Pharmacognosy: Crude Drugs, Classification, and Uses

Posted on Jan 26, 2025 in Biology

Pharmacognosy

Pharmacognosy is defined as the scientific and systematic study of structural, physical, chemical, and biological characters of crude drugs, along with their history, method of cultivation, collection, and preparation for the market.

Sources of Crude Drugs

1) Plant Source: Neem, Babul, Tulsi, Saffron, Clove.
2) Animal Source: Honey bee, beeswax, Silk, Insulin, Shark liver oil, Thyroid.
3) Mineral Source: Chalk, bentonite, asbestos, talc, kaolin, Fuller’s earth.
4) Micro-Organism: Antibiotics.
5) Marine: Salt, Protozoa, etc.

History of Pharmacognosy

Egyptians were aware of the medicinal uses of several plants and animals and also about human anatomy.
The Greek physician Hippocrates (460- 360 B.C.), known as the ‘Father of Medicine’.
Aristotle, the renowned philosopher (384 – 322 B.C.), is well known for his studies on the animal kingdom, and Theophrastus (370 – 287 B.C.) for the plant kingdom.
Pedanius Dioscorides (040- 080 A.D.), a Greek physician, in 78 A.D. described several plants of medicinal importance in “De Materia Medica”.
The Indian history of medicinal plants dates back to 3500 B.C. The curative properties of plants have been mentioned in the Suktas of Rigveda and Atharvaveda.
Ayurveda has also described a good number of plants with their therapeutic properties. The ancient, well-known treaties in Ayurveda, the Charak Samhita and Susruta Samhita, were written by Charka and Susruta, respectively.

Scope

1 Analysis and Phytochemicals: Many bioactive biomolecules are extracted and isolated from crude drugs.
They are analyzed by modern techniques such as Thin Layer Chromatography (TLC), High-Performance Liquid Chromatography (HPLC), and Gas Chromatography.
2 Herbal Preparation Herbal Medicine: Herbal medicines have become more popular in recent years because it is believed that these do not have any toxins or side effects compared to modern medicine.
3 Flavoring Agents and Perfumes: A large number of aromatic plants are extensively used as flavoring agents, perfumes, spices, and medicine, e.g., Ajowan, Lemongrass, etc.
4 Tissue Culture: Plant tissue culture broadly refers to the in-vitro cultivation of plant seeds and various parts of the plants: organs, embryos, tissues, single cells, and protoplasts.

Classification of Drugs

  • Alphabetical classification.
  • Taxonomical classification.
  • Morphological classification.
  • Pharmacological classification.
  • Chemical classification.
  • Chemo-taxonomical classification.
  • Serotaxonomical classification.

Alphabetical Classification

Alphabetical classification is the simplest way of classification of any disconnected or alphabetically similar crude drugs.

Taxonomical Classification

In this classification, drugs are classified based on their division, class, subclass, order, family, genus, and species. It is a type of biological classification and is restricted mainly to crude drugs from plant sources.

Morphological Classification

In this type of classification, crude drugs are divided into the parts of plants like leaves, fruits, flowers, woods, barks, extracts, gums, etc.

Pharmacological Classification

In this classification, drugs are placed together that show similar pharmacological functions or therapeutic effects.

Chemical Classification

In this classification, crude drugs are put together that contain similar chemical constituents.

Chemo-taxonomical Classification

This classification combines the two classifications for defining crude drugs, in which we investigate the drug category and chemical composition. Many crude drugs contain chemical constituents that belong to similar classes or are closely related to similar species, families, or divisions.

Serotaxonomical Classification

This technique is based on the highly specific relationship between antigens and the antibodies produced in response to the animal during any infection or harm.

Adulteration of Crude Drugs

Adulterations are defined as the admixture of genuine articles with spurious or harmful substances.

Methods of Adulterating Drugs

A. Substitution with Manufactured Materials: This is done with artificially manufactured materials that resemble various drugs in form and appearance. Example: Paraffin wax has been colored yellow to substitute beeswax.
B. Substitution with Inferior Material: Drugs are sometimes adulterated and substituted with standard commercial materials. The common example of substitution is the adulteration of cloves with mother cloves.
C. Substitution with Exhausted Material: Exhausted materials are the vegetable residues that remain after the original material has been used for drug preparation. Examples include the substitution of Alexandrian Senna with Arabian Senna and the use of exhausted Clove and ginger for adulteration.
D. Substitution with Cheap Natural Substances: Sometimes, drugs are adulterated with cheaper natural substances that have no relation to the genuine article. Examples include Japan wax for beeswax and sterculia gum for Tragacanth.
E. Adulteration with Non-Plant Material: Plant materials are sometimes adulterated with worthless non-plant materials.

