. Herbs of different origin are often known by the same popular name.
2. Plants growing in different climatic and seasonal conditions do not have identical chemical constituents or therapeutic effect.
3. The process of collection (fresh, shade or sun-dried), extraction, processing and storage of herbal medicines cause variation in potency and safety.
4. The lack of specific standards for herbal medicines in suitable dosage form creates difficulty in administration.
These shortcomings have delayed the integration of some of the better known Ayurvedic and Unani principles with the modern system of medicine.
But things are looking up with the gradual acceptance of Ayurvedic medicine. Further, detailed investigation on the mode of action of herbal drugs has revealed that they are involved in enzymatic, endocrine and immunomodulating functions. These have helped to widen their profile of activity and opened new vistas of therapeutic applications.
Illustrative Examples of Plants Used as Drugs:
The importance of plants as a source of useful anti-hypertensive drugs was supported by the isolation of reserpine from Rauwolfia serpentina, by Muller et al. in 1952. Veratrum alkaloids are other useful anti-hypertensive agents obtained from a plant source.
Allium sativum, zingiber officinale etc., have been mentioned to be useful in cardiovascular ailments in classical test books on ancient medicine.
Plant products have contributed several novel compounds possessing promising anti- tumour activity. For example, podophyllotoxin, alpha and beta pelatin were found to be capable of inflicting considerable damage on experimental tumours.
Various herbal medicines having a role in the treatment of diabetes have been described in classical Ayurvedic literature. Mention has also been made of different plant extracts used for anti-diabetic activity.
Aconitan A, isolated from Aconitum carmichaellii (family- Ranunculaceae) when administered i.p. to alloxan-induced hyperglycemic mice, exhibited blood sugar lowering action.
Quinquefolans A, B and C isolated from Panax quinquefolin (family- Arliaceae) had a hypoglycemic effect in normal mice. Quinquefolan A on i.p. administration alone, in alloxan-induced hyperglycemic mice produced a hypoglycemic effect.
Lists some plants used for central nervous system (CNS) drugs in Indian medicine ― Alstonia scholaris, Nardostachys jatamanasi, Apium graveoleus, Nymphaes lotus, Boerrharvia diffusa, Rauwolfia serpentine, Cardus diodara, Santalum album, Hydrocytyle asiatica, Vaneriana wallichii, Melia azadirachta and Vinca rosea.
Amongst the several plants investigated for anti-asthmatic effects, saponins isolated from Clerodendron serratum, Gardenia turgida, Albizzia lebbek and Solanum xanthocarpun were found to accord protection to sensitised guinea pigs against histamine as well as antigen (egg albumin) micro-aerosols. The protective effect of C. serratum saponin was found to be associated with the augmentation of anti-allergic activity in the lung tissues—lung extracts from the treated animals inhibited histamine and SRS-A responses on guinea pigs ileum to a greater extent and for a longer period as compared to the extracts from untreated control animals. Saponins from A. lebbek have also been demonstrated to modulate immune responses through synthesis of reagenic antibodies.
The alcoholic extract of Tylophora asthmatica has been reported to prevent egg albumin-induced anaphylaxis in guinea pigs and horse serum-induced bronchoconstriction in sensitised rat lung. Chewing of leaves of T. asthmatica for 6 days has been demonstrated to give protection to 71% cases of bronchial asthma on antigen challenge. The plant saponins from C. serratum and A. lebbek as well as the alkaloidal fraction of S. xanthocerpum and T. asthmatica have been shown to protect sensitised mast cells from degranulation on antigen shock, thus confirming the immuno-suppressive and membrane-stabilising effect. T. asthmatica as well as saponin of A. lebbek have also been found to potentiate bronchodilator beta-adrenergic activity, which is considered to be helpful for relieving bronchospasm in asthmatic patients. The anti-allergic action of O. sanctum has been found to be associated with significant production of IgE antibodies.
Search for a potent hypolipidaemic agent based on ancient insight following the Ayurvedic system, has been rewarding with the isolation of the oleoresin fraction from Commiphora mukul and Guggul having hypolipidaemic activity, comparable to Clofibrate with more favourable HDL-LDL cholestrol ratio. It also decreases platelet adhesiveness and increases fibrinolytic activity necessary for the prevention of myocardial infarction. It has been reported that the hypolipidaemic and cardio-protective effect of C. mukul in combination with Terminalia arjuna and Inula racemosa is comparable to Genfebrozil. The hypocholesterolaemic effect of Pterocarpus marsupium associated with hypoglycaemic activity, is of clinical significance as hypercholesterolaemia is often associated with diabetes.
Medicinal plants commonly included in Ayurveda for liver ailments have drawn much attention as there is no reliable hepato-protective drug available in modern medicine. The hepato-protective effect of some liver protectives like Picorrhiza kurrooa, T. cordifolia, Tephrosia purpurea against carbon tetrachloride and galactosamine-induced hepatic injury have been confirmed experimentally by various workers. In biliary ailments, plants such as Andrographis paniculata, Lyffa ectinata and Ficus hispida have been found to increase bile flow with reduction in serum bilirubin and SGPT levels. Phyllanthus niruri and Eclipta alba have been reported to eliminate hepatitis B surface antigen.
Plants have also been the source of anti-cancer compounds and anti-viral interferons. An interferon stimulator derived from Glycyrhiza glabra has been reported to give protection to patients with sub-acute hepatic failure known to be fatal in majority of cases.
The possibility of developing an herbal drug for the treatment of autoimmune diseases like multiple sclerosis and the dreaded AIDS cannot be ruled out.
Vegetables and Cancer:
Various systems of tribal medicine, not only of India, but also of China, Indonesia, Sri Lanka, Mexico, Malaysia, Philippines etc., have identified a number of food materials of vegetable origin which are not only anti-cancerous in nature but are also generally good for health.
The following are some of the plants traditionally used in this way:
1. Citrus aurantifolia
2. Allium cepalinn
3. Zingiber officinale
4. Anacardium occidentale
5. Coccinia grandis
6. Piper nigrum
7. Garcinia cambogia
8. Momordica charantia
9. Saccharum officinarum
10. Curcuma longa
11. Muring oleifera
12. Emblica officinalis
13. Tamarindus indica
14. Allium sativum, and
15. Piper betel.
Many of these have been used as food from times immemorial and perhaps have now given way to more fashionable vegetables.
The objective of producing inexpensive, potent and safe drugs of plant origin can be met to some extent by promoting compound formulations of plant medicines in their natural or semi-processed form as used in traditional medicine. Proper standardisation and dosage formulation in due consideration of the therapeutic-toxicity ratio will, however, be necessary with controlled clinical trials to prove their efficacy.
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