Background — Differences between atypical antipsychotics in their potential to cause parkinsonism and risk factors for antipsychotic-induced parkinsonism are not well established. There is a particular paucity of information on this in real-world use of these drugs, outside of clinical trial settings.
Objective — The researchers compared the incidence of parkinsonism after new treatment with risperidone, olanzapine, or quetiapine in patients with dementia and examined the effects of dose and sex on the risk of parkinsonism.
Methods — Administrative data from Ontario, Canada between 2002 and 2010 were used to compare the incidence of a diagnostic code for parkinsonism or prescription of an anti-Parkinson medication among patients with dementia who were newly prescribed quetiapine, olanzapine, or risperidone.
Results — From 15,939 person-years of observation, 421 patients developed parkinsonism. Using low-dose risperidone as the reference group, the adjusted hazard ratios for developing parkinsonism were 0.49 (95% CI, 0.07–3.53) for low-dose olanzapine and 1.18 (95% CI, 0.84–1.66) for low-dose quetiapine. Comparing across drugs within the most commonly prescribed dose ranges, the incidence of parkinsonism was higher in the medium-dose olanzapine group compared with the low-dose risperidone group (hazard ratio 1.66; 95% CI 23–2.23). The adjusted hazard ratio for developing parkinsonism for men (compared with women) was 2.29 (95% CI, 1.88–2.79).
Conclusions — The researchers found no evidence that the risk of drug-induced parkinsonism in older adults with dementia was different among quetiapine, olanzapine, or risperidone, challenging the notion that the drugs differed in their propensity to cause parkinsonism. Men appeared to be at higher risk of parkinsonism as a adverse event than women.