Pharmacognosy - 2. Classification of Crude Drugs
Classification of Crude Drugs
By Mr. Bhosale, SKCP, Kasbe Digraj
Introduction
The most important natural sources of drugs are higher plant, microbes and animals and marine organisms. Some useful products are obtained from minerals that are both organic and inorganic in nature. Crude drugs obtained from different natural sources are used in treatment of a wide spectrum of diseases. For their adequate study, it is necessary to arrange them in scientific and systematic manner. Their huge number and varied occurrence make it difficult to put them in a uniform pattern. In order to pursue (or to follow) the study of the individual drugs, one must adopt some particular sequence of arrangement, and this is referred to a system of classification of drugs.
A method of classification should be:
- a) simple,
- b) easy to use, and
- c) free from confusion and ambiguities.
Because of their wide distribution, each arrangement of classification has its own merits and demerits, but for the purpose of study the crude drugs are classified in the following different ways:
- Alphabetical classification
- Morphological classification
- Pharmacological classification
- Taxonomical classification
- Chemical classification
- Chemo-taxonomical classification
1. Alphabetical Classification
Crude drugs are classified based on the starting letter of their alphabet. Either Latin or vernacular names may be used. This arrangement is employed for dictionaries, pharmacopoeias, etc. It is suitable for quick reference, it gives no indication of inter relationships between drugs.
Alphabetical classification is found in following:
- Indian Pharmacopoeia.
- British Pharmacopoeia.
- British Herbal Compendium.
- British Herbal Medicine.
- British Herbal Pharmacopoeia
- Indian Herbal Pharmacopoeia
- British Pharmaceutical Codex (BPC)
- National Formulary (NF)
- United State of Pharmacopoeia (USP)
- European Pharmacopoeia.
- Extra Pharmacopoeia.
Advantages:
- Easy to find drugs because they are arrange alphabetically.
- No repetition of entries which avoids confusion.
- Location, tracing and addition of drug is easy.
Disadvantages:
- Unable to distinguish from plants, animal and mineral sources.
- These type of classification is unable to indicate the whether drug is organised or unorganised.
- Unable to indicate interrelationship between drug.
2. Morphological Classification
Morphological classification of crude drugs is a system that arranges crude drugs based on the external characteristics of the plant or animal parts used to make them.
In this method of classification, all the crude drugs are classified into two categories viz:-
- Organized crude drugs (Cellular).
- Unorganized crude drugs (Acellular).
① Organized crude drugs (Cellular)
These crude drugs are made up of cells and have a definite cellular structure. They are the direct parts of the plants or animals. They are also known as cellular crude drugs.
Examples:
- Leaves - Senna, Digitalis, Tobacco.
- Barks - Ashoka, Cinnamon, Cinchona, Cascara.
- Fruits - Coriander, Cardamom, Dill, Fennel.
- Seeds - Isapgol, Linseed, Nuxvomica.
- Roots & Rhizomes - Aconite, Ginger, Rauwolfia, Rhubarb, Turmeric.
- Flowers - Pyrethrum.
② Unorganized crude drugs (Acellular)
These crude drugs are not made of cells and do not have a cellular structure. They are obtained from plants or animals as secretions. They are also known as acellular crude drugs.
Examples:
- Gums - Acacia, Tragacanth.
- Resins - Asafoetida, Benzoin, Myrrh.
- Latex - Opium, Papain.
- Dried extracts - Agar, Pectin.
Advantages:
- This type of classification is more convenient (easy) for practical purpose.
- Even if chemical characters are not known drugs can be studied for pharmacognostic character.
- Useful for identification of adulterants.
- Crude drug from plant origin can be easily distinguished (source of drug).
- Does not require trained or skilled person.
- It gives idea whether it is organized or unorganized.
Disadvantages:
- Some drug does not express morphological character, hence difficult to classify them clearly.
- But operations like collection, drying, preparation for the market make some changes in crude drug which make recognition difficult.
- Morphological characters do not reflect chemical composition and biological behaviours of crude drugs.
- Repetition of drug occurs.
