Part 2: Pharmacokinetics
What the Body Does to the Drug
Pharmacokinetics (PK) describes the time course of drug concentration in the body. The acronym ADME summarizes the four key processes: Absorption, Distribution, Metabolism, and Excretion.
$$\frac{dC}{dt} = \frac{F \cdot D \cdot k_a}{V_d} \cdot e^{-k_a t} - k_e \cdot C$$
One-compartment model with first-order absorption and elimination
Topics in This Part
2.1 Absorption (ADME)
Routes of administration, bioavailability, first-pass effect
2.2 Distribution
Volume of distribution, protein binding, tissue barriers
2.3 Metabolism
Phase I/II reactions, cytochrome P450, enzyme induction/inhibition
2.4 Excretion
Renal clearance, hepatic clearance, half-life, steady state
2.5 Pharmacokinetic Models
One/two-compartment models, non-compartmental analysis, population PK
2.6 Drug Interactions
PK interactions, enzyme inhibitors/inducers, clinical significance
Key PK Parameters
Bioavailability (F)
Fraction of drug reaching systemic circulation
$F = \frac{AUC_{oral}}{AUC_{IV}}$
Volume of Distribution (Vd)
Apparent volume drug distributes into
$V_d = \frac{Dose}{C_0}$
Clearance (CL)
Volume of plasma cleared per unit time
$CL = k_e \cdot V_d$
Half-Life (t₁/₂)
Time to reduce concentration by 50%
$t_{1/2} = \frac{0.693 \cdot V_d}{CL}$