Increased antipsychotic sensitivity in elderly patients: evidence and mechanisms

The primary objective of this article is to review the literature regarding clinical effects, pharmacokinetics, and pharmacodynamics of antipsychotics in older people and to examine potential mechanisms underlying the age-related antipsychotic sensitivity.

Data for this review were identified by searches of PubMed (1950-2007) and references from relevant articles and books. Search terms included antipsychotic, neuroleptic, elderly, aging, pharmacokinetics, pharmacodynamics, and dopamine, and only articles written in English or Japanese were consulted.

Studies, reviews, and books pertaining to the clinical effects, pharmacokinetics, and pharmacodynamics with regard to the use of antipsychotics in older patients were selected.

The prevailing practices and clinical guidelines suggest that elderly patients can obtain therapeutic benefits at a lower dose and experience adverse effects from antipsychotics more often than younger patients, although there are still few trials that have directly compared elderly patients with the young. The literature suggests an age-related increase in brain access of drugs and demonstrates a decrease with age in the principal components in the dopaminergic system, including endogenous dopamine level and dopamine receptor density.

While clinicians conclusively hold that patients become more sensitive to antipsychotics as they become older, this proposition has only modest empirical support and warrants further investigation. Age-related functional decline in the dopaminergic system predicts lower antipsychotic doses for older patients. We propose a hierarchical series of testable hypotheses to address the relative contribution of age-related pharmacokinetic and pharmacodynamic changes to antipsychotic drug sensitivity.