Traffic Tech #301: Literature Review of Polypharmacy and Older Drivers: Identifying Strategies to Study Drug Usage and Driving Functioning Among Older Drivers

As the population of the United States ages and the number of older drivers increases, there is growing concern about the effect that taking multiple medications – polypharmacy - has on older peoples’ abilities to drive safely.  The National Traffic Highway Safety Administration (NHTSA) sponsored a literature review to determine if there are practical means to obtain information about drug usage by older drivers under everyday “real-world” conditions that are valid and reliable, and to measure the consequences of multiple drug use for safe driving.  Further goals include identifying candidate methodologies for carrying out such studies that are both cost-effective and likely to be successful in obtaining a diverse and representative sample of older drivers.  TransAnalytics, LLC, identified 1,600 abstracts from current literature (2001-2004) on polypharmacy, drugs, and older drivers. These abstracts were screened and 143 relevant articles on the following topics were reviewed:  identifying medication use; measuring medication adherence; measuring driving performance; and polypharmacy and older people.

Medication/Polypharmacy Effects on Older People

The first section examines recent literature on medication use in community-dwelling older people (those not living in nursing homes or other institutions) in the United States and other countries. This section examines studies on the physiological effects and physiological changes that affect how older people metabolize their medications. This report focused on those medications most frequently used by the older community-dwelling population, such as benzodiazepines, opioids, antidepressants, and anti-diabetics. In addition, this section provides a general overview of medication use and crash risk by examining recently conducted epidemiological and experimental studies to determine the consequences of a single class of medication on the ability to drive safely.  A few studies are reported that examine multiple medication use. However, there is a dearth of research on the effects of combinations of specific medications or even combinations of drug classes on driving ability per se.  Although prescription medications are the major focus of this review, over-the-counter medication use by older people is included where it was reliably documented in the literature. Additional areas that received attention in the literature review on polypharmacy include: how polypharmacy among older adults has an impact on areas other than driving (such as falls), and older people’s use of alcohol in combination with other medications—as alcohol use per se is not the focus of this project. 

Measuring Medication Usage

Since conclusions cannot be made about the effects of medications on driving behavior if the medication is not taken, or more or less of the medication is taken than prescribed, the second section of this review examines the measuring/monitoring of medication usage. This section begins with a discussion of methods used to measure compliance, including the pros and cons of each method. These methods include: clinical judgment, patient’s self-report, clinical response, biochemical measures, pill counts, pharmacy records, and electronic medication monitoring devices. This section also examines the factors affecting compliance with medication regimes. Medication-related factors are when there is a decrease in compliance associated with increases in the complexity, cost, and duration of medication regime, the number of prescribed medications, and the severity of side effects. Patient-related factors that correlate with low compliance include: limited access to health care; financial problems; communication barriers; and lack of social support. The prescriber-related factors that correlate with low compliance include: a poor prescriber-patient relationship; poor prescriber communication skills; a mismatch between the prescriber and patient regarding health beliefs; and a lack of positive reinforcement from the health care provider. In addition, this section examines several factors that affect older persons’ willingness to participate in research and offers some lessons learned to help in recruitment of elderly patients into studies.

Measuring Driving Performance

This document concludes with a section that reviews the literature on methods to measure driving performance. This includes discussing the pros and cons of on-road testing and driving simulation to measures driving performance. The advantages and disadvantages of naturalistic studies (driving in traffic) and controlled driving (driving on a closed course) are presented along with reviews of the different levels of driving simulation measures that range from noninteractive, computer graphic, or digital video visuals with no motion, to interactive, computer graphic visuals with full motion. This section highlights methods that appear to hold the greatest promise for evaluating the effects of drugs on driving performance while also acknowledging shortcomings and limitations that have been reported in the literature.

A bibliography containing over 200 citations is included, plus an appendix identifying potentially inappropriate medications commonly prescribed for older, community-dwelling individuals.

How To Order

For a copy of Literature Review of Polypharmacy and Older Drivers: Identifying Strategies to Collect Drug Usage and Driving Functioning Among Older Drivers, prepared by TransAnalytics, LLC, write to the Office of Research and Technology, NHTSA, NTI-130, 400 Seventh Street SW., Washington, DC 20590, fax 202-366-7096 or download from www.nhtsa.dot.gov.  Suzanne Feldman, Ph.D., and John Siegler, Ph.D., were the contract managers.

One notable finding that provides perspective on the issue of polypharmacy and older adults was a cohort study of nearly 28,000 Medicare+Choice enrollees cared for by a multispecialty practice (an ambulatory clinic setting) during a 12-month study period between 1999 and 2000. Researchers found that 75 percent of the sample received prescriptions for 6 or more prescription drugs (Gurwitz, Field, Harrold, Rothchild, Debellis, Seger, Cadoret, Fish, Garber, Kelleher, and Bates, 2003).  Residents of long-term care facilities were excluded from the study.  The average age of the subjects in the sample was 74.7 (sd=6.7). The age and gender distribution of the sample were similar to that of the U.S. population who are 65 and older.  Forty-nine percent of the sample was prescribed medications in 4 or more categories.  Combinations of medication use were not reported; however, the specific prescription medication categories and percentage of enrollees receiving prescriptions were as follows:

TRAFFIC TECH is a publication to disseminate information about traffic safety programs, including evaluations, innovative programs, and new publications. Feel free to copy it as you wish. If you would like to receive a copy, contact Patricia Ellison Potter, Ph.D., Editor, fax 202-366-7096, e-mail: patricia.Ellison-potter@nhtsa.dot.gov.