Standardization of Crude Drugs

The different techniques involved in the standardization of crude drugs are as follows:
1. Physical Evaluation: Physical standards are to be determined for drugs wherever possible. They may help in evaluation, specifically with reference to specific gravity, density, optical rotation, refractive index, melting point, viscosity, and solubility in different solvents.
2. Chemical Evaluation: Chemical evaluation comprises different chemical tests and chemical assays. The isolation, purification, and identification of active constituents are chemical methods of evaluation. Quantitative chemical tests such as acid value and saponification value also help in the proper identification of various crude drugs.
3. Biological Evaluation: The estimation of the potency of crude drugs is done by means of its effect on living organisms like bacteria, fungal growth, animal tissue, or entire animals; it is called a bioassay. Bioassay is the measure of the sample being tested capable of producing the biological effects as that of the standard preparation.

Alkaloids

Based on the chemical nature of alkaloids, they are divided into three parts:
A. True Alkaloids: True alkaloids derive from amino acids, and they share a heterocyclic ring with nitrogen. These alkaloids are highly reactive substances with biological activity even in low doses. The primary precursors of true alkaloids are such amino acids as L-ornithine, L-lysine, L-tryptophan, and L-histidine. Examples of true alkaloids include such biologically active alkaloids as cocaine, quinine, dopamine, and morphine.
B. Proto/Amino Alkaloids: Protoalkaloids are compounds in which the nitrogen atom derived from an amino acid is not a part of the heterocyclic ring. Such kinds of alkaloids include compounds derived from L-tyrosine and L-tryptophan. Examples include hordenine, mescaline, and yohimbine.
C. Pseudo Alkaloids: Pseudoalkaloids are compounds, the basic carbon skeletons of which are not derived from amino acids. These alkaloids can also be derived from non-amino acid precursors. Examples include coniine, capsaicin, ephedrine, solanidine, caffeine, and theobromine.

Identification Tests for Alkaloids

1. Mayer’s Reagent (Potassium Mercuric Iodide Solution): Take the alkaloid materials → Mix with Mayer’s reagent → then a cream-colored precipitate is obtained.
2. Wagner’s Reagent (Solution of Iodine in Potassium Iodide): Take the alkaloid materials → Mix with Wagner’s reagent → then a brown or reddish-brown precipitate is obtained.
3. Hager’s Reagent (Saturated Solution of Picric Acid): Take the alkaloid materials → Mix with Hager’s reagent → then a yellow-colored precipitate is obtained.
4. Dragendroff’s Reagent (Potassium Bismuth Iodide): Take the alkaloid materials → Mix with Dragendroff’s reagent → then a reddish-brown precipitate is obtained.
5. Murexide Reagent (Ammonium Purpurate): Take the alkaloid materials → Mix with the murexide reagent → then a purple-colored precipitate is obtained.

Therapeutic/Pharmaceutical Applications of Alkaloids

In therapeutic efficiency, alkaloids are used at a broad level.
  • Acts on CNS: Depressants (Morphine), stimulants (Caffeine).
  • Acts on ANS: Sympathomimetic (Ephedrine), Parasympathomimetic (Pilocarpine), Anticholinergic (Atropine, Hyoscyamine).
  • Local anesthetic or analgesics (Cocaine and Morphine).
  • Antitumor (Vinblastine).
  • Antimalarial (Quinine).
  • Antibacterial (Berberine).
  • Antiseptic (Scopolamine).

Glycosides

A glycoside is any molecule in which a sugar group/moiety is bonded through its anomeric carbon to another group via a glycosidic linkage. Chemically, glycosides are acetals in which the hydroxyl of the sugar is condensed with a hydroxyl group of a non-sugar component.

Identification Tests for Glycosides

1. Borntrager’s Test (Anthraquinone Glycoside): Take 1g of crude drugs → Then add 5-10ml of HCl and boil on a water bath for 10 minutes and filter → Filtrate was extracted with CCl4/Benzene and add an equal amount of ammonia solution and shake well → Formation of a pink or red color in the ammonia layer due to the presence of anthraquinone glycoside.
2. Saponin Glycoside: Take the crude drug on a slide → Then add some drops of blood and mix well → RBCs become ruptured due to the presence of saponin glycosides.
3. Steroid Glycoside: Take alcoholic crude drugs and mix with CHCl3 → Slowly add concentrated H2SO4 from the side walls of the test tube → A yellow-colored ring appears at the junction of two liquids, which turns red after 2 minutes, indicating the presence of steroids.
4. Vanillin HCl Test for Flavonoid Glycoside: Take alcoholic crude drugs and mix with vanillin HCl → Formation of a pink color due to the presence of flavonoids.
5. Killer-Killani Test for Cardiac Glycoside: Take alcoholic drug + an equal amount of water and add 0.5ml of strong lead acetate solution, shake well, and filter → An equal amount of chloroform is added to the filtrate and evaporated to dryness → Then the residue is dissolved in 3ml of glacial acetic acid followed by the addition of a few drops of FeCl3 salt → Finally, the solution is transferred into a 2ml concentrated H2SO4 test tube → A reddish-brown layer is formed, which turns bluish-green after standing due to the presence of digitoxose.

