MichaelisMenteneliminointi

Michaelis‑Menten elimination is a kinetic model used to describe the rate at which a substrate—or in pharmacokinetics, a drug—is removed from a biological system. The model originates from the classical Michaelis‑Menten equation that characterises enzyme‑catalysed reactions. In the elimination context the rate of decrease of the compound concentration is expressed as

V = (Vmax · C)/(Km + C)

where C is the instantaneous concentration, Vmax is the maximal elimination rate when the metabolising system is saturated, and Km is the concentration at which the elimination rate is half of Vmax.

At low concentrations the equation simplifies to first‑order kinetics because C ≪ Km, giving V ≈ (Vmax/Km) C. As concentration rises, elimination becomes saturated and the rate approaches Vmax, making the process zero‑order. This behaviour is especially relevant for drugs metabolised by hepatic enzymes such as CYP450 isoforms, or for substances excreted by saturable transporters in the kidney.

The model is applied in pharmacokinetic modelling, dose‑regimen design, and toxicity studies. It provides a more realistic description than simple first‑order elimination for drugs with high therapeutic doses. However, the Michaelis‑Menten elimination assumes a single, non‑regenerating enzyme mechanism and neglects phenomena such as induction, inhibition, or transporter competition. When multiple pathways contribute to elimination, a composite model combining first‑order and Michaelis‑Menten terms may be required.