General Principles of Mechanism of Action of Drugs

Pharmacodynamics vs. Pharmacokinetics

Understanding how drugs interact with biological systems is fundamental to pharmacology. Two major concepts define this interaction: pharmacodynamics and pharmacokinetics.

Pharmacodynamics

Pharmacodynamics refers to the effects of drugs on the body and the mechanisms by which they exert their action.

• Receptor Binding: Drugs typically act by binding to specific receptors on cells.
• Dose-Response Relationship: The effect of a drug increases with its concentration, up to a saturation point.
• Therapeutic and Toxic Effects: All drugs have both beneficial and potentially harmful effects.

Pharmacokinetics

Pharmacokinetics describes how drugs are absorbed, distributed, metabolized, and excreted from the body.

• Absorption: The process by which a drug enters the bloodstream.
• Distribution: How the drug is transported through body fluids to target sites.
• Metabolism: The biochemical transformation of a drug, usually in the liver.
• Excretion: The removal of the drug and its metabolites, primarily via the kidneys.

Key Differences

Aspect	Pharmacodynamics	Pharmacokinetics
Definition	Effect of drug on body	Effect of body on drug
Major Components	Receptor binding, dose-response, therapeutic effects	Absorption, distribution, metabolism, excretion

Conclusion

Both pharmacodynamics and pharmacokinetics play a crucial role in determining the efficacy and safety of drugs. A thorough understanding of these principles helps healthcare professionals optimize drug therapy.