Active Principle of Drugs

Active Principles of Drugs

Active principles are the chemically active constituents of crude drugs that produce pharmacological or therapeutic effects.

 1. Alkaloids

• Definition: Basic, nitrogenous compounds, mostly derived from plants.
• Solubility:
  • Insoluble in water
  • Slightly soluble in alcohol
  • Soluble in ether, chloroform, and oils
  • Form water-soluble salts with acids (crystalline salts)
• Pharmacological activity: Usually strong and specific.
• Exception: Epinephrine, an alkaloid from animal source (adrenal medulla).
• Examples:

 2. Glycosides

• Definition: Compounds made of a sugar (glycone) + a non-sugar (aglycone/genin) linked via an ester bond.
• Action:
  • The aglycone part has pharmacological activity.
  • The glycone part affects solubility, absorption, and duration of action.
• Characteristics:
  • Do not form salts with acids.
  • Undergo hydrolysis (acid/alkali/enzyme) → sugar + aglycone.
• Examples: Digitalis glycosides (not listed but commonly cited)

 3. Oils

A. Fixed Oils

• Definition: Glycerides of oleic, palmitic, stearic acids.
• Properties:
  • Non-volatile
  • Used as food or pharmaceutical vehicles
• Uses: Nutritional, laxative, demulcent
• Examples:

B. Volatile Oils (Essential/Aromatic Oils)

• Properties:
  • Volatile, emit strong odour
  • No food value
  • Used medicinally and in flavouring
• Examples: Eucalyptus oil, clove oil (not mentioned in original text but relevant)

 4. Resins

• Definition: Amorphous, brittle products from oxidation/polymerization of terpenes in volatile oils.
• Properties:
  • Insoluble in water
  • Soluble in alcohol and organic solvents
  • Form soaps with alkalis
• Examples:
  • Colophonium
  • Podophyllin

5. Oleoresins and Balsams

A. Oleoresins

• Mixture of volatile oils, gums, and resins
• Example: Asafoetida

B. Balsams

• Subtype of oleoresins containing resin, volatile oil, and aromatic acid
• Examples:
  • Balsam of Tolu
  • Balsam of Peru

6. Gums

• Definition: Polysaccharide secretions from plants.
• Action:
  • Inert systemically
  • Act as demulcents, suspending agents, or emulsifiers
• Examples:
  • Agar
  • Gum acacia

7. Saponins

• Definition: Non-nitrogenous compounds soluble in water.
• Characteristics:
  • Produce foam or froth when shaken with water.
  • On hydrolysis → sugar + sapogenin
  • Considered a subclass of glycosides
• Examples:
  • Quillaja
  • Senega

 8. Tannins

• Definition: Water-soluble, non-nitrogenous plant substances.
• Action:
  • Astringent effect (precipitate proteins)
  • Protective action on mucous membranes (e.g., GI tract)
• Example:
  •  catechu