Background: The relative risk of diabetes among patients undergoing risperidone treatment was compared with that of patients receiving olanzapine.
Method: A cohort was formed of 33,946 patients with at least 1 prescription for either olanzapine (N = 19,153) or risperidone (N = 14,793) between January 1, 1997, and December 31, 1999, recorded in the Régie de l'Assurance Maladie du Québec database. Patients were excluded if clozapine was dispensed to them during the study period or if they were diagnosed with diabetes before beginning antipsychotic therapy. New diabetes diagnoses made after the first antipsychotic prescription during the period were tabulated until December 31, 1999; censoring occurred at this date or at the last service date, if there was no record of using services during the last 6 months of follow-up. Crude hazard ratio and proportional hazard analyses were carried out.
Results: 319 patients developed diabetes on olanzapine treatment, and 217 developed diabetes on risperidone treatment; a crude hazard ratio of 1.08 (95% CI = 0.89 to 1.31, p =.43) was determined. When age, gender, and haloperidol use were controlled for using proportional hazard analysis, there was a 20% increased risk of diabetes with olanzapine relative to risperidone (95% CI = 0% to 43%, p =.05). Proportional hazard analyses adjusted for duration of olanzapine exposure indicated that the first 3 months of olanzapine treatment was associated with an increased risk of diabetes of 90% (95% CI = 40% to 157%, p <.0001), after adjusting for age, gender, and haloperidol use.
Conclusion: Compared with risperidone, olanzapine was associated with an increased risk of developing diabetes. More studies are required to further investigate this association.