Module 5: Pharmacodynamics and Pharmacokinetics

Drug-receptor interaction

First step of Mechanism of Drug Action (MOA). It is where a drug must bind with a receptor to produce an action

Drug

Any chemical substance that affects living processes

Receptor

Component of tissue where drug binds; a polymeric structure that recognizes and binds a compound

Ligand

Molecule of complementary shape to protein binding site

Drug-receptor interaction

Interaction between drug and receptor determining drug's action

Structure-activity relationship

Relationship between chemical structure and pharmacological activity

Quantitative aspect of interaction

Measurement of drug concentration at receptor and response magnitude

Biophase

Immediate vicinity of site of action where drug concentration is effective

Graded dose-response relationship

Increased dose leads to increased intensity of response

Quantal dose-response relationship

Increased dose leads to greater number of animals showing all-or-none response; more drug dose = more number of animal exhibiting increased response

ED50

Median effective dose; dose that will produces response in 50% of the animal population

LD50

Median lethal dose; dose that causes death in 50% of population

Agonist

A drug that binds receptor and causes a change leading to an effect

Antagonist

Drug that counteracts the effect of an agonist

Pharmacologic antagonist

Inhibits agonist by interacting with receptor or any part of the effector

Competitive antagonist

Competes for the same receptor with the agonist

Non-competitive antagonist

Inhibits agonist from producing the effect at a given receptor site, that also inhibits any part of the stimulus.

Allosteric agonist

This drug bind to a different region of the receptor

Chemical/Physiologic antagonist

Counters agonist effect by chemical reaction, not receptor binding

Protamine

Basic drug that neutralizes acidic drug Heparin

Affinity

Tendency of a drug to bind to a specific receptor

Efficacy (Intrinsic activity)

Maximal effect a drug can produce

Selectivity

Ability to produce specific effect at lower dose

Specificity

When all effects of drug are via one mechanism

Potency

Dose needed to produce a given intensity of effect

Therapeutic Index (TI)

LD50 / ED50; measures drug safety

Certain Safety Factor (CSF)

LD1 / ED99; stricter measure of safety

Paracelsus Principle

"The dose makes the poison"

Down-regulation

Chronic receptor stimulation → receptor desensitization

Up-regulation

Chronic receptor under-stimulation → receptor hypersensitivity

Drug targets

Protein molecules: enzymes, carriers, ion channels, receptors

Allostery

Protein's ability to change shape upon ligand binding

Drugs not requiring receptor binding

Inhalant anesthetics, osmotic diuretics, saline cathartics, antacids, urinary acidifiers, antiseptics