Part 3: Pharmacodynamics

What the Drug Does to the Body

Pharmacodynamics (PD) describes the relationship between drug concentration and pharmacological effect. It encompasses drug-receptor interactions, signal transduction, and the dose-response relationship that determines therapeutic outcomes.

$$E = \frac{E_{max} \cdot [D]}{EC_{50} + [D]}$$

Emax model: Effect as a function of drug concentration

Topics in This Part

3.1 Drug-Receptor Interactions

Binding kinetics, affinity, selectivity, specificity

3.2 Dose-Response Relationships

Graded vs quantal, potency, efficacy, therapeutic index

3.3 Agonists & Antagonists

Full/partial agonists, competitive/noncompetitive antagonists, inverse agonists

3.4 Receptor Theory

Occupancy theory, two-state model, spare receptors, constitutive activity

3.5 Signal Transduction

Second messengers, kinase cascades, amplification, crosstalk

3.6 Tolerance & Desensitization

Receptor downregulation, tachyphylaxis, dependence, withdrawal

Agonist Types

Full Agonist

Produces maximal response (efficacy = 1)

Partial Agonist

Submaximal response even at full occupancy

Inverse Agonist

Reduces constitutive receptor activity

Neutral Antagonist

Blocks receptor without affecting basal activity

← Part 2: Pharmacokinetics3.1 Drug-Receptor →