Introduction to Pharmacognosy PDF

# INTRODUCTION ## DEFINITION Pharmacognosy may be defined as a branch of bioscience (applied science), which deals with biological, biochemical and therapeutic features of crude drugs obtained from plants and animals and from mineral origin. In short, it is an objective study of crude drugs from na...

# INTRODUCTION ## DEFINITION Pharmacognosy may be defined as a branch of bioscience (applied science), which deals with biological, biochemical and therapeutic features of crude drugs obtained from plants and animals and from mineral origin. In short, it is an objective study of crude drugs from natural sources, which are treated scientifically, and it encompasses the knowledge of the history, distribution, cultivation, collection, processing for market and preservation. It is also the study of physical, chemical and structural characters and use of crude drugs. Pharmacognosy also includes study of other materials used in pharmacy such as suspending, disintegrating and flavouring agents, filtering aids, etc. and substances like antibiotics, allergens, hallucinogenic and poisonous plants, immunizing agents, etc. The word "Pharmacognosy" was coined by a German scientist, C.A. Seydler, at Halle, Germany, in 1815. (He coined the term pharmacognosy, while studying Sarsaparilla, in his work Analecta Pharmacognostica). The word pharmacognosy is derived from two Greek words Pharmacon meaning "a drug" and gnosis meaning "to acquire knowledge". ## HISTORY OF PHARMACOGNOSY The origin of pharmacognosy is somewhat obscure, for no one knows when crude drugs of animal and plant origin had been in use. The use of plants as sources of medicinal agents lies deep in the roots of antiquity. No one will ever know, what actually led primitive humans to select certain plant materials like roots, leaves, barks, fruits and even plant exudates for the treatment of various ailments and diseases. The three important basic needs of life-food, clothing and shelter-and a host of other useful products are supplied to humans by the plant kingdom. Nature has provided a complete storehouse of remedies to cure all ailments of humankind. Human beings are affected by more diseases than any other animal species. Therefore, the very dawn of civilization itself, humans would have been trying to alleviate their sufferings from injury and disease by using plants growing around them. Therefore in the past, almost all medicines used were mostly from the plants. Today, there is a vast store of knowledge concerning therapeutic properties of different plants. Therefore, the history of herbal medicines is as old as human civilization. The documents, many of which are of great antiquity, revealed that plants were used medicinally in China, India, Egypt and Greece, long before the beginning of the Christian era. Most of the medicinally active substances identified in the 19th and the 20th centuries were used in the form of crude extract. In China, many medicinal plants had been in use since 5000 BC. The oldest known book on herbs is Pen-t-Sao written by Emperor Shen Nung in 3000 BC. It contains 365 drugs, one for each day of the year. Our Indian population mostly depends on the Indian System of Medicine such as "Ayurveda", the ancient science of life and the Unani system. The well-known treatises in Ayurveda are the Charaka Samhita and the Sushruta Samhita. Galen was the first pharmacist, who had the number of pain-relieving materials including opium in his apothecary shop. In the 19th century, the term Materia Medica was used for the subject now known as "Pharmacognosy". The knowledge about the medicinal use of the plants was passed onto others by word of mouth. Later, as different civilizations developed, humans were able to communicate their knowledge and ideas, first by carving into stones or clay and later by writing on parchment or paper with the result that their knowledge became known to much later generations. Many of the crude drugs used during those civilizations are still used in the world today and to these the other plant materials are added continuously for the welfare of human beings. ## CLASSICAL PHARMACOGNOSY Religious beliefs have frequently influenced the use of plants, the most significant in Europe being the "Doctrine of Signatures" introduced by Paracelsus, a Swiss physician, who lived during the period 1493-1541. This "Doctrine of Signatures" had considerable influence on the use of plants in medicine throughout the world and its impact is still seen today. ## REASON FOR STUDYING PHARMACOGNOSY Whether the crude drugs were being used on a rational basis or not, there is no doubt that the