A special nomenclature has been developed to identify these enzymes. CYP, the designate of the system, is followed by an arabic number to designate the family, followed by a capital letter for the subfamily, and finally an arabic number again for the gene 1 . When a substrate drug is exposed to these modified CYP450 enzymes, that drug can accumulate to toxic levels in the face of a paralyzed CYP450 system. Alternatively, a drug can be metabolized so rapidly by the primed CYP450 enzymes that it becomes ineffective or less active due to its rapid elimination. 3 Metabolic inhibition can be either competitive or noncompetitive.
Competitive inhibition is the more common with reversible inhibition at the enzyme's site.
Once the enzyme is inhibited, the return to action of the enzyme is dependent upon the half-life of the inhibiting drug. The free amiodarone molecules have to be cleared from the blood before the competitively bound molecules can be released and become active. Chloramphenicol is such an inhibitor of CYP2C9. This pattern of inhibition is much less common. The priming or induction of a CYP enzyme also relies on the half-life of the inducing drug.