Circadian Changes in Drug Metabolism

Diurnal variations have been reported for several microsomal drug metabolism activities mediated by the cytochrome p-450 mixed function oxidase systems . The oxidative reaction catalysed by the cyctochrome p-450 monooxygenase system are the major pathways involved in the disposition of drugs and toxic chemical agents.
Hence, any chronobiological variations, in the rate of these processes may modify the pharmacokinetics of drugs whose body clearance is directly related to hepatic velocity of oxidative reactions.
Also as these biotransformations are responsible for the first pass elimination of drugs the bioavailability of drugs subjected to first pass effect may get affected by the time dependent variations of these liver processes.