DISCUSSION
In this study of 22,890 elderly persons beginning therapy with antipsychotic medications, patients for whom conventional agents were prescribed had a 37 percent higher, dose-dependent risk of death in the short term than those for whom atypical agents were prescribed. To place this magnitude of risk in perspective, only cancer, congestive heart failure, and HIV infection conferred greater adjusted risks in our analyses. Unfortunately, there are few studies of death associated with drugs in the elderly with which to compare our results; one observational study found higher rates of death among those given a conventional drug (haloperidol) than among those given one of two atypical drugs (risperidone or olanzapine).27 If confirmed, our results suggest that conventional antipsychotic medications may not be safer than atypical agents and should not simply replace atypical drugs that are stopped in response to recent FDA warnings, as may be happening.7
It is important to assess whether methodologic limitations, rather than true biologic relationships, might explain these findings. Confounding would occur if conventional drugs were more likely than atypical agents to be given to patients who were more frail or at greater risk of dying than others. Therefore, using traditional multivariate, propensity-score, and instrumental-variable techniques, we controlled for the demographic and clinical factors and use of health care services that were likely to be independent predictors of death.14-17 We also restricted our analyses to only those patients who had used antipsychotic agents as well as to those who were new users, to control for the underlying reasons that patients use antipsychotic medications and for any selection bias from early emergence of symptoms, drug intolerance, or treatment failure among those already using antipsychotic medications.13
Because authorities4,9-12,28 have recommended avoiding the use of conventional antipsychotic medications for frail elderly persons, any residual confounding may have led to an underestimation of mortality resulting from the use of conventional agents. Any misclassification of exposure status that occurred nondifferentially with respect to the class of antipsychotic agent (e.g., a lack of consumption of filled prescriptions or a switch from a conventional to an atypical antipsychotic agent, or vice versa) would bias results toward the null; differential misclassification (e.g., decreased adherence among patients taking conventional agents, as has been found29) may have led to an underestimation of the rates of death associated with conventional agents. Misclassification of information from Medicare with regard to mortality is less likely, given the Social Security Administration's extensive verification process for data from the Death Master File,21 and such misclassification would presumably bias our findings toward the null.
Finally, we controlled for calendar time, to adjust for any improvements in health care over the study period that could lead to improved survival in later years, when the use of atypical drugs would be more common. However, in spite of these safeguards and the convergence of results from confirmatory and sensitivity analyses, it is important to keep in mind that our study is based on nonexperimental data. There may be other factors with regard to patients who were newly prescribed conventional antipsychotic medications that we were unable to control for, requiring a circumspect interpretation of these findings.
Potential mechanisms through which conventional antipsychotic medications might increase the risk of death in the short term are unclear, and the causes of death were unavailable. In the FDA analysis on which the April 2005 advisory was based, heart-related events (e.g., heart failure and sudden death) and infections (mostly pneumonia) accounted for most deaths.6 Anticholinergic properties (affecting blood pressure and heart rate), prolongation of the QT interval (causing conduction delays), and extrapyramidal symptoms (causing swallowing problems) are at least as common with conventional drugs as with atypical agents, and probably more so, and should be investigated as potential underlying causes of death.4,9-12 Whatever the underlying cause or causes are, they most markedly elevate the risk of death with the use of conventional as compared with atypical antipsychotic medications immediately after the initiation of therapy, after which their influence subsides somewhat.
The hazard ratios associated with conventional as compared with atypical agents were not confined to high-risk elderly persons with dementia or those residing in nursing homes. However, because the clinical trials that the FDA initially reviewed exclusively involved patients with dementia, more data are needed on the absolute risk of death associated with atypical antipsychotic agents in elderly persons who do not have dementia. Our results suggest only that conventional antipsychotic medications do not appear to be safer than atypical agents in populations of elderly persons without dementia.
If confirmed, our results suggest that conventional antipsychotic medications should be included in the FDA's Public Health Advisory, which currently warns only of the increased risk of death with the use of atypical antipsychotic drugs in elderly persons who have dementia. Beyond arousing new concern about conventional agents, our data provide no guidance with regard to which pharmacologic or nonpharmacologic interventions should be used to manage the many conditions and symptoms for which antipsychotic medications are used.4 Traditionally, the benefits and risks of treatments in the elderly have simply been extrapolated from studies involving younger populations.9-12 As the recent FDA advisory and the results of this study show, such a practice can be misleading, given the unique needs and susceptibilities of older persons. Well-designed studies specifically involving the elderly are sorely needed to define optimal care.