CYP induction

CYP induction is the mirror image of inhibition: instead of jamming the metabolic machinery, a drug makes the body build more of it. It is as if heavy traffic prompted the city to open extra toll lanes — now everything that uses those lanes gets processed faster. A co-administered drug that relies on the same enzyme is then cleared more quickly and its levels fall.

The mechanism is genetic rather than chemical: certain compounds activate nuclear receptors such as PXR or CAR, which switch on the genes that encode P450 enzymes (and some transporters and conjugating enzymes). Over days to a couple of weeks the cell synthesizes more enzyme protein, raising overall metabolic capacity. Because it depends on new protein synthesis, induction sets in slowly and reverses slowly after the inducer is stopped.

Induction matters because it can quietly cause a drug to fail. If an inducer lowers the blood level of a critical co-medication — say an oral contraceptive, an immunosuppressant, or an anticoagulant — the patient may lose efficacy without obvious warning. Strong inducers like rifampicin and certain anticonvulsants are well known, and developers test whether new candidates activate the relevant nuclear receptors.