Comprehensive Study Guide to Drug Classification Systems

Prerequisites for Drug Classification

To investigate individual drugs systematically, one must follow a drug classification scheme. A classification technique should meet the following criteria:

  • Simple: It should be straightforward to implement.
  • Easy to Use: It should facilitate quick reference.
  • Unambiguous: It must be devoid of ambiguity and potential for misunderstanding.

While every method has specific advantages and disadvantages due to widespread distribution, drugs are generally categorized into the following seven systems:

  1. Alphabetical
  2. Taxonomical
  3. Morphological
  4. Pharmacological
  5. Chemical
  6. Chemotaxonomical
  7. Serotaxonomical

Alphabetical Classification

This is the most basic method for categorizing disconnected objects. Crude drugs are organized alphabetically based on their Latin names, English names (common names), or regional names (vernacular names).

  • Source References: The following pharmacopoeias and reference books utilize this scheme:
    • Indian Pharmacopoeia
    • British Pharmacopoeia
    • British Herbal Pharmacopoeia
    • United States Pharmacopoeia (USP) and National Formulary
    • European Pharmacopoeia
  • Naming Variations: In the European Pharmacopoeia, drugs are arranged according to their Latin names. In contrast, the USP and the British Pharmaceutical Codex (BPC) arrange them in English.
  • Merits:
    • It is quick and easy to use.
    • It eliminates repetition of entries and prevents confusion.
    • Tracing, locating, and adding new drug entries is simplified in this system.
  • Demerits:
    • There is no inherent relationship between successive drug entries.
  • Examples: Acacia, Benzoin, Cinchona, Dill, Ergot, Fennel, Gentian, Hyoscyamus, Ipecac, Jalap, Kurchi, Liquorice, Mint, Nuxvomica, Opium, Podophyllum, Quassia, Rauwolfia, Senna, Vasaka, Wool fat, yellow bees wax, Zeodary.

Taxonomical Classification

(Relevant for GPAT 20192019, GPAT 20142014)

Crude drugs are classified according to the biological hierarchy: kingdom, subkingdom, division, class, order, family, genus, and species.

  • Hierarchy Definitions:

    • Class:
      • Angiospermae (Angiosperms): Plants that produce flowers.
      • Gymnospermae (Gymnosperms): Plants that do not produce flowers.
    • Subclass:
      • Dicotyledonae (Dicots): Plants with two seed leaves.
      • Monocotyledonae (Monocots): Plants with one seed leaf.
    • Superorder: A group of related plant families categorized by the order in which they developed differences from a common ancestor.
      • Dicotyledonae superorders (six): Magnoliidae, Hamamelidae, Caryophyllidae, Dilleniidae, Rosidae, and Asteridae.
      • Monocotyledonae superorders (four): Alismatidae, Commelinidae, Arecidae, and Liliidae.
      • Naming Convention: Names ends in −idae-idae.
    • Order: Subdivisions of superorders. Names end in −ales-ales.
    • Family: Subdivisions of orders. These represent plants with many shared botanical features; this is the highest standard level of classification usually used.
    • Subfamily: Division of a family based on significant botanical differences. Names end in −oideae-oideae.
    • Tribe: Division within a family based on smaller botanical differences. Names end in −eae-eae.
    • Subtribe: Further division based on even smaller differences recognizable primarily to botanists. Names end in −inae-inae.
    • Genus: The familiar part of the plant name (e.g., Papaver for Poppy or Aquilegia for Columbine).
    • Species: Define the individual plant based on characteristics like leaf shape, flower color, or origin location.
    • Variety (var.): Plants slightly different from the species, but more signifiant than a form.
    • Form (f.): Plants with minor botanical differences, such as flower color or leaf shape.
    • Cultivar (cv.): A cultivated variety produced via hybridization or natural occurrence, reproduced vegetatively or by seed. The name is written in single quotes or preceded by "cv."; it remains in the original language of the person who described it.

