Classification of Crude Drugs: The most important natural sources of drugs are higher plants, microbes and animals and marine organisms. Some useful products are obtained from minerals that are both organic and inorganic. To pursue (or to follow) the study of the individual drugs, one must adopt some particular sequence of arrangement, and this is referred to as a system of classification of drugs. A method of classification should be:
- easy to use, and
- free from confusion and ambiguities.
Because of their wide distribution, each arrangement of classification has its own merits and demerits, but for study, the drugs are classified in the following different ways:
- Alphabetical classification
- Taxonomical classification
- Morphological classification
- Pharmacological classification
- Chemical classification
- Chemotaxonomical classification
- Serotaxonomical classification
Alphabetical classification is the simplest way of classification of any disconnected items. Crude drugs are arranged in alphabetical order of their Latin and English names (common names) or sometimes local language names (vernacular names). Some of the pharmacopoeias, dictionaries and reference books that classify crude drugs according to this system are as follows:
- Indian Pharmacopoeia
- British Pharmacopoeia
- British Herbal Pharmacopoeia
- United States Pharmacopoeia and National Formulary
- British Pharmaceutical Codex
- European Pharmacopoeia
In European Pharmacopoeia these are arranged according to their names in Latin whereas, in the United States Pharmacopoeia (U.S.P.) and British Pharmaceutical Codex (B.P.C.), are arranged in English.
- It is easy and quick to use.
- There is no repetition of entries and is devoid of confusion.
- In this system location, tracing and addition of drug entries are easy.
There is no relationship between previous and successive drug entries.
Examples: Acacia, Benzoin, Cinchona, Dill, Ergot, Fennel, Gentian, Hyoscyamus, Ipecacuanha, Jalap, Kurchi, Liquorice, Mints, Nux vomica, Opium, Podophyllum, Quassia, Rauwolfia, Senna, Vasaka, Wool fat, Yellow beeswax, Zeodary.
All the plants possess different characteristics of morphological, microscopical, chemical, embryological, serological and genetics. In this classification, the crude drugs are classified according to kingdom, subkingdom, division, class, order, family, genus and species as follows.
Class: Angiospermae (Angiosperms) are plants that produce flowers and Gymnospermae (Gymnosperms) which don’t produce flowers.
Subclass: Dicotyledonae (Dicotyledons, Dicots) are plants with two seed leaves; Monocotyledonae (Monocotyledons, Monocots) with one seed leaf.
Superorder: A group of related plant families, classified in the order in which they are thought to have developed their differences from a common ancestor. There are six superorders in the Dicotyledonae (Magnoliidae, Hamamelidae, Caryophyllidae, Dilleniidae, Rosidae, Asteridae), and four superorders in the Monocotyledonae (Alismatidae, Commelinidae, Arecidae, and Liliidae). The names of the superorders end in –idae.
Order: Each superorder is further divided into several orders. The names of the end of the order in –ales.
Family: Each order is divided into families. These are plants with many botanical features in common and are the highest classification normally used. At this level, the similarity between plants is often easily recognizable by the layman. Modern botanical classification assigns a type of plant to each family, which has the particular characteristics that separate this group of plants from others, and names the family after this plant.
The number of plant families varies according to the botanist whose classification you follow. Some botanists recognize only 150 or so families, preferring to classify other similar plants as subfamilies, while others recognize nearly 500 plant families. A widely accepted system is that devised by Cronquist in 1968, which is only slightly revised today. The names of the families end in –aceae.
Subfamily: The family may be further divided into several subfamilies, which group together plants within the family that have some significant botanical differences. The names of the subfamilies end in –oideae.
Tribe: A further division of plants within a family, based on smaller botanical differences, bin still usually comprising many different plants. The names of the tribes end in –eae.
Subtribe: A further division based on even smaller botanical differences, often only recognizable to botanists. The names of the subtribes end in –inae.
Genus: This is the part of the plant name that is most familiar; the normal name that you give a plant—Papaver (Poppy), Aquilegia (Columbine), and so on. The plants in a genus are often easily recognizable as belonging to the same group.
Species: This is the level that defines an individual plant. Often, the name will describe some aspect of the plant— the colour of the flowers, size or shape of the leaves, or it may be named after the place where it was found. Together, the genus and species name refer to only one plant, and they are used to identify that particular plant. Sometimes, the species is further divided into subspecies that contain plants not quite so distinct that they are classified as varieties. The name, of the species, should be written after the genus name, in small letters, with no capital letter.
Variety: A variety is a plant that is only slightly different from the species plant, but the differences are not so insignificant as the differences in a form. The Latin is varieties, which is usually abbreviated to var. The name follows the genus and species name, with var. before the individual variety name.
Form: A form is a plant within a species that has minor botanical differences, such as the colour of the flower or the shape of the leaves. The name follows the genus and species name, with form (or f.) before the individual variety name.
Cultivar: A cultivar is a cultivated variety—a particular plant that has arisen either naturally or through deliberate hybridization, and can be reproduced (vegetatively or by seed) to produce more of the same plant.
The name follows the genus and species name. It is written in the language of the person who described it, and should not be translated. It is either written in single quotation marks or has a cv. written in front of the name.
Taxonomical classification helps study evolutionary developments.
This system also does not correlate between the chemical constituents and biological activity of the drugs.
In this system, the drugs are arranged according to the morphological or external characters of the plant parts or animal parts, i.e. which part of the plant is used as a drug, e.g. leaves, roots, stem, etc. The drugs obtained from the direct parts of the plants and containing cellular tissues are called organized drugs, e.g. rhizomes, barks, leaves, fruits, entire plants, hairs and fibres. The drugs which are prepared from plants by some intermediate physical processes such as incision, drying or extraction with a solvent and not containing any cellular plant tissues are called unorganized drugs. Aloe juice, opium latex, agar, gambir, gelatin, tragacanth, benzoin, honey, beeswax, lemongrass oil, etc., are examples of unorganized drugs.