development of medicine as a profession in the 12th century led to an increased trade in crude drugs which increased as the years went by. Trade and commerce have always provided opportunities for unscrupulous individuals to indulge in fraudulent activities; the trade in crude drugs was also not an exception to this. Thus came into existence, the practice of adulteration, for example, the drug opium was mixed (adulterated) with gum or latex of Lactuca. It was, therefore, felt necessary to prepare descriptions of plants and animals used for medicinal purposes and of the crude drugs obtained from them. One of the most outstanding works in this dirgstion was the publication of the four volumes Botanist with Hontry Trime of medicinal plants written by Robert Bently which remained the standard book of reference for many years. ## DEVELOPMENT OF MODERN PHARMACOGNOSY With the advent of European scientific methods, many of the reputed medicinal plants came under chemical scrutiny, leading to the isolation of active principles. Therefore many of the well-known medicinal plants were chemically analysed and their active principles were characterized. Soon after their isolation and characterization, these compounds, either in pure state or in the form of extracts, became part of Pharmacopoeias of several countries. Starting from the year 1815, there was rapid growth in the subject of pharmacognosy. This was due to development of various methods of isolation and characterization of active principles of crude drugs. Morphine was isolated from opium poppy (Papaver somniferum) by Segium in 1804 and was introduced as a Medicine in 1818. Similarly quinine was isolated by Pelletier in 1820 from cinchona and it was introduced as an antimalarial drug in 1825. Penicillin was isolated from a fungus Penicillium notatum by Alexander Flemming in 1922. Thus pharmacists started paying attention to the chemical constituents of different drugs which are used in medicine. In recent years, importance is being given to the preparation of semi-synthetic derivatives and synthetic substitutes of naturally occurring drugs. Modern pharmacognosy, therefore, grows with the growth of other sciences like chemistry, biochemistry, pharmacology, phytochemistry, etc. ## SCOPE AND IMPORTANCE OF PHARMACOGNOSY The scope of pharmacognosy includes a detailed study of 1. crude drugs obtained from plants, animals and minerals, and 2. other substances used by doctors and pharmacists like synthetic sutures and surgical dressings. Pharmacognosy is an applied science that has played a crucial role in the development of different disciplines of science. Its importance can be understood from the following. 1. It is concerned with an enormous variety of substances that are synthesized and elucidated by plants, animals, minerals and other substances and elucidation of these substancey involving extraction, purification and characterization, The technodos from natural sources is a significant contribution to the advancement of natural and physical sciences. 2. Pharmacognosy forms an important link between pharmacology and medicine chemistry. As a result of rapid development of phytochemistry and pharmacological testing methods in recent years, new plant drugs are produced in medicine as purified phytochemicals rather than in the form of traditional or galenical preparations. 3. The knowledge of pharmacology through pharmacognosy is very essential for understanding the action of drugs on animals and the human system. 4. Pharmacognosy forms the infrastructure, on which depends evolution of novel medicines as it is seen that several crude drugs are utilized for preparation of galenicals or a sources of therapeutically significant substances that cannot be synthesized economically. 5. The crude drugs also provide essential intermediates for final synthesis of active compounds. 6. It provides a system wherein active principles of crude drugs derived from natural sources could be dispensed, formulated and manufactured in dosage forms, acceptable to allopathic system of Medicine. 7. Pharmacognosy forms a vital link between Ayurveda and Allopathic systems of medicine. 