Smoking impact on CYP1A2 activity in a group of patients with schizophrenia

The purpose of the present study was to assess the impact of smoking on the metabolism of psychotropic drugs in a group of patients with schizophrenia, by measuring CYP1A2 activity. This activity was assessed by the molar ratio (MR) of caffeine metabolites in urine [(AFMU+1U+1X)/17U] and saliva (17X/137X). Participants were 40 patients with schizophrenia: 30 current cigarette smokers and 10 nonsmokers. The two groups (smokers and nonsmokers) differed significantly in their ratio of men to women (83% men and 17% women were among smokers compared with 50% men and 50% women nonsmokers). No other group differences were found regarding age, level of education, PANSS, extrapyramidal symptoms, age of symptoms onset, antipsychotic doses (chloropromazine equivalents), and anticholinergic drug used. Smokers had significant higher MR in urine (P<0.001) as well as in saliva (P=0.001) than nonsmokers, suggesting a higher activity of CYP1A2 dependent on smoking. When gender was used as a covariate, the differences between the two groups remained significant for MR. Cigarette smoking may be a factor influencing the plasma levels of antipsychotics that metabolized through CYP1A2. Clinicians should weight the possibility that smoking and the subsequent modulation of antipsychotic metabolism may be the main reason of treatment resistance. Furthermore, any attempt to reduce or cease smoking in patients with schizophrenia necessitates close monitoring of drug doses, because untoward adverse effects may emerge.