Effect of smoking on neuroleptics in schizophrenia

Objective: The effect of smoking on daily doses and plasma levels of neuroleptics prescribed for schizophrenic patients was studied. Methods: 90 outpatients with schizophrenic disorder (DSM-III-R) who were on a stable regimen of psychotropic medication and showed a stable clinical state were included in a double-blind placebo-controlled trial. Data were collected and blood tests taken at the baseline interview. The plasma levels were obtained for 52 patients. Results: Daily neuroleptic doses converted to chlorpromazine equivalents correlated significantly (r=0.436) with the plasma levels of their unmetabolised fractions. The neuroleptic doses increased with age in smokers, while in nonsmokers they decreased. Neither sex, age nor smoking had a significant association with the neuroleptic plasma levels. Conclusions: Smoking seems to lead to increased neuroleptic dosages in postmenopausal schizophrenics by increasing hepatic metabolism and renal excretion of the drugs and possibly enhancing dopamine release. It is also possible that older smoking patients form a selected group of heavy smokers and they, therefore, need exceptionally high neuroleptic doses.