8. In a nutshell, pharmacognosy forms an important bridge between the pharmaceuticals and basic sciences. # COLLECTION AND PROCESSING OF CRUDE DRUGS Crude drugs need to undergo suitable preparation for being marketed. The reasons for such preparation of crude drugs are as follows: * To stabilize them in transport and storage. * To ensure the absence of foreign organic matter and substitutes. * Market preparation of crude drugs also takes care of pharmaceutical values. The following methods are used in the preparation and processing of crude drugs. * Collection and harvesting of crude drugs * Drying * Garbling * Packing prior to marketing to meet the standard pharmacopoeial requirements ## COLLECTION AND HARVESTING Harvesting of medicinal plants needs proper planning. Plant materials, animal products and other forms from which crude drugs are extracted are collected in such a way that the parts must contain maximum concentration of the active constituents. Wild plants have high concentration, and collection of wild plants has a number of drawbacks—it is unscientific, labour-oriented and undependable. Collection by untrained collectors leads to the danger of wrong identification and collection of poisonous crude drugs. ## METHODS OF PLANT COLLECTION The collection process is initiated usually when plant collectors are free and when there is demand for crude drugs. Generally, the existing environmental conditions are not taken into consideration. The following are some of the important points to be borne in mind during collection: * Underground parts like roots, corms, bulbs, rhizomes, tubers, etc. should be collected at the end of flowering and fruiting, that is, during July-August and March-April. * All the underground parts collected should be cleaned and dried in shade or ovens at 30°C, e.g., Gloriosa, garlic, etc. * In case these parts are collected during summer, their survival and regeneration are affected during the next growing season. * Fruits and flowers should be collected individually only after maturity. * Annual stems should be cut 5-10 cm above the ground, after the plant has begun to flower. * Leaves are collected at a young stage, as the leaves usually contain a high content of chemical constituents during this stage, e.g., tulsi, pudina, etc. * Specific parts of flowers like petals (lotus), whole flowers (Vinca) and flower buds (clove) are collected separately. * Fruits and berries are harvested in early autumn, e.g., cardamom. * Barks are collected in spring or early summer when the cambium is very active and it is easy to detach them from the stem during this season. * Sap from tree is collected in spring as it rises, e.g, silver birch. * Milky latex is collected by squeezing the stems over a bowl using gloves e.g., Taraxacum. ## METHODS OF HARVESTING Harvesting is an important operation, as it reflects upon the economic use of the crude drugs. The following are the important do's during harvesting: * Skilled workers should do this operation. * Selective collection of drugs is very essential. * Hand-picking is done for leaves, fruits, etc. * Mechanical devices like diggers or lifters should be used for underground drugs. * All aerial parts are harvested by binders. * Seed strippers are used for flowers, seeds and small fruits. * Cochineal insects are collected from branches of cacti by brushing. * Mowers are used for peppermint. * Sometimes reaping machines are also used for harvesting. ## DRYING Proper drying preserves the drugs for a long time and also maintains better pharmaceutical value. The purpose of drying is to remove sufficient amount of moisture, so as to get good quality of crude drugs. In addition, drying helps the drugs to resist microbial growth and also helps in proper grinding of the drugs. Before drying, special methods like fermentation, slicing and cutting the materials into small pieces are utilized to enhance better drying. ## METHODS OF DRYING Depending upon the type of chemical compounds present in the drugs, the following two methods of drying may be practiced—natural drying or sun drying and artificial drying. 1. **Natural drying** In order to retain the natural colour as in clove, senna and also the volatile principles of the drug (e.g., peppermint), the crude drugs are dried in the shade. Gums, resins and some fruits and seeds can be dried directly in sunlight. 2. **Artificial drying** It includes oven-drying (tray-drying), vacuum-drying and spray-drying. * **Oven-drying** In this method hot air is used to dry the drugs, e.g., cinchona bark, tea, etc. * **Vacuum-drying** Drugs that are sensitive to high temperature are dried by this process, e.g., tannic acid and digitalis leaves. * **Spray-drying** Drugs that are highly sensitive to atmospheric conditions and also to vacuum-drying are dried by this process. Spray-dryers are used for quick drying of drugs, e.g., papaya latex, pectin, etc. * **De-humidifying** In this method herbs are dried with the help of an instrument called dehumidifier. The dehumidifier is placed in a sealed small room, in which the herbs are hung in loose bunches or placed on mesh trays, to suck water out of the plants. In this process herbs will dry very quickly as no heat is used. It is an expensive method, but very effective. ## GARBLING The process of removal of dirt and foreign organic materials from the drug is called garbling or dressing. The unwanted stems, bark, rootlets, iron, etc., should be removed to get better quality. ## PACKING The following aspects are to be considered while packing the drugs. * Morphological and chemical nature of drugs. * Its ultimate use. * Climatic conditions during transportation and storage. The materials used for packing different drugs are as follows: * Goatskin is used for packing Aloe. * Colophony and balsam of Tolu are packed in kerosene tins. * Asafoetida is packed in closed containers. * Senna and Vinca leaves are pressed and wrapped. * Roots and seeds can be packed in gunny bags. ## STORAGE OF DRUGS A number of drugs absorb moisture during their storage and become susceptible to microbial growth. The excessive moisture also facilitates enzymatic reactions resulting in decomposition of active constituents, e.g., ergot. Exposure of drugs directly to sunlight also causes destruction of active chemical compounds. Shape also plays a very important role in preserving the crude drugs. Colophony is preserved well when it is in entire form, but if stored in powdered form it gets oxidized. The fixed oil in the powdered ergot becomes rancid on storage. Therefore, to maintain a good quality, ergot drug should be defatted with lipid solvent prior to storage. Lard should be preserved against rancidity by adding siam benzoin. In order to protect the drugs from destruction of atmospheric oxygen, they must be stored in air-tight containers. For certain drugs like shark-liver oil, papain, etc., they are stored in containers where air is replaced by an inert gas like nitrogen. Protection and preservation of drugs against insect and hydrocyanic acid. As high temperature decomposes the drug during storage, drugs should be stored at a very low temperature. Costly phytopharmaceuticals are preserved at refrigerated temperature in closed containers. Wooden boxes and paper bags should not be used for storage of drugs. ## PROCESSING OF CRUDE DRUGS Medicinal plants must be treated and modified in such a way that its specific curative substance can be put into practice. The active principles of the medicinal plants either individually or in groups can have a specific action on our organs. Different methods are followed to extract these substances from medicinal plants. ## METHODS OF PREPARATION The medicinal plants are subjected to the following processes for the preparation of different herbal dosage forms. * Decoction * Maceration * Infusion * Juice extraction **Decoction** This method is used for plants whose active principles are not soluble in standing cold or boiling hot water or difficult to extract. Therefore the crude drug is boiled in a specified amount of water for a defined time, cooled and filtered to get the decotion. A decoction is generally prepared using woody parts like roots, rhizomes, barks and berries, but sometimes leaves and flowers may also be included. For decotion, fresh materials should be sliced or cut into small pieces, while dried crude drugs should either be powdered or well-bruised. **Maceration** This process is carried out for drugs whose active principles take very long time to dissolve in cold water, without heating. As a result their active constituents will be released in cold water, e.g., mucilage. **Infusion** The dilute solutions of the readily soluble constitutents of crude drugs are called infusions. An infusion is the simplest way to prepare the most delicate aerial parts of plants especially leaves and flowers or fruits for use as a medicine or as a revitalizing or relaxing drink. It is usually prepared using either a single herb or a combinations of herbs and may be drunk cold or hot. There are two types of infusions, namely, cold infusions and hot infusions. * **Cold infusions** When the active principles of the drugs are volatile in nature or sensitive to heat treatment, cold infusions are preferred. These are prepared by immersing the drug in cold water for some time. During this time all the active principles present will be released into the water without heating, e.g., tamarind. * **Hot infusions** These are made by pouring boiling water over the herb or herbal parts and keeping the infusion in a covered container for 5-10 minutes to dissolve and then filtered. Herbal teas are generally prepared in this way, e.g., Chebula, tea, etc. **Juice extraction** Extraction of juice is similar to preparing decoction of medicinal plants. ==End of OCR==