Section 13: Drugs

13.1 Antidepressants

13.2 Antihistamines

13.3 Benzodiazepines

Introduction

A number of prescription and over-the-counter medications negatively affect cognitive performance (Bruera, Macmillan, Hanson, et al., 1989; Golombok, Moodley, and Lader, 1988; Larson, Kukull, Buchner, et al., 1987; Salzman, Fisher, Nobel, et al., 1992; Tune and Bylsma, 1991). Relevant to this discussