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Clinical Pharmacology

Pharmacokinetics, pharmacodynamics, and drug mechanisms

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pk_pd_petra 23 terms Dec 25, 2025
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Terms 23

1
Pharmacokinetics (PK)
What the body does to the drug: Absorption, Distribution, Metabolism, Excretion (ADME)
2
Pharmacodynamics (PD)
What the drug does to the body: receptor binding, mechanism of action, effects
3
Bioavailability (F)
Fraction of administered drug reaching systemic circulation; oral < IV (100%)
4
First-Pass Effect
Metabolism in gut wall and liver before reaching systemic circulation; reduces oral bioavailability
5
Volume of Distribution (Vd)
Hypothetical volume drug would occupy if uniformly distributed; Vd = dose/plasma concentration
6
Half-Life (t₁/₂)
Time for plasma concentration to fall by half; t₁/₂ = 0.693 × Vd / CL
7
Clearance (CL)
Volume of plasma cleared of drug per unit time; CL = dose / AUC
8
Steady State
Rate in = rate out; reached after ~4-5 half-lives of continuous dosing
9
Loading Dose
Large initial dose achieving therapeutic concentration rapidly; LD = Vd × Cp_target
10
Therapeutic Index
LD₅₀/ED₅₀; ratio of toxic to effective dose; wide TI = safer drug
11
EC₅₀
Concentration producing 50% of maximum effect; measure of drug potency
12
Emax (Efficacy)
Maximum possible effect of a drug regardless of dose; ceiling effect
13
Agonist
Binds receptor and activates it; full agonist achieves maximum response
14
Partial Agonist
Binds and activates receptor but with lower Emax; acts as antagonist in presence of full agonist
15
Inverse Agonist
Binds receptor and reduces baseline activity below constitutive level
16
Competitive Antagonist
Blocks agonist binding; shifts dose-response right; same Emax; overcome by more agonist
17
Irreversible Antagonist
Binds covalently; reduces Emax; cannot be overcome; e.g. aspirin, phenoxybenzamine
18
CYP450 Enzymes
Liver enzymes metabolizing most drugs; CYP3A4 most abundant; inducers/inhibitors cause interactions
19
Drug-Drug Interactions
Enzyme induction (reduces levels) or inhibition (increases levels); transport competition
20
Renal Clearance
Filtration + secretion − reabsorption; reduced in renal failure; dose adjustment needed
21
Receptor Upregulation
Chronic antagonist → more receptors; withdrawal causes exaggerated response (rebound)
22
Receptor Downregulation
Chronic agonist → fewer receptors; tolerance; requires higher dose for same effect
23
Tachyphylaxis
Rapid decrease in response to drug after repeated doses; acute form of tolerance