http://www.pharmacytimes.com/publicatio ... 07-11-8279
Assessing CYP1A2 Activity in Patients
For some CYP450 enzymes such as CYP2D6, genetic factors dictate most of the activity of the enzyme, and genotyping of patients may be useful. This is not true for CYP1A2, however, where the activity of the enzyme is dictated largely by environmental, dietary, and other factors in addition to genetics.1 In this case, phenotyping is more useful, where, instead of genetic testing, a probe compound is given to the patient and the actual enzyme activity is determined. One proposed phenotyping method for CYP1A2 is to obtain a saliva sample following a test dose of caffeine. One drawback of such testing is that the subject must abstain from coffee, many teas and soft drinks, and chocolate for a day or so before the test.
The enzyme CYP1A2 increasingly is involved in drug interactions as new medications metabolized by this enzyme are released. Some of the substrates that warrant particular attention are theophylline, clozapine, olanzapine, and tizanidine. Some of the more potent CYP1A2 inhibitors include cimetidine, ciprofloxacin, enoxacin, and fluvoxamine. Among CYP1A2 inducers, smoking is probably the most important, but the usual enzyme inducers such as rifampin and barbiturates can also substantially increase CYP1A2 activity.