Inherited variability in the pharmacokinetics of drugs due to lower level or absence of an enzyme can affect the metabolic rate and the metabolic profile of some drugs.
Rapid/slow acetylators: The rate of isoniazid metabolism depends on acetylator phenotype of the individual. Rapid acetylators eliminate isoniazid much faster than slow acetylators.
{
Rapid Acetylator
{
Slow Acetylator
The rate of isoniazid metabolism
is faster and the amount of the
acetyl metabolite formed is larger
in rapid acetylators.
Poor metabolizers (abnormal CYP2D6): The amount of morphine formed after administration of codeine is significantly smaller in individuals with abnormal CYP2D6. Patients with abnormal CYP2D6 experience lower analgesic effect after codeine administration.
Codeine plasma conc-time profile is
not different in the two populations
since lower CYP2D6 does not affect
the overall disposition rate of codeine.
This is because only 10% of codeine.
dose is metabolized by CYP2D6.
Morphine plasma conc is lower in
patients with lower CYP2D6 level
because smaller fraction of codeine
dose is converted to morphine.
