Lithium use in older adults is associated with increased prescribing of Parkinson’s medications

Objectives — To test the hypothesis that there is an increased incidence of antiparkinson drug prescribing or Parkinson's disease diagnostic codes following chronic lithium treatment, compared to chronic valproic acid or antidepressant treatment among older adults.

Design — A retrospective cohort study using healthcare administrative databases.

Setting — Ontario, Canada

Participants — 1,749 lithium users, 1,787 valproic acid users and 285,154 other antidepressant users 66 years of age or older, having used the drug continuously in monotherapy for at least one year.

Outcome Measures — 1) The start of a dopaminergic medication (levodopa or a dopamine agonist), 2) The start of any antiparkinson drug (levodopa, dopamine agonists, anticholinergic medication, amantadine, monoamine oxidase B inhibitors), 3) the start of any antiparkinson drug OR a diagnostic code for Parkinson's disease and 4) the start of any antiparkinson drug in the absence of a diagnostic code for Parkinson's disease.

Results — For patients with no previous antipsychotic use, lithium monotherapy was associated with an increased incidence of dopaminergic drug use (adjusted HR 1.87, 95% CI 1.06-3.30) and an increased incidence of antiparkinson drug use OR a Parkinson's disease diagnosis (adjusted HR 1. 68, 95% CI 1.13-2.48) compared to antidepressant monotherapy.

Conclusions — Chronic lithium use is associated with an increased incidence of dopaminergic drug use compared with antidepressants, identifying a prescribing cascade related to lithium use in the elderly. Whether this reflects inappropriate treatment of action tremor or treatment of drug-induced parkinsonism should be addressed by a close examination of prescribing practices.