Pharmacognosy PDF

# **Pharmacognosy** ## **Definition** The word “Pharmacognosy” derived from the Greek word "Pharmakon" means a drug, or medicine. "Gignosco" means to acquire knowledge. Pharmacognosy is the study of drug derived from natural sources. This field encompasses the study of the physical, chemical, bioche...

# **Pharmacognosy** ## **Definition** The word “Pharmacognosy” derived from the Greek word "Pharmakon" means a drug, or medicine. "Gignosco" means to acquire knowledge. Pharmacognosy is the study of drug derived from natural sources. This field encompasses the study of the physical, chemical, biochemical and biological properties of drugs, as well as the search for new drugs from natural sources. ## **Crude Drugs** * The term crude drug generally applies to the products from plants, animal, and mineral origin found in a raw form. They are used in the treatment of various disorders and ailments of human beings. * The most important natural sources of drugs are higher plants, microbes, animals, and marine organisms. Some useful products are obtained from minerals that are both organic and inorganic in nature. ## **Classification of Crude Drugs** * **Purpose:** * For the systemic and scientific study of crude drugs, it is very essential to classify them in the proper form. A method of classification should be: * Simple * Easy to use * Free from confusion ### **Different ways of classifying the crude drugs are:** 1. **Alphabetical classification:** * Crude drugs are arranged in alphabetical order of their Latin and English names. * This method of classification is adopted by several books and Pharmacopoeias. * Indian Pharmacopoeia * British Pharmacopoeia * British Herbal Pharmacopoeia * United States Pharmacopoeia and National Formulary * British Pharmaceutical Codex * European Pharmacopoeia * **Merits:** * It is easy and quick to use. * There is no repetition of entries and is devoid of confusion. * In this system, location, tracing, and the addition of drug entries is easy. * **Demerits:** * It does not help in distinguishing the source of the drug whether is from plant, animal, or mineral origin. 2. **Taxonomical classification:** * This system is purely botanical classification and it is based on phylogenetic similarities in plants. * Crude drugs are arranged in groups according to their division, class, family, genus, and species. * **Merits:** * Taxonomical classification is helpful for studying evolutionary developments. * **Demerits:** * This system also does not co-relate in between the chemical constituents and biological activity of the drugs. 3. **Morphological classification:** * The drugs are arranged in various groups according to the parts used as drugs like leaf, stem, root, bark, flower, fruit, and seed etc. * In this system of classification, drugs are categorized in two classes: * **Organized drugs:** characterized by the presence of a cellular structure: _Overground organ_: Leaves, Flowers, Fruits, Barks, Seeds, _Underground Organ_: Roots, Rhizomes, Bulbs, Corms. * **Unorganized drugs:** do not represent any cellular structure: Juices, Latex, Resins, Fixed oil, waxes, Gums & mucilage. * **Merits:** * Morphological classification is more helpful to identify and detect adulteration. * This system of classification is more convenient for practical study, especially when the chemical nature of the drug is not clearly understood. * **Demerits:** * The main drawback of morphological classification is that there is no co-relation of chemical constituents with the therapeutic actions. 4. **Pharmacological classification:** * In this classification, crude drugs are arranged according to their pharmacological action or therapeutic use. * This classification is more relevant and is mostly followed method. So the drugs having similar action are kept together. * **Example:** Drugs like digitalis, squill, and strophanthus having cardiotonic action are grouped together. * **Table: Classification of drugs based pharmacological action** * **Pharmacological Action:** Anticancer, Anti-inflammatory, Antiamoebic, Antiasthmatic, Anthelminthic, Antispasmodic, Astringent, Analgesic, Bitter tonic, Carminatives, Purgatives, Expectorant, Cardiotonic, Tranquilizers * **Drugs:** Vinca, Podophyllum, Taxus, Colchicum, Turmeric, Ipecac root, Kurchi bark, Ephedra, Lobelia, Male fern, Quassia wood, Datura, Hyoscyamus, Catechu, Opium, Poppy, Quassia wood, Nux-vomica, Gentian, Coriander, fennel, clove, peppermint, Senna, Rhubarb, Tulsi, Balsam of Tolu, Vasaka, Digitalis, Squill, Strophanthus, Rauwolfia Roots * **Merits:** * This system of classification can be used for suggesting substitutes of drugs if they are not available at a particular place or point of time. * **Demerits:** * Drugs having different action on the body gets classified separately in more than one group that causes ambiguity and confusion. * For example, Cinchona is anti-malarial drug because of the presence of quinine but its effect can be put under the group of drugs affecting heart because of anti-arrhythmic action of quinidine. 