Enzyme induction and inhibition

Enzyme induction is a process in which a molecule (e.g. a drug) induces (i.e. initiates or enhances) the expression of an enzyme. Enzyme inhibition refers to the inhibition of an enzyme by a molecule. These terms are of particular interest to pharmacology, and more specifically to drug metabolism. They also apply to molecular biology.

If the molecule induces enzymes that are responsible for it's own metabolism, this is called auto-induction (or auto-inhibition if there is inhibition).

One class of key enzymes for drug metabolism belong to the family of cytochrome P450 oxidases, like cyp3A4, cyp2D6, cyp1A2, etc.

Enzyme induction and inhibition are important processes to take in account when using drugs of vital importance to the patient, drugs with important side effects and drugs with small therapeutic windows, but any drug may be subject to an altered plasma concentration due to altered drug metabolism.

A classical example includes anti-epileptic drugs. Phenytoïne, for example, is metabolised by cyp2C19 and cyp2C9, but also induced these enzymes. Therefore, tolerance is expected to develop rapidly.