Drug Structures and Mechanisms

Study Notes

Drug Definition and Origin

The term "drug" originates from "Drogue," meaning ‘a dry herb.’
WHO defines a drug as a substance used to modify physiological processes for the recipient's benefit.
All drugs are considered poisons, but not all poisons qualify as drugs.

General Features of Drugs

Molecular Size: Smaller molecules are absorbed more easily; ideal molecular weight is between 100-1000 Da (e.g., streptokinase: 47,286.7 Da vs. nitric oxide: 30.01 Da).
Shape: Drugs can be globular or linear, modifying their shape based on receptor interaction. Examples include pH and temperature-responsive polymeric drugs.
Chemical Nature: The pharmacophore is essential for optimal interactions with biological targets, influencing drug efficacy (e.g., different effects of benzoic acid vs. 5-chloro salicylic acid).
Lipid/Water Partition Coefficient (log P): Lipid soluble drugs are retained in the body, while water-soluble drugs are more readily excreted.
Degree of Ionization: Ionized drugs are polar and water-soluble, whereas unionized drugs are less polar and lipid-soluble; ions can pass through specific channels.
Physical Properties: Drugs can exist as solids, liquids, or gases. Gas diffusion rates surpass those of liquids and solids.

Drug Effects

Local Effect: Occurs at the site of application, affecting specific tissues.
Systemic Effect: Drug action spreads throughout the body, typically via bloodstream circulation.

Mechanisms of Drug Action

Molecular Level: Drug action involves ion channels, enzymes, and carrier molecules (e.g., aspirin inhibits COX).
Cellular Level: Interaction with cell types, such as smooth muscle cells (e.g., calcium channel blockers).
Tissue Level: Effects include contraction, secretion, and metabolic activity (e.g., salbutamol's bronchodilation).
System Level: Alters functions at central and peripheral nervous systems (e.g., atorvastatin reducing LDL cholesterol).

Drug Action Mechanisms

Ligand-Gated Ion Channels (LGIC): Open following ligand binding, allowing ion flow and altering membrane potential within 0.1 – 2 milliseconds.
G-Protein Coupled Receptors (GPCR): Activation of G-proteins modifies ion channel states and influences cellular processing, including protein expression changes.

Description

Explore the fundamental concepts of drug structures and their mechanisms in this informative quiz. Gain insights into how the general structure of a drug affects its physiological and pathological interactions. Perfect for pharmacy students and professionals alike.