- Woods: Quassia, Sandalwood and Red Sandalwood.
- Leaves: Digitalis, Eucalyptus, Gymnema, Mint, Senna, Spearmint, Squill, Tulsi, Vasaka, Coca, Buchu, Hamamelis, Hyoscyamus, Belladonna, Tea.
- Barks: Arjuna, Ashoka, Cascara, Cassia, Cinchona, Cinnamon, Kurchi, Quillia, Wild cherry.
- Flowering parts: Clove, Pyrethrum, Saffron, Santonica, Chamomile.
- Fruits: Amla, Anise, Bael, Bahera, Bitter Orange peel, Capsicum, Caraway, Cardamom, Colocynth, Coriander, Cumin, Dill, Fennel, Gokhru, Hirda, Lemon peel, Senna pod, Star anise, Tamarind, Vidang.
- Seeds: Bitter almond, Black Mustard, Cardamom, Colchicum, Ispaghula, Kaladana, Linseed, Nutmeg, Nux vomica, Physostigma, Psyllium, Strophanthus, White mustard.
- Roots and Rhizomes: Aconite, Ashwagandha, Calamus, Calumba, Colchicum corm, Dioscorea, Galanga, Garlic, Gention, Ginger, Ginseng, Glycyrrhiza, Podophyllum, Ipecac, Ipomoea, Jalap, Jatamansi, Rauwolfia, Rhubarb, Sassurea, Senega, Shatavari, Turmeric, Valerian, Squill.
- Plants and Herbs: Ergot, Ephedra, Bacopa, Andrographis, Kalmegh, Yeast, Vinca, Datura, Centella.
- Hair and Fibres: Cotton, Hemp, Jute, Silk, Flax.
- Dried latex: Opium, Papain
- Dried Juice: Aloe, Kino
- Dried extracts: Agar, Alginate, Black catechu, Pale catechu, Pectin
- Waxes: Beeswax, Spermaceti, Carnauba wax
- Gums: Acacia, Guar Gum, Indian Gum, Sterculia, Tragacenth
- Resins: Asafoetida, Benzoin, Colophony, copaiba Guaiacum, Guggul, Mastic, Coal tar, Tar, Tolu balsam, Storax, Sandarac.
- Volatile oil: Turpentine, Anise, Coriander, Peppermint, Rosemary, Sandalwood, Cinnamon, Lemon, Caraway, Dill, Clove, Eucalyptus, Nutmeg, Camphor.
- Fixed oils and Fats: Arachis, Castor, Chalmoogra, Coconut, Cottonseed, Linseed, Olive, Sesame, Almond, Theobroma, Cod-liver, Halibut liver, Kokum butter.
- Animal Products: Beeswax, Cantharides, Cod-liver oil, Gelatin, Halibut liver oil, Honey, Shark liver oil, shellac, Spermaceti wax, wool fat, musk, Lactose.
- Fossil organism and Minerals: Bentonite, Kaolin, Kiesslguhr, Talc.
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.
- The main drawback of morphological classification is that there is no correlation of chemical constituents with the therapeutic actions.
- Repetition of drugs or plants occurs.
Grouping of drugs according to their pharmacological action or of most important constituent or their therapeutic use is termed as pharmacological or therapeutic classification of drug. This classification is more relevant and is mostly a followed method. Drugs like digitalis, squill and strophanthus having cardiotonic action are grouped irrespective of their parts used or phylogenetic relationship or the nature of phytoconstituents they contain.
This system of classification can be used for suggesting substitutes for drugs if they are not available at a particular place or point in time.
Drugs having different actions on the body get classified separately in more than one group causes ambiguity and confusion. Cinchona is an antimalarial drug because of the presence of quinine but can be put under the group of the drug affecting the heart because of the antiarrhythmic action of quinidine.
Depending upon the active constituents, the crude drugs are classified. The plants contain various constituents in them like alkaloids, glycosides, tannins, carbohydrates, saponins, etc. Irrespective of the morphological or taxonomical characters, the drugs with similar chemical constituents are grouped into the same group. The examples are shown in this table.
It is a popular approach for phytochemical studies.
Ambiguities arise when particular drugs possess several compounds belonging to different groups of compounds.
This system of classification relies on the chemical similarity of a taxon, i.e. it is based on the existence of a relationship between constituents in various plants. Certain types of chemical constituents characterize certain classes of plants. This gives birth to entirely a 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. Similarly, other secondary plant metabolites can serve as the basis of the classification of crude drugs. The berberine alkaloid in Berberis and Argemone, Rutin in Rutaceae members, Ranunculaceae alkaloids among its members, etc., are other examples.
It is the latest system of classification that gives more scope for understanding the relationship between chemical constituents, their biosynthesis and their possible action.
The serotaxonomy can be explained as the study of the application or the utility of serology in solving taxonomical problems. Serology can be defined as the study of the antigen-antibody reaction. Antigens are those substances that can stimulate the formation of the antibody. Antibodies are highly specific protein molecules produced by plasma cells in the immune system. Protein is the carrier of the taxonomical information and is commonly used as an antigen in serotaxonomy.
It expresses the similarities and the dissimilarities among different taxa, and these data are helpful in taxonomy. It determines the degree of similarity between species, genera, family, etc., by comparing the reaction with antigens from various plant taxa with antibodies present against a given taxon.
Serology helps in comparing nonmorphological characteristics, which helps in the taxonomical data. This technique also helps in the comparison of single proteins from different plant taxa.
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