Classification of drugs
As per PCI Syllabus

(S. Y. B. Pharm Sem –IV)  Unit-I



1. Alphabetical classification :


It is the simplest way of classification of any disconnected items. Crude drug are arranged in Alphabetical order of their Latin and English names (Common names) or sometimes local.

Some of the pharmacopoeias, dictionaries and reference books which classify crude drugs according  to this system are as follows:

1.Indian Pharmacopeia
2.British Pharmacopeia
3.British herbal Pharmacopeia
4.United States Pharmacopeia & National Formulary
5. British pharmaceutical Codex.
6.European Pharmacopeia

Notes: No. (1, 2, 3, 4) these are arranged in English, (6) arranged according to
their names in Latin Advantages If we know the name of drug, we Can study it
properly.

2. Morphological classifications:

are mainly based on the arrangement of crude drugs according to the parts used
as a source of drug.

If the crude drug is constituted by definite tissue structures, then these drugs
are classified as organized drugs and if the crude drug is not composed of
definite cell structure are classified as unorganized drugs (eg. Asafoetida,
Benzoin, Catechin Acacia, Honey etc.).

Organized drugs can be classified as the crude drugs obtained as leaves, barks,
wood, herbs, roots, rhizomes, seeds or fruits, flowers or flower buds etc.


Some examples of Organized drugs

Leaves : Senna, Digistalis, tea, vasaka, vinca, eucalyptus etc.
Barks    : Cinnamon, cassia, cascara, cinchona, quillaia
Woods  : Sandal. Quassia etc.
Flower  : Saffron, rose, jasmine, pyrethrum
Seeds   : Linseed, nutmeg, isapgol, Almond etc.
Fruits   : Cardamom, orange, fennel, caraway, pepper etc.
Herbs  : Ephedra, tulsi etc.
Roots and rhizomes : Liquorice, turmeric, rauwolfia, jalap, jatamansi, asparagus, aswagandha, ipecae etc.

Examples for some unorganized drugs are

Dried latex  : Opium, papain

Dried juices : Aloes, red gum
Dried extracts : Alginates, Gelatin
Gums     : Acacia, tragacanth
Resins    : Asofetida, benzoin, jalap, myrrh
Fats      : Lard
Wax     : Bees wax, wool fat, spermaceti
Fixed oil : Castor oil, ground nut oil, coconut oil, etc.

Advantages
1. It is more convenient for practical purpose.
2. Even if the chemical content or action of drug is not known the drug can be studied properly.
3. It gives idea about source of drugs.
4. It gives idea whether it is organized/ unorganized.
Disadvantages

During collection, drying & packing morphology of drug changes. They are difficult to study.

3. Taxonomic Features

The plants belong to a particular family, in most of the situations exhibit similar taxonomic characters like the type of fruits, inflorescence, type and arrangement of flowers, leaves etc.

Taxonomists usually faces  another problem in finding out similarities of characters in unrelated plants (called as convergence in taxonomy) and some times related plants used to exhibit dissimilarities in their characters (known as divergence).

Another term in taxonomy attracting the attention of taxonomists is parallelism. This indicates the similarity in the evolutionary characters of related plant or plant groups. Some interesting examples of plant families in which the member of a family exhibiting similar botanic characters but seems to show dissimilarities in their active constituents and therapeutic uses are

Taxonomical classification is purely a botanical classification, it's based on principles of natural relationship & evolutionary developments.
They are grouped in ( Kingdom, Phyllum, Order, Family, Genus & Species ).

E. g. Fennel
Division - Angiosperm.
Class - Dicotyledonac.
Order- Umbelliflorae.
Family- Umbelliferae.
Example- Fennel.
Disadvantage

No idea about organized /unorganized

4. Pharmacological Classification

In this system 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 followed method.

Drugs like digitalis, squill and strophanthus having cardiotonic action are grouped together irrespective of their parts used or phylogenetic relationship or the nature of phytoconstituents they contain.

The drugs having similar pharmacological effect in body are grouped together.

Pharmacological Action Drug

1. Carminatives: Fennel, Dill, Coriander, and Clove.
2. Purgatives: Cascara- sagrada, Aloe, Senna & Rhubarb.
3. Cardio tonics: Digitalis, squill, and strophanthus.
4. Anthelmintic : Artemisia, Male- fern, and Quassia.
5. Anti- cancer : Podophyllum, Vinca,
6. CNS Stimulant: Nuxvomica.
7. Expectorant: Vasaka, Liquoric.
8. Bitter tonic: Gentian, Cinchona, and Nux vomica.

Disadvantages

1. Some crude drugs have two different pharmacological actions therefore it is difficult to classify them.
E.g. Nux vomica is CNS stimulant as well as bitter tonic. Cinchona is bitter tonic as well as Antimalarial & Antipyretic.
2. Drugs that have different mechanism of action have to be grouped together.
e. g. Castor oil is irritant purgative & lsapgol is bulk purgative but they are placed in one group.
3. No idea whether drugs are organized or unorganized
4. This method does not give any idea of source of drugs.

Advantages

If we know pharmacological action it is easy to study the drug.

5. Chemical Classification

The crude drugs are divided into different groups according to the chemical nature of their most important constituent. Since the pharmacological activity and therapeutic significance of crude drugs are based on the nature of their chemical constituents.