5. **Chemical classification:** * In this system of classification, the crude drugs are classified into different groups according to the chemical nature of their most important constituent. * The chemical classification of drugs is dependent upon the grouping of drugs with identical constituents * **Carbohydrates:** * Carbohydrates are polyhydroxy aldehydes or ketones containing an unbroken chain of carbon atoms. * Examples: Gums- Acacia, Tragacanth, Guargum, Mucilages- Plantago seed, Others: Starch, Honey, Agar, Pectin, Cotton * **Glycosides:** * Glycosides are compounds which upon hydrolysis give rise to one or more sugars (glycone) and the non-sugar (aglycone). * Examples: * **Anthraquinone Glycosides:** Aloe, Cascara, Rhubarb, Senna. * **Cardiac Glycosides:** Digitalis, Strophantus, Squill. * **Saponins Glycosides:** Quillaia, Arjuna, Glycyrrhiza * **Tannins:** * Tannins are complex organic, non-nitrogenous derivatives of polyhydroxy benzoic acids. * Examples: Pale catechu, Black catechu, Ashoka bark, Galls, Myrobalan, Bahera, Amla. * **Alkaloids:** * Nitrogenous substance of plant origin * Examples: * **Tropane:** Coca, Belladonna, Datura, Stramonium, Hyoscyamus * **Quinoline:** Cinchona * **Isoquinoline:** Opium, Ipecac, Calumba * **Indole:** Ergot, Rauwolfia * **Amines:** Ephedra * **Purine:** Tea, coffee * **Merits:** * It is a popular approach for phyto-chemical studies. * **Demerits:** * It is very difficult to place the drug containing two different types of chemical constituents. * **Example:** Cinchona contains both alkaloids and glycosides. 6. **Chemotaxonomical classification:** * This system of classification relies on the chemical similarity of a taxon i.e. it is based on the existence of relationship between constituents in various plants. * There are certain types of chemical constituents that characterize certain classes of plants. This gives birth to entirely new concept of chemotaxonomy that utilizes chemical facts/characters for understanding the taxonomical status, relationships, and the evolution of the plants. * **For example,** tropane alkaloids generally occur among the members of Solanaceae thereby, serving as a chemotaxonomic marker. ## **Cultivation** * **Cultivation** of crude drugs can be done from wild or cultivated sources. * **Wild Source:** * **Opium:** only official growers may legally produce herbs. * **Disadvantages of wild drugs:** * **Potentially difficult to transport herbs to the area of processing.** * **Difficult access (e.g., Forests, Mountains etc.).** * **Collector ignorance → admixture of other plants, collection of undesired plant parts or stage of development, or during an incorrect season → loss of medicinal activity.** * **Damage to natural environment → Extinction of a species.** * **Advantages of Cultivated Herbs:** * **Only desired species are collected → uniform quality.** * **Collection, transport & access to processing facilities is improved.** * **Better control of soil quality, pests & plant disease.** * **Supply: Constant & Regular (Controlled).** * **Herb collectors - trained.** ## **Factors affecting cultivation of drugs** * **Altitude:** * Altitude is a very important factor in the cultivation of medicinal plants. * **Tea, cinchona, and eucalyptus** are cultivated favorably at an altitude of 1000-2000 meters. * **Cinnamon and cardamom** are grown at a height of 500-1000 meters, while **senna** can be cultivated at sea level. * **Examples:** _Tea_: 1000-1500 meters, _Cinchona_: 1000-2000 meters, _Cinnamon_: 250-1000 meters, _Clove_: upto 900 meters, _Saffron_: upto 1,250 meters, _Cardamom_: 600-1,600 meters * **Temperature:** * Excessive temperature, as well as frost, also affect the quality of medicinal plants adversely. * **Examples:** * Camphor and coffee cannot withstand frost, whereas saffron needs only cold climate and pyrethrum requires dry weather for cultivation. * **Rainfall:** * Except for the xerophytic plants like aloe, acacia and few others. * Most of the plants need either proper arrangements for irrigation or sufficient rainfall for their favorable development. * **Soil and soil fertility:** * Soil is the most important natural resource as it supports the growth of all plants. * Soil provides mechanical anchorage, as well as water and essential plant food elements for plant growth. * **Soil is made up of five components:** * Mineral matter. * Organic matter. * Soil air. * Soil water. * Soil organism. * **Soil containing less than 0.5% of organic matter is described as poor. If more than 1.5 to 5% of organic matter is present, it is described as rich soil.