Therapeutic/Pharmaceutical Applications of Glycosides

  • Senna Leaves: Senna leaves are used as a laxative. It causes irritation of the large intestine and has some griping effect. Senna is a stimulant cathartic and exerts its action by increasing the tone of the smooth muscles in the large intestine.
  • Aloe: The drug Aloes is one of the safest and most stimulating purgatives; in higher doses, it may act as an abortifacient. Its action is exerted mainly on the large intestine; also, it is useful as a vermifuge.
  • Digitalis Leaves: It is also used in allopathic medicine in the treatment of heart complaints. It has a profound tonic effect upon a diseased heart, enabling the heart to beat more slowly, powerfully, and regularly without requiring more oxygen.
  • Bitter Almond: It is used as a sedative.

Volatile Oils and Terpenoids

Volatile oils are the odorous chemical substances that easily evaporate when exposed to air at ordinary temperatures. Terpenoids are the hydrocarbons of plant origin of the general formula (C5H8)n, as well as their oxygenated, hydrogenated, and dehydrogenated derivatives.

Identification Tests for Volatile Oils

1. Take the naturally containing volatile oils and treat with an alcoholic solution of Sudan-III; a red color develops in the presence of volatile oil.
2. Take the naturally containing volatile oils and treat with a tincture of alkane, which produces a red color that indicates the presence of volatile oils.
3. Take 0.5ml of eugenol-containing drug and add 2 drops of 1% FeCl3 solution. Then a green color is produced, indicating the Eugenol chemical.

Therapeutic/Pharmaceutical Applications of Volatile Oils/Terpenoids

  • In pharmaceutical formulations, it is used as a flavoring agent and perfuming agent for masking the unpleasant odor of drugs.
  • It is also used in the food, beverage, and cosmetic industries.
  • It shows more therapeutic values: Carminative (Umbelliferous fruits), Irritant (Turpentine and oil of wintergreen), Local anesthetics (Clove), Sedative (Jatamansi), and Anthelmintics (Chenopodium oil).

Tannins

Tannins are secondary metabolites: complex organic, non-nitrogenous, phenolic plant products, which generally have astringent properties.

Identification Tests for Tannins

1. Gold Beater’s Skin Test: Take a gold beater’s skin piece and initially soak in 2% hydrochloric acid and wash with distilled water → Then place in a solution of tannin for 5 minutes, then wash with distilled water and transfer to 1% ferrous sulfate solution → Finally, a brown or black color membrane appears, indicating the presence of tannin.
2. Phenazone Test: Take 5ml of an aqueous solution of tannin and add 0.5g of sodium acid phosphate → Then warm the solution, cool, and filter, and add 2% phenazone solution to the filtrate → Finally, all tannins are precipitated as bulky, colored perceptibly.
3. Gelatin Test: Prepare the gelatinous solution by adding 1% of gelatin solution and a little amount of 10% sodium chloride → Then add a 1% solution of tannin → Finally, tannin causes precipitation of the gelatin solution.
4. Test of Catechin (Match Stick Test)
5. Test for Chlorogenic Acid
6. Vanillin Hydrochloric Acid Test

Therapeutic/Pharmaceutical Applications of Tannins

  • Medically, tannins show astringent properties and promote rapid healing and the formation of new tissue.
  • Tannins are also used for treating wounds and inflamed mucosa.
  • Tannins are used in the treatment of various ulcers, hemorrhoids, minor burns, frostbite, etc.
  • Recently, tannins showed antiviral activities and are used for the treatment of viral diseases, including AIDS.

Resins

Resin can be defined as a complex amorphous chemical of more or less solid characteristics. On heating, they initially soften and finally melt.

Identification Tests for Resins

1. Dissolve about 0.1g of powdered resin in 10ml of acetic anhydride → Then add one drop of cold and concentrated sulfuric acid on a glass rod → After adding the acid, a purple color, rapidly changing to violet, is produced.
2. Take the resinous drug (0.5g), boil with hydrochloric acid (5ml), and filter → Then add ammonia with the filtrate → Finally, a blue fluorescence is obtained.
3. Take the crude resinous drug and add 50% of nitric acid. Finally, a green color is produced.
4. Take the crude resinous drug and add 1 drop of sulfuric acid. Finally, a red color is obtained, which changes to violet on washing with water.
5. The alcoholic solution of balsam reacts with potassium permanganate to yield benzaldehyde.
6. The alcoholic solution of balsam is acidic to litmus paper.

Therapeutic/Pharmaceutical Applications of Resins

The pharmaceutical applications of resins are local irritants, local cathartics (e.g., Jalap, Ipomoea), as anticancer (podophyllum), in bronchial asthma (Cannabis), used externally as a mild antiseptic in the form of tinctures (Benzoin), ointments, and plasters (Turpentine and Colophony), and used in the preparation of emulsions and sustained-release formulations.