Nature of Drugs

Nature of Drugs refers to the physical, chemical, and biological properties of drugs that determine their action, effectiveness, and therapeutic use.

Definition of a Drug:

• A drug is any substance (natural or synthetic) that, when administered to a living organism, produces a biological effect.
• Drugs are used for diagnosis, prevention, treatment, or cure of diseases.

Chemical Nature of Drugs

1. Organic vs. Inorganic

   • Organic: Most drugs are organic compounds (carbon-based), often containing nitrogen, oxygen, sulfur.
   • Inorganic: Some drugs are made of metal ions or salts (e.g., lithium carbonate, magnesium sulfate).

2. Acids and Bases

   • Most drugs are weak acids or weak bases.
   • Their ionization affects absorption, distribution, and excretion.
   • Ionized (charged) drugs are water-soluble but poorly lipid-soluble → poor absorption.
   • Non-ionized (uncharged) drugs are lipid-soluble → better absorption.

3. Physical States

   • Drugs may exist as:
     • Solids: Tablets, capsules, powders.
     • Liquids: Syrups, emulsions.
     • Gases or volatile liquids: Anesthetics like nitrous oxide.

4. Stereoisomerism

   • Some drugs have optical isomers (enantiomers) with different biological activities.
   • Example: L-isomer of propranolol is active; D-isomer is less active.

5. Prodrugs

   • Inactive compounds that become active after metabolic conversion inside the body.
   • Example: Enalapril (inactive) → Enalaprilat (active).

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