Prevalence of diabetes and impaired glucose tolerance in patients treated with clozapine compared with patients treated with conventional depot neuroleptic medications

Background: Recent case reports suggest the association of the emergence of diabetes mellitus with clozapine treatment, although conventional neuroleptics have also been implicated. This study was conducted to determine if there is an increased risk of diabetes mellitus and/or impaired glucose tolerance (IGT) during clozapine treatment compared with treatment with conventional depot neuroleptics. Method: In a district hospital in northern Sweden, blood glucose tests and, if necessary an oral glucose tolerance test were used to assess the prevalence of diabetes mellitus or IGT in 63 patients treated with clozapine compared with 67 patients treated with conventional depot neuroleptics (haloperidol, zuclopenthixol, fluphenazine, perphenazine, or flupenthixol). Diabetes mellitus and impaired glucose tolerance were classified according to World Health Organization criteria. Results: There were 3 dropouts in the clozapine group and 4 in the control group. Of subjects treated with clozapine, 12% (7/60) had type 2 diabetes mellitus, and 10% (6/60) had IGT. Of subjects treated with depot injections of neuroleptics, 6% (4/63) had type 2 diabetes mellitus and 3% (2/63) had IGT. None in either group had type 1 diabetes mellitus. Subjects in the clozapine group were significantly (p <.001) younger than subjects in the control group, whereas the 2 groups did not differ with respect to body weight, body mass index, or prevalence of diabetes mellitus in first-degree relatives. Conclusion: Subjects treated with clozapine were more often classified as having type 2 diabetes mellitus or IGT compared with subjects in the control group. This difference did not, however, achieve statistical significance (p =.06).