  • Taxonomic Example (Linnaeus, 1707−17781707-1778): Peppermint

    • Division: Angiospermae
    • Class: Dicotyledoneae
    • Subclass: Sympetalae
    • Order: Tubiflorae
    • Family: Labiatae (Lamiaceae)
    • Genus: Mentha
    • Species: Mentha piperita Linnaeus (peppermint)
    • Varieties: Mentha piperita var. officinalis (White Peppermint); Mentha piperita var. vulgaris (Black Peppermint)

  • Merits: Useful for studying evolutionary development.

  • Demerits: No correlation between chemical constituents and biological activity.

Morphological Classification

Drugs are arranged based on external/morphological characters of the plant or animal parts used as the drug.

  • Organized Drugs:     These consist of direct parts of the plant or animal and possess a cellular structure. They are identified by morphological characters.

    • Woods: Sandalwood
    • Leaves: Eucalyptus, Tulsi, Tea
    • Barks: Arjuna, Ashoka, Cinnamon
    • Flowering parts: Clove, Saffron
    • Fruits: Amla, Coriander, Fennel
    • Seeds: Black Mustard, Cardamom, Ispaghula
    • Roots & Rhizomes: Ginger, Glycyrrhiza, Turmeric
    • Plants & Herbs: Vinca, Neem, Brahmi
    • Hair & Fibres (GPAT 20232023): Cotton, Jute, Silk

  • Unorganized Drugs:     These are products of plants, animals, or minerals and lack a well-defined cellular structure. They are typically identified by organoleptic properties.

    • Dried latex: Opium, Papain
    • Dried Juice: Aloe, Kino
    • Dried extracts: Agar, Black catechu
    • Waxes: Beeswax, Carnauba wax
    • Gums: Acacia, Tragacanth
    • Resins: Asafoetida, Benzoin
    • Volatile oil: Sandalwood, Clove, Eucalyptus
    • Fixed oils and Fats: Castor, Coconut, Olive, Kokum butter
    • Animal Products: Beeswax, Gelatin, Honey
    • Fossil organism & Minerals: Bentonite, Kaolin, Talc

  • Merits:

    • Helpful for identifying drugs and detecting adulteration.
    • Convenient for practical study when the chemical nature is not understood.

  • Demerits:

    • No correlation between chemical constituents and therapeutic action.
    • Repetition of plants occurs across different categories.

Pharmacological Classification

Grouping occurs based on the pharmacological action or therapeutic use of the most important constituent.

  • Detailed Action and Example Mapping:

    • G.I.T. (Gastrointestinal Tract) Drugs:
      • Bitters: Cinchona, Quassia, Gentian
      • Cathartic: Senna
      • Purgative: Senna, Castor Oil
      • Laxative: Agar, Isabgol, Banana
      • Antiamoebic: Kurchi, Ipecac
      • Emetic: Ipecac
      • Carminative: Fennel, Cardamom, Mentha
    • Respiratory Tract Drugs:
      • Expectorant: Vasaka, Liquorice, Ipecac
      • Antitussive: Opium (codeine)
      • Bronchodilators: Ephedra, Tea
    • Autonomic Nervous System (ANS) Drugs:
      • Cholinergic: Physostigma, Pilocarpus
      • Anticholinergic: Datura, Belladonna
      • Adrenergic: Ephedra
    • Cardiovascular System (CVS) Drugs:
      • Cardiotonic: Digitalis, Strophanthus, Squill
      • Cardiac Depressant: Cinchona, Veratrum
      • Antihypertensive: Rauwolfia
      • Vasoconstrictor: Ergot
    • Central Nervous System (CNS) Drugs:
      • Central Analgesic: Opium (morphine)
      • CNS Stimulant: Tea, Coffee
      • CNS Depressant: Opium, Belladonna, Hyoscyamus
      • Analeptic: Nuxvomica, Camphor, Lobelia
    • Other Specialized Actions:
      • Antispasmodic: Datura, Hyoscyamus, Opium, Curare
      • Antimalarial: Cinchona, Artemisia
      • Astringent: Catechu, Myrobalans
      • Anthelmintic: Quassia, Vidang
      • Antirheumatic: Guggul, Colchicum
      • Anticancer: Vinca, Podophyllum, Taxus
      • Local Anaesthetic: Coca
      • Immunomodulatory: Ginseng, Ashwagandha, Tulsi
      • Immunizing Agent: Vaccines, Sera, Anti-toxin
      • Skin membrane: Beeswax, Wool fat, Balsam of Tolu, Balsam of Peru
      • Chemotherapeutic: Antibiotics

  • Merits: Helps suggest substitutes when a specific drug is unavailable.

