Antipsychotic and antidepressant drug use in the elderly and the risk of venous thromboembolism

BACKGROUND: Preliminary evidence suggests that use of antipsychotic drugs is associated with an increased risk of venous thromboembolism. OBJECTIVE: To evaluate the relationship between antipsychotic or antidepressant drug use and venous thromboembolism among adults aged 65 years and older. DESIGN: Retrospective cohort study using linked health care administrative databases over a nine year period. SETTING: The entire province of Ontario, Canada. PARTICIPANTS: Individuals aged 65 years and over exclusively prescribed either antipsychotic drugs (n = 22,514), antidepressant drugs (n = 75,649) or thyroid replacement hormones (33,033), the referent control group. We excluded those with an antecedent history of cardiovascular disease, venous thromboembolism or cancer, as well as those dispensed warfarin before study entry. MEASUREMENTS: Diagnosis of deep vein thrombosis or pulmonary embolism. RESULTS: Relative to those prescribed thyroid hormones, neither antidepressant (adjusted hazard ratio 1.02, 95% CI 0.91-1.14) nor antipsychotic (adjusted hazard ratio 1.13, 95% CI 0.96-1.32) drug use was associated with an increased risk for deep vein thrombosis. Similar risk estimates were found for deep vein thrombosis or pulmonary embolism. In a sub-group analysis, only butyrophenone use was found to be associated with a slightly increased risk of deep vein thrombosis (adjusted HR 1.51, 95% CI 1.23-1.86) as well as deep vein thrombosis or pulmonary embolism (adjusted HR 1.43, 95% CI 1.18-1.74). CONCLUSIONS: In a large cohort of adults aged 65 years and older, neither antipsychotic or antidepressant drug use was associated with an increased risk of venous thromboembolism, with the exception of a slightly increased risk among those prescribed butyrophenones. Further data are required before use of these psychoactive drugs can be considered a risk factor for venous thromboembolism.