** * **The pH of soil decides favorable growth of plants and the presence of microorganisms.** The maximum availability of plant nutrients is in between the pH range of 6.5 to 7.5. * **Groundnut, sunflower seeds, cotton, and rice** grow better in alkaline soils only. * **Tobacco, cinchona, tea, and potato** grow well only in acidic soils. * **Fertilizers:** * Fertilizers are nutrients which are necessary for the development & growth of the plant. Every element has to perform a specific function in the growth and development of plants. * For the vegetative growth, plants need carbon dioxide, sunlight, water, and mineral matter. Plants are also in need of 16 nutrient elements for synthesizing various compounds. * **Primary nutrients:** Nitrogen, phosphorus and potassium. * **Secondary nutrients:** Magnesium, calcium and sulfur are required in small quantities. * **Trace elements:** Copper, manganese, iron, boron, molybdenum, and zinc. _Carbon, oxygen, hydrogen, and chlorine are provided to plants from water and air._ ## **Plant growth regulators (Plant hormones)** * Plant growth regulators are the organic compounds that affect the morphological structure or physiological processes of plants in low concentrations. * **Natural:** found naturally in plants * **Synthetic:** human-made Both groups regulate or influence: * Cell division * Cell differentiation * Root and shoot growth * Senescence (plant aging) * **Major classes of plant growth regulators (Plant hormones):** * 1. **Auxins:** promote elongation of coleoptile tissues. Examples: Internodes elongation, leaf growth, fruit growth, apical dominance. * *Natural:* Indole acetic acid (IAA) * *Synthetic:* Indole butyric acid (IBA), a-napthyl acetic acid (NAA) * 2. **Gibberellins (GA):** natural plant growth regulator - stimulates stem growth through cell division and cell elongation. Commercial supplies obtained from the fungus Gibberella fujikuroi. Gibberellins are used currently for promoting vegetative and fruit growth, flower initiation and induction of parthenocarpy. * 3. **Cytokinins:** * *Natural:* Zeatin * *Synthetic:* Kinetin * Promote cell division and delay leaf aging. * Used as growth promoter in tissue culture techniques. * Slow the process of senescence (Plant aging) by preventing the breakdown of chlorophyll in the leaf. * 4. **Ethylene:** * Present in the form of volatile gas. * Present in ripening fruits, flowers, stems, roots, tubers, and seeds. * 5. **Abscisic Acid (ABA):** * Natural plant growth inhibitor - Present in different organs such as leaves, stems, flowers, and fruits. ## **Collection of medicinal plants** * Drugs may be collected from wild or cultivated plants. * It is known that the active constituents of medicinal plants are affected by many factors and may vary during the course of plant growth. Proper time of collection is very important to obtain a drug of a good quality. * **Factors affecting collection:** * **1. Time of the year:** * The plant may contain a substance in winter that is not present in summer, or its amount varies markedly. * For example, _Rhubarb contains no anthraquinone in winter, instead it contains anthranols, which in summer, are oxidized to anthraquinones._ * Another example: _Colchicum corm is free from bitterness and is devoid of the alkaloid colchicine in autumn, hence is used in Austria as a food, instead of potatoes. Bitterness starts to appear in spring and early summer when it is used as a drug._ * **2. Time of the day:** * Some drugs, like **Digitalis**, contain different amounts of active constituents in different times of the day. Being highest in the afternoon. * **3. Stage of maturity and age:** * The value and content of active constituents of many drugs depends on the stage of maturity and age. * **Conium fruits:** contain coniin when fruits are mature and unripe. * **Santonica flowers:** are rich in santonin, when unexpanded, when it starts to open, the santonin content decreases. * **Rules for collection:** * The following general rules are based on assuming that the material is best collected, when the organ in question