In Reply We agree with Gnjidic and colleagues that it is important to consider pharmacologic factors, including dose, drug interactions, and individual drug effects, when conducting pharmacoepidemiologic studies in older persons. The Drug Burden Index (DBI) has been one metric proposed to account for the composite burden of sedatives and anticholinergic drugs.1 While this index considers pharmacologic factors such as dose and specific drug interactions, it assumes that similar drugs have identical pharmacodynamic and pharmacokinetic effects in all individuals.1 To the degree that this assumption is violated, bias from misclassification of exposure is introduced. Furthermore, analyses with the DBI may be difficult for clinicians to interpret because they do not provide specific information on the dose and drug of concern.
Berry SD, Dore DD. Understanding Drug Effects in Older People: The Role of Pharmacology—Reply. JAMA Intern Med. 2013;173(20):1930–1931. doi:10.1001/jamainternmed.2013.9762