  • Demerits: Causes ambiguity because drugs with multiple actions (e.g., Cinchona) are classified in multiple groups.

Chemical Classification

Drugs are divided according to the chemical nature of their primary constituent.

  • Carbohydrates (Polyhydroxy aldehydes/ketones):

    • Gums: Acacia, Tragacanth
    • Mucilages: Plantago seed
    • Others: Starch, Honey, Agar, Cotton

  • Glycosides (Sugar + Non-sugar components):

    • Anthraquinone: Aloe, Senna
    • Saponins: Arjuna, Glycyrrhiza
    • Cyanophore: Wild cherry bark
    • Isothiocyanate: Mustard
    • Cardiac: Digitalis, Strophanthus
    • Bitter: Gentian, Kalmegh

  • Tannins (Non-nitrogenous polyhydroxy benzoic acid derivatives): Catechu, Ashoka, Arjuna, Harad, Bahera, Amla

  • Volatile Oils (Terpenes/Oxygenated products): Cinnamon, Fennel, Dill, Caraway, Coriander, Cardamom, Orange peel, Mint, Clove

  • Lipids:

    • Fixed Oils: Castor, Olive, Almond, Shark liver oil
    • Fats: Theobroma, Lanolin
    • Waxes: Beeswax, Spermaceti

  • Resins (Complex mixtures): Podophyllum, Cannabis, Capsicum, Turmeric, Balsam of Tolu and Peru, Asafoetida, Ginger

  • Alkaloids (Nitrogenous plant substances):

    • Pyridine and Piperidine: Lobelia, Nicotiana
    • Tropane: Coca, Belladonna, Datura
    • Quinoline: Cinchona
    • Isoquinoline: Opium, Ipecac
    • Indole: Ergot, Rauwolfia
    • Amines: Ephedra
    • Purine: Tea, Coffee

  • Merits: Popular for phytochemical studies.

  • Demerits: Ambiguity occurs when a drug contains compounds from multiple chemical groups.

Chemotaxonomical Classification

(Relevant for GPAT 20212021)

This system relies on the chemical similarity within a taxon, based on the relationships between constituents in various plants. Chemical characters are used to understand taxonomical status and evolution.

  • Examples of Chemotaxonomic Markers:
    • Tropane alkaloids in Solanaceae members.
    • Berberine alkaloids in Berberis and Argemone.
    • Rutin in Rutaceae members.
    • Ranunculaceous alkaloids in members of the Ranunculaceae family.
    • Sulphur containing compounds in Allium cepa, Allium sativum, and Allium ascalonicum.
    • Cardiac Glycosides in Digitalis purpurea and Digitalis lanata.
    • Anthraquinone Glycosides in Aloe barbadensis and Aloe ferox.

Serotaxonomical Classification

This involves the application of serology (the study of antigen−antibodyantigen-antibody reactions) to solve taxonomical problems. Proteins serve as the carriers of taxonomical information and are used as antigens.

  • Key Definitions:
    • Antigens: Substances that stimulate the formation of antibodies.
    • Antibodies: Specific protein molecules produced by plasma cells in the immune system.
  • Process Steps:
    1. Extract the plant protein (antigen).
    2. Inject the antigen into the bloodstream of an experimental animal.
    3. The animal produces a specific antibody response.
    4. Collect the serum containing the antibodies (antiserum).
    5. React the antiserum in vitro with the original antigenic protein and proteins from other taxa.
    6. Observe the amount of precipitation; the degree of precipitation indicates the degree of homology between the taxa.