The chemical classification of drug is dependent upon the grouping of drugs with identical constituents. An out of this classification is as follow:

1. Carbohydrates
Carbohydrates are polyhydroxy aldehydes or ketones containing an unbroken chain of carbon atoms.
Gums - Acacia, Tragacanth.
Mucilages- Plantago seed.
Others - Starch, Honey, Agar, Pectin, Cotton.

2. Glycosides

Glycosides are compounds which upon hydrolysis give rise to one or more sugars (glycone) and non sugar (aglycone).

Anthraquinone Glycosides -Aloe, Cascara, Rhubarb, Senna.
Saponins Glycosides -Quillaia, Glycyrrhiza.
Cyanophore Glycosides - Wild cherry bark.
Isothiocyanate Glycosides - Mustard.
Cardiac Glycosides - Digitalis, Strophantus.
Bitter Glycosides - Gentian, Calumba, Quassia.

3. Tannins:

Tannins are complex organic, non-nitrogenous derivatives of polyhydroxy benzoic acids.
Ex: Pale catechu, Black catechu, Ashoka bark, Galls, Amla.

4. Volatile Oils

Monoterpines & Sesquiterpenes obtained from plants.
Ex: Cinnamon, Fennel, Dill, Caraway, Coriander, Cardamom, Orange peel. Mint, Clove, Valerian.

5. Lipids

Fixed oils - Castor, Olive, Almond, Shark liver oil.
Fats - Theobroma, Lanolin.
Waxes -Beeswax.

6. Alkaloids
Nitrogenous substance of plant origin.
Pyridine and Piperidine - Lobelia, Nicotiana.
Tropane - Coca, Belladonna, Datura, Stramonium,
Quinoline - Cinchona.
Isoquinoline - Opium, Ipecac, Calumba.
Indol - Ergot, Rauwolfia.
Amines - Ephedra.
Purine - Tea, Coffee.

7. Resins

Complex mixture of compounds like resinols, resin acids, resinotannols, resenes.
Ex: Colophony, Podophyllum, Cannabis, Capsicum, Turmeric, Balsam of Tolu and Peru, Myrrh, Ginger.

8. Protein

Gelatin, Ficin, Papain.

9. Vitamins

Yeast.

10. Triterpines

Rasna, Colocynth.

Disadvantages
1. This method does not give any idea about source of drug.
2. Some drugs contain two important chemicals so it is difficult to classify them.
e.g. Nutmeg contains volatile oil as well as fat. Cinchona contains glycoside as well as alkaloid.
3. No idea whether drug is organized or unorganized.
Advantages

If we know chemical constituent. It is easy to study the drug.

6. Chemo - Taxonomical Classification

This system of classification relies on the chemical similarity of 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.

Similarly plant metabolites can serve as the basis of classification of crude drugs.
The berberine alkaloid in Berberis and Argemon, Rutin in Rutaccae members, ranunculaceous alkaloids among its members etc are examples.

It is latest system of classification and gives more scone for understanding the relationship between chemical constituents, their biosynthesis and their possible action.

Serotaxonomy classification:

The application or utility of Serology in solving taxonomic problems is called as Serotaxonomy.

Serology mainly concentrates on the study of the precipitation reactions between antigen and antibodies. The substance capable of stimulating the formulation of an antibody is called an antigen and the highly specific protein molecule produced by plasma cells in the immune system is called as antibody.
The antibodies combine chemically with specific kind of antigens.

Proteins are the substances useful for carrying taxonomic information's and the same are the most widely used antigens in serotaxonomy.

As a summary, serological studies are used for the following purposes.

This expresses similarities and dissimilarities among different taxa and these data are helpful in taxonomy. It determines the degree of similarities between species, genera, families etc. by comparing the reactions of antigens from various plant taxa with antibodies developed against the antigen.

This study helps in comparing non-morphological characteristics; the knowledge of which is useful in taxonomy.

Single protein from different plant taxas are also compared by serology techniques.

General features of serological reaction

The reaction is specific, an antigen is combining only   with it’s homologous antibody.
Entire molecules react and not the fragments.
Combination occurs at the surface and it is firm but   reversible .
Antigens and antibodies can combine in varying   proportions.
Both antigens and antibodies take part in the formation   of precipitates or agglutinates.

General process of serotaxonomy

Mainly in this studies, the protein extract of plant or animal origin i.e., antigen is injected into the blood stream of a rabbit or an experimental animal, form the antibodies. In response to a specific antigen a specific antibody is produced. 

The serum called antiserum is then made to react in vitro with the antigenis protein as well as with proteins of other taxa, the affinities of which are to be determined. The amount of precipitation shows the degree of the proteins homology one would like to ascertain the closeness of a taxon A with B, C and D.

The proteins extracted from A are injected into a rabbit in which the antibodies are produced. The antibodies are then extracted from the blood of rabbit in the form an antiserum. When the antiserum is allowed to react with the original protein extract from A, a total coagulation takes place when the antiserum is allowed to react with the protein extracts from the taxa B, C and D the degree of coagulation is related directly to the closeness between taxa being compared. 

Methods of serotaxonomy

1.Gel diffusion method
2.Slide precipitation method
3. Petridish  method