has reached its optimal state of development. * **1. Roots and rhizomes:** are collected at the end of the vegetation period, i.e. usually in the autumn. In most cases, they must be washed free of adhering soil and sand. * **2. Bark:** is collected in the spring. * **3. Leaves and herbs:** are collected at the flowering stage. * **4. Flowers:** are usually gathered when fully developed. * **5. Fruits and seeds:** are collected when fully ripe. * **Methods of collection:** * Medicinal plants must be largely collected by hand. This is especially true in the case of wild plants. * With cultivation on a large scale, it may be possible to use modern agricultural harvesters. ## **Drying of crude drugs:** * The most common method for preserving plant material is drying. * **Living plant material has a high water content:** leaves may contain 60-90% water, roots, and rhizomes 70-85%, and wood 40-50%. The lowest percentage, often no more than 5-10%, is found in seeds. * **Reasons for drying:** * 1. To help in their preservation. * 2. To fix their constituents, by preventing reactions that may occur in the presence of water. * 3. To prevent the growth of microorganisms such as bacteria and fungi. * 4. To facilitate their grinding. * 5. To reduce their size and weight. * 6. Insufficient drying favors spoilage by microorganisms and makes it possible for enzymatic destruction. * **Methods of drying:** * **1. Natural drying:** is accomplished by natural air in sun or shade. * **2. Artificial drying:** * This is a rapid method done at well-controlled temperature. * It is accomplished by: * Direct fire * Use of heated stones. * Use of stoves. * **3. Lyophilization (freeze drying):** * Frozen material is placed in an evacuated apparatus which has a cold surface maintained at -60 to -80 °C. Water vapor from the frozen material passes rapidly to the cold surface. * It is used for drying heat-sensitive substances e.g. antibiotics and proteins. * **4. Chemical drying using desiccators:** * An absolutely dried drug is that completely freed from water, when exposed to air it absorbs 8-10% of moisture and is called _air-dry drug._ ## **Storage of crude drugs:** * It is essential to store them in a dry condition in carefully closed containers. * Storage represents the last stage of preparing crude drugs. Drugs usually deteriorate along the time of storage. * Improper methods of storing and inadequate protection during storage can cause a pronounced deterioration. * **There are two principal reasons for deterioration:** * **Physiochemical:** Moisture, Heat, Air, Light. * **Biological:** Fungi, Bacteria, Insects and rodents. ## **Pharmacognostic Evaluation of Medicinal Plants:** * **Preparation of crude drugs:** * Extracts can be defined as preparations of crude drugs which contain all the constituents which are soluble in the solvent used in making the extract. * Tinctures are prepared by extraction of the crude drug with five to ten parts of ethanol of varying concentration, without concentration of the final product. * **Choice of solvent:** * The ideal solvent for a certain pharmacologically active constituent should: * Be highly selective for the compound to be extracted. * Not react with the extracted compound or with other compounds in the plant material. * Have a low price. * Be harmless to man and to the environment. * Be completely volatile. * **According to the pharmacopoeias, _ethyl alcohol_ is the solvent of choice for obtaining classic extracts such as tinctures.** * **The ethanol is usually mixed with water:** * 1. To induce swelling of the plant particles. * 2. To increase the porosity of the cell walls which facilitates the diffusion of extracted substances from inside the cells to the surrounding solvent. * **For extraction of barks, roots, woody parts and seeds, the ideal alcohol/water ratio is about 7:3 or 8:2.** * **For leaves or aerial green parts, the ratio 1:1 is usually preferred in order to avoid extraction of chlorophyll.