A person who metabolises a probe drug–the rate of which is related to the metabolising cytochrome P-450 enzyme–slower than others; a person can be a poor metaboliser of one probe drug, and an extensive metaboliser of another.
Examples, poor metaboliser genes
• CYP2C19–which metabolises xenobiotics, including mephenytoin, omeprazole, diazepam, proguanil, propranolol, citalopram, imipramine and some barbiturates
• CYP2D6–which metabolises environmental chemicals and up to 20% of commonly prescribed drugs, including antiarrhythmics, adrenoceptor antagonists, and tricyclic antidepressants.
Frequency, poor metabolisers 2-5% of Caucasians; 13-23% of Asians, 38-79% of Polynesian and Micronesian islanders.