Incidence of Delirium in Older Adults Newly Prescribed Lithium or Valproate: A Population-Based Cohort Study
J Clin Psychiatry 2005;66(4):424-427
© Copyright 2014 Physicians Postgraduate Press, Inc.
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Background: The use of lithium carbonate for the
treatment of mood disorders in old age has decreased at a
dramatic rate in favor of valproate. Because of lithium's narrow
therapeutic range, neurotoxicity can be an important complication
in lithium therapy and potentially influence prescription
patterns. Therefore, we compared the incidence of delirium in
older adults with mood disorders who were newly dispensed either
lithium or valproate.
Method: Using 4 population-based administrative
databases from the province of Ontario, Canada (the Ontario Drug
Benefit program, the Canadian Institute for Health Information,
the Ontario Health Insurance Plan, and the Registered Persons
Data Base), we were able to identify a cohort of mood disorder
patients 66 years and older who were newly dispensed lithium or
valproate over an 8-year period (1993-2001). Measures were taken
to ensure that the sample was composed of mood disorder patients.
As a comparator, we included a known deliriogenic drug,
benztropine. The main outcome measure was a new diagnosis of
delirium on a hospitalization record during 1 year of follow-up.
Results: Our study cohort consisted of 2422 new
users of lithium and 2918 new users of valproate over an 8-year
period. There was no statistically significant difference in the
incidence of delirium between lithium (2.8 per 100 person-years)
and valproate (4.1 per 100 person-years). Compared with patients
who received lithium, patients who received benztropine had a
significantly higher risk of delirium (p < .001).
Conclusion: The incidence of hospitalizations
with delirium was similar in patients treated with lithium and
valproate. These findings add to the evidence suggesting that the
shift away from the use of lithium carbonate to manage mood
disorders in older adults is not justified on the basis of
concerns of neurotoxicity.