Cytochrome P450-2D6, also known as CYP2D6 or debrisoquine hydroxylase, is a
liver enyme which is extensively involved in metabolizing drugs. Many drugs
are metabolized by P450-2D6, and many drugs also inhibit it. Some people
are genetically lacking in the normal P450-2D6 variant, and physicians will
use DXM to determine which variant of P450-2D6 a patient has (10-11). About
5-10% of Caucasians and 0.5% of Asians seem to lack P450-2D6 entirely, or
have a very inactive mutation (12-15). In remaining individuals, its
activity can vary significantly due to genetic factors (15-18). Between
0.5% and 2% of the population has multiple copies of the P450-2D6 gene and
will metabolize 2D6-dependent drugs much more quickly than most people
(155).
Since many drugs become toxic at high doses, it is important to give the
proper amount to those people who will metabolize it differently than the
normal population. DXM is used to test metabolism by CYP2D6. The patient is
given a specific amount of DXM, and then the relative concentrations of DXM
and its metabolites are determined.
Some recent research suggests that susceptibility to lung cancer may be
related to P450 variant, and DXM may be an effective diagnostic tool for
predicting lung cancer susceptibility (376).
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