Changing prescription patterns for lithium and valproic acid in old age: shifting practice without evidence

Methods and results

We obtained information on drug use from the Ontario Drug Benefit Program, which provides comprehensive drug benefits to all residents aged 65 or older in Ontario, Canada. We identified all patients who had been taking lithium or valproic acid between 1993 and 2001 (prevalent users) and we further identified those patients who had not previously taken lithium or valproic acid (new users). We restricted our study to patients aged 66 or more to enable us to examine their previous drug use for a minimum of one year. Using unique encrypted health card numbers, we linked data on this cohort to two other large datasets—the Canadian Institute for Health Information dataset of all hospital separations and the Ontario Health Insurance Plan dataset of all claims for physician services. These datasets provided information on hospitalisations and visits to physicians that helped us distinguish between psychiatric and anticonvulsant uses of lithium and valproic acid and between bipolar disorder and other indications such as dementia.

New elderly users of valproic acid and lithium who did not have a diagnosis of dementia before the incident use, Ontario, 1993-2000

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Among patients who had no previous history of convulsive disorders, we identified 3902 patients who had started taking lithium and 5341 patients who had started taking valproic acid between 1993 and 2001. New valproic acid users were slightly older than lithium users (75.4 years v 73.5 years). More than three quarters of new lithium users and fewer than two thirds of valproic acid users had contact with a psychiatrist. Almost one quarter of the new lithium patients and 41% of new valproic acid users had had a diagnosis of dementia.

The number of new lithium users per year fell from 653 older adults in 1993 to 281 in 2001, whereas the number of valproic acid users rose from 183 in 1993 to 1090 in 2001. The trend was similar when we eliminated patients who had had a diagnosis of dementia (figure). The number of new valproic acid users surpassed new lithium users in 1997, with a steady decline in new lithium users and a steady increase in new valproic acid users between 1993 and 2000.

Comment

Prescription patterns have shifted in favour of valproic acid over lithium, for elderly patients with bipolar disorder. This shift is occurring in the absence of evidence based data. Lithium carbonate has been a mainstay for the management of bipolar disorders for all age groups, but elderly patients pose a special concern because of the potential for toxicity.4 Before the use of lithium is abandoned for these patients, however, adequate evidence that valproic acid offers a comparable or superior efficacy, effectiveness, and safety profile is needed. Indeed, the concerns about lithium toxicity may reflect a failure to adjust for pharmacokinetic and pharmacodynamic factors that occur in old age.4 For example, renal clearance changes notably with age, and hence also lithium clearance. Better guidelines for dosage and serum concentrations of lithium carbonate for elderly people are needed before clinicians switch to prescribing new agents, especially with the associated risk of relapse that follows the discontinuation of lithium.5 Given the complexity, morbidity, and mortality associated with bipolar disorders and dementia in elderly patients, the use of mood stabilisers and other psychotropic agents requires ongoing systematic evaluation.