- Animal drugs and minerals are difficult to classify this method.
3. Pharmacological Classification
Grouping of drug 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 strophan-thus having cardiotonic action are grouped irrespective of their parts used or phylogenetic relationship or the nature of phytoconstituents they contain.
Advantages:
- Classified, even if their exact contents are unknown.
- Used for suggesting substitutes of drugs, if they are not available at a particular place or point of time.
Disadvantages:
- This method does not give any idea of source of drugs.
- Drugs with multiple actions can cause confusion by fitting into more than one group, like Cinchona, which is antimalarial (quinine) but also affects the heart (quinidine).
4. Taxonomical or Biological Classification
The drugs are classified according to the plant or animal from which they are obtained in kingdom, phylum, class, order, family, genus and species.
Carolus Linnaeus is considered as the Father of Taxonomy.
This method is based on natural relationship among plant or animal. A large number of plant families have certain distinguishing characteristic, which permit that crude drug belongs to which family.
Group of organisms with similar characteristics are categorized into species. Species are distinguished based on the morphological characters. For example, different types of mangoes belong to one species.
Advantages:
- Systemic, precise and ordered arrangement of drug.
- Animal drug are classified as fishes, orthopods, mammals, etc.
- Helpful for studying evaluation and development.
Disadvantages:
- Restricted to crude drug from plant origin.
- Unable to distinguished organised and unorganised nature of crude drugs in their morphological study.
- Minerals get excluded from this classification.
- Most of crude drugs don\\\\\\\\\\\\\\\'t represent whole plant or animal.
- No correlation between chemical constituent and biological activity.
5. Chemical Classification
Crude drugs are divided into different groups according to the chemical nature of their most important constituent present in the drug to which the pharmacological/therapeutic activity of drug is attributed. Depending upon the active constituents, the crude drugs are classified.
- Alkaloids - Cinchona, Datura, Vinca, Ipecac Nux vomica
- Glycosides - Senna, Aloe, Ginseng, Glycyrrhiza, Digitalis
- Carbohydrates and its derived products - Acacia, Tragacanth, Starch, Isabgol
- Volatile oil - Clove, Coriander, Fennel, Cinnamon, Cumin
- Resin and Resin combination - Benzoin, Tolu Balsam, Balsam of peru
- Tannins - Catechu, Tea
- Enzymes - Papain, Caesin, Trypsin
- Lipids - Beeswax, Kokum butter, Lanolin
Advantages:
- Same chemical containing drug placed in same class.
- If we know chemical constituent. It is easy to study the drug.
- It is a popular approach for phytochemical studies.
Disadvantages:
- This method does not give any idea about source of drug.
- Ambiguities arise when particular drugs possess a number of compounds belonging to different groups of compounds. Some drugs contain two important chemicals so it is difficult to classify them. Example:- Nutmeg contains volatile oil as well as fat. Cinchona contains glycosides as well as alkaloid.
- No idea whether drug is organized or unorganized.
6. Chemo-taxonomical Classification
Chemotaxonomy is a scientific discipline that uses chemical characters to elucidate taxonomic relationships between organisms. In the context of crude drugs, this classification system combines the traditional taxonomic approach (based on morphological and anatomical features) with the chemical analysis of their constituents.
Benefits:
- Improved Accuracy: Combines chemical and morphological traits for precise classification.
- Evolution Insights: Reveals evolutionary links between plant groups.
- Drug Discovery: By focuses on identifying unique chemical compounds associated with specific taxonomic groups
For example:
- Solanaceae (Nightshade Family): Tropane Alkaloids, Steroidal Alkaloids.
- Fabaceae (Legume Family): Isoflavones, Alkaloids, Tannins
- Apocynaceae (Dogbane Family): Indole Alkaloids, Cardiac Glycosides
The character most often studied in chemotaxonomy are secondary metabolites of pharmaceutical significance such as alkaloids, glycosides, flavonoids, etc.
It is the latest system of classification that gives more scope for understanding the relationship between chemical constituents, their biosynthesis and their possible action