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Older antipsychotic drugs may be at least as risky for elderly dementia patients as newer medications, a study says.

The authors of the study suggest until further evidence is available, doctors should proceed with caution when prescribing either type of antipsychotic drug to elderly patients.

The work, by researchers from Harvard Medical School and the University of British Columbia, backs up a previous study the same group published last year in the New England Journal of Medicine. The new study was published in this week's Canadian Medical Association Journal.

In mid-2005, health regulators in Canada and the United States warned that second generation antipsychotic drugs – called atypical antipsychotics – seemed to raise the risk of death when taken by seniors suffering from dementia. Studies had shown that elderly patients newly prescribed these drugs had a 1.6 greater death rate than patients taking a placebo.

Drugs included in these studies were risperidone (Risperdal), quetiapine (Seroquel) and olanzapine (Zyprexa). A fourth in this class, clozapine (Clozaril), was not studied. But because it is in the same family, Health Canada included it in its warning about the potential risks of atypical antipsychotics.

The authors of this study concluded the warnings about the newer antipsychotics might have prompted doctors to revert to using conventional antipsychotic medication in this patient population, drugs like chlorpromazine (Largactil, Thorazine), haloperidol (Haldol) and loxapine (Loxapac, Loxitane).

So they set out to study if the older drugs were also associated with an increased risk of death.

Using patient data from British Columbia, the authors compared 12,882 people over age 65 taking the older drugs to 24,359 seniors taking the atypical drugs. Within the first six months of treatment, 14.1 per cent of the people on the conventional drugs died, compared to 9.6 per cent in the atypical antipsychotics group.

“In these analyses, the adjusted risk difference . . . meant that, for every 100 patients prescribed a conventional antipsychotic drug instead of an atypical drug, there were about four additional deaths,” they wrote.

Reasons for the increased risk of death aren't clear, they note, though some evidence points to increased risk of heart-related conditions, impact on blood pressure and swallowing problems as potential explanations.