NCMA216 (Pharmacodynamics)

Pharmacodynamics

The study of what the drug does to the body: the mechanism of drug actions in living tissues.

Onset

Time it takes for the drug to elicit a therapeutic response.

Peak

Time it takes for a drug to reach its maximum therapeutic response.

Duration

Time a drug concentration is sufficient to elicit a therapeutic response.

Mechanisms of Action

Drugs modify the rate at which cells or tissues function, but cannot make them do new functions.

Agonist

Drug binds to receptor and activates it (“lock and key”).

Antagonist

Drug binds but blocks the receptor (“denied”).

Competitive Inhibition

Agonist and antagonist compete for the same receptor.

Non-competitive inhibition

Antagonist binds at a different site and blocks receptor.

Drug-Receptor Interactions

Drug and receptor binding involves physicochemical and steric interactions: lipophilic, hydrophilic, ionic, hydrogen bonds, steric, electronic, pK effects.

Signaling Pathways

Drug-receptor interactions trigger cascades via second messengers (Ca²⁺, Na⁺, K⁺, Cl⁻, cAMP, cGMP, IP3, DAG).

Law of Mass Action

Magnitude of response is proportional to fraction of receptors occupied; binding is reversible.

Adverse Drug Reaction (ADR)

Any noxious, unintended, undesired effect at doses used in humans (WHO).

Idiosyncratic Reaction

Unusual/abnormal reaction due to genetic defect (inability to metabolize).

Allergic

Immune system reaction after prior exposure (antibodies formed).

Anaphylactic

Severe life-threatening allergic reaction causing respiratory distress and collapse.

Carcinogenicity

Drug induces cells to mutate and become cancerous.

Teratogen

Drug induces birth defects.

Tolerance

Need higher dose for same effect.

Dependence

Addiction/habituation, can be physical or psychological.

Cumulative Effect

Drug builds up if given before previous dose is eliminated → toxicity.

Placebo

Positive expectation improves outcome, no drug action.

Nocebo

Negative expectation worsens outcome.

Drug Interactions

When one drug alters the action of another (increase or decrease).

Additive

Same effect added.

Synergistic

Stronger together.

Antagonistic

One blocks the other.

Displacement

One drug pushes another off protein.

Interference

First drug inhibits metabolism/excretion of another.

Incompatibility

Drugs chemically clash when mixed.

Pharmacotherapeutics

Use of drugs to prevent and treat diseases; which drug is most/least appropriate and dose required.

Acute Therapy

A kind of therapy that is immediate, short-term.

Maintenance Therapy

A kind of therapy to prevent progression.

Supplemental Therapy

A kind of therapy to provide substance body lacks.

Prophylactic Therapy

A kind of therapy to prevent disease.

Therapeutic Index (TI)

Ratio between a drug’s therapeutic benefits and its toxic effects (TxD50 / ED50).

Adverse drug events

Preventable, due to errors → harm.

Adverse drug reactions

Not preventable, occurs at normal use.