** * **Methods of Extraction:** * 1. Infusion * 2. Maceration * 3. Percolation * 4. Digestion * 5. Decoction * 6. Continuous hot extraction * 7. Solvent-solvent precipitation * 8. Liquid-liquid extraction * 9. Distillation * 10. Specific procedures. ## **Cell Content ** * All cells are living organisms as they require energy to survive. This energy is derived from various metabolic processes within the cell. Metabolism requires nutrients (which need to be taken up by the cell) and various enzymes (catalysts) that actually digest the nutrients. The enzymes are produced within the cell itself from cell organelles, and the waste products after the digestion are then removed by the cell membrane. * **Living protoplasts:** Nucleus, cytoplasm, vacuoles, plastids, mitochondria. * **Non-protoplasmic components:** Classified as 'ergastic' substances: Starch, Crystals, Alkaloids, Oil, Protein, Tannins. * **Not diagnostically useful:** Living protoplasts * **Very useful for identification:** Non-protoplasmic components ## **Volatile oils:** * They are odorous principles found in plants and evaporate, when exposed to air at ordinary temperature. * They pre-exist in plants in particular secretory parts such as: * Glandular hairs. * Parenchyma cells. * Vittae or oil tubes. * Epidermal tissues of lemon and orange. * In lysigenous or schizogenous passages. * The main component of volatile oil are derivatives of terpenes (C5H8). * They have high refractive indices and generally are optically active. * They are immiscible with water and freely soluble in organic solvent such as alcohol, ether, chloroform, acetone etc. * Mostly volatile oils are liquid except menthol, thymol, anethol which are solids at 15.5 °C. ## **Tannins:** * **Tannins are complex organic, non-nitrogenous derivatives of poly hydroxyl benzoic acids.** * The word tannins is derived from _tan_ which means conversion of hides and skins to _leather_ by forming insoluble compounds with proteins. * **They are present in aerial parts, e.g., leaves, fruits, barks, and stems; generally occur in immature fruits but disappear during the ripening process.** * **Types of Tannins:** * **True tannins:** High molecular compounds, shows positive test of Goldbeaters skin test. * **Pseudo tannins:** Low molecular compounds, shows negative reaction with Goldbeaters skin test. ## **Chemical test of Tannins:** * **Goldbeaters skin test:** Small piece of skin (membrane prepared from intestine of an ox) + soaked in 2% HCl + washed with water + placed in solution of tannins for 5 mints. Skin piece again washed with water and kept in solution FeSO4 → A brown or black color is produced on the skin due to the presence of tannins. * **Vanillin test:** Drug solution + Vanillin hydrochloride → Pink or red colour formed. * **Matchstick test:** A matchstick is dipped in drug solution + dried near the burner + moistened with conc. HCl + then warming near the burner → Pink or red color formed. ## **Alkaloids:** * **Defination**: (Alkali-like) they are basic in nature. Derived from amino acid present in plant sources. Contain one or more nitrogen atoms (usually in a heterocyclic ring). Marked physiological action on man or other animals. * **Deviation from Definition:** * **Basicity:** Some alkaloids are not basic, like Colchicine and Piperine. * **Nitrogen:** The nitrogen in some alkaloids is not in a heterocyclic ring, like Ephedrine. * **Types of Alkaloids:** * **True Alkaloids:** Nitrogen is part of a heterocyclic ring. * **Derived from Amino acid:** _e.g., Quinine_: R = OCH3. * **Proto Alkaloids:** Does not have heterocyclic ring with nitrogen. * **Derived from Amino acid:** e.g., _Colchicine_: R = COCH3. * **Pseudo Alkaloids:** Nitrogen is part of a heterocyclic ring. * **Not derived from Amino acid:** e.g., _caffeine_ ## **Occurrence and Distribution** * **PLANTS:** * Rare in lower plants. * In higher plants - about 10 to 25%. * Dicots are more rich in alkaloids than Monocots. * Families rich in Alkaloids: Apocynaceae, Loganiaceae, Liliaceae, Rubiaceae, Solanaceae and Papaveraceae. * Families free from Alkaloids: Rosaceae, Labiatae. * **ANIMALS:** * **Ergot alkaloids:** Ergotamine and erogmetrine from Ergot fungus. * **Muscopyridine:** from Musk deer and **Lycopodine:** from Lycopodium spores. ## **Distribution in Plant:** * All Parts: Catharanthus * Barks: Cinchona * Seeds: Nux vomica * Roots: Aconite * Rhizomes: Rauwolfia * Flowering tops: Datura * Fruits: Black pepper * Leaves: Tobacco * Latex: Opium ## **Function in Plants:** * They may act as protective against insects and herbivores due to their bitterness and toxicity. * Source of nitrogen in case of nitrogen deficiency. * They, sometimes, act as growth regulators in certain metabolic systems. * They may be utilized as a source of energy in case of deficiency in carbon dioxide assimilation. ## **Qualitative test for Alkaloids:** * Indicates the presence or absence of alkaloids * **Dragendorff's reagent:** (Potassium bismuth iodide) → Orange coloured ppt. * **Mayer's reagent:** (Potassium mercuric iodide) → Cream coloured ppt. * **Wagner's reagent:** (Iodine in potassium iodide) → Red brown coloured ppt. * **Hagers reagent:** (Picric acid) → Yellow ppt.