Pharmacodynamics
Pharmacodynamics relates drug exposure to a biological or clinical effect.
Emax model
A common saturating concentration–effect relationship is
\[E(C)=E_0+\frac{E_{\max}C}{EC_{50}+C},\]where \(E_0\) is baseline effect, \(E_{\max}\) the maximum additional effect and \(EC_{50}\) the concentration giving half of \(E_{\max}\).
Link with pharmacokinetics
Pharmacokinetics supplies the time-dependent concentration \(C(t)\); pharmacodynamics maps that concentration to an effect \(E(t)\).
Key idea. Pharmacodynamics models what a drug does to the biological system, whereas pharmacokinetics models how drug exposure changes through time.