Incidence of delirium in older adults newly prescribed lithium or valproate: a population-based cohort study.
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.


METHODS
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).


CONCLUSIONS
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.
Shulman
Kenneth I
KI
Department of Psychiatry and the Institute for Clinical Evaluative Sciences, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Ontario, Canada. ken.shulman@sw.ca
Sykora
Kathy
K
Gill
Sudeep
S
Mamdani
Muhammad
M
Bronskill
Susan
S
Wodchis
Walter P
WP
Anderson
Geoffrey
G
Rochon
Paula
P
D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D000927:Anticonvulsants / Q000009:adverse effects* / Q000627:therapeutic use; D000928:Antidepressive Agents / Q000009:adverse effects* / Q000627:therapeutic use; D001590:Benztropine / Q000009:adverse effects / Q000627:therapeutic use; D015331:Cohort Studies; D003693:Delirium / Q000139:chemically induced* / Q000453:epidemiology*; D011307:Drug Prescriptions / Q000706:statistics & numerical data; D017723:Drug Utilization Review / Q000706:statistics & numerical data; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D016651:Lithium Carbonate / Q000009:adverse effects* / Q000627:therapeutic use; D019964:Mood Disorders / Q000188:drug therapy* / Q000523:psychology; D020258:Neurotoxicity Syndromes / Q000453:epidemiology; D009864:Ontario / Q000453:epidemiology; D016016:Proportional Hazards Models; D016896:Treatment Outcome; D014635:Valproic Acid / Q000009:adverse effects* / Q000627:therapeutic use
D000927:Anticonvulsants; D000928:Antidepressive Agents; D001590:Benztropine; D016651:Lithium Carbonate; D014635:Valproic Acid