Pharmacology Definition and Scope

Pharmacology Definition and Scope

• Pharmacology studies drugs and their interactions with living systems.
• The term originates from Greek: "pharmacon" (drug) and "logos" (study).
• A drug is a substance used to diagnose, prevent, or treat diseases.
• The World Health Organization (WHO) defines a drug as something used to modify or explore physiological systems or pathological states.

Drug Sources

• Drugs originate from natural or synthetic sources.
• Natural Sources: Plants (e.g., atropine, morphine, quinine), animals (e.g., insulin, heparin), minerals (e.g., magnesium sulfate, iron), microorganisms (e.g., penicillin, tetracycline), and humans (e.g., immunoglobulins, growth hormone).
• Synthetic Sources: Most modern drugs are synthesized (e.g., quinolones, omeprazole). Others are obtained from cell cultures or through recombinant DNA technology (e.g., human insulin) or hybridoma technology (e.g., monoclonal antibodies).

Pharmacokinetics

• Pharmacokinetics studies drug absorption, distribution, metabolism, and excretion (ADME) – essentially, how drugs move within the body.
• Drug movement involves crossing biological barriers (intestinal epithelium, cell membranes, renal membranes, capillary barriers).
• Biotransport refers to drug movement across barriers.
• Transport Mechanisms: Passive diffusion (high to low concentration, no energy required); Carrier-mediated transport (facilitated diffusion – high to low, no energy; active transport – against concentration gradient, energy required); Pinocytosis (cell drinking); Phagocytosis (cell engulfing particles).

Passive Diffusion

• Movement of drug molecules from high to low concentration without energy expenditure.

Carrier-Mediated Transport

• Polar compounds and some drugs use carrier proteins to cross membranes.
• Facilitated diffusion is carrier-mediated transport from high to low concentration without energy use. GLUT 4 is an example facilitating glucose transport.

Pinocytosis and Phagocytosis

• Pinocytosis: Cell engulfs fluid containing drugs (e.g., insulin crossing the blood-brain barrier).
• Phagocytosis: Cell engulfs particles (e.g., botulinum toxin poisoning).

Routes of Drug Administration

• Drug administration routes depend on drug properties and patient needs.
• Routes are broadly categorized as enteral, parenteral, and local.

Enteral Route (Oral Ingestion)

• The most common, safest, and oldest route.
• Advantages: Safest, convenient, economical, self-administrable, non-invasive
• Disadvantages: Slower onset, unsuitable for irritants/unpalatable drugs, potential for gastric irritation/vomiting, some drugs are destroyed by gastric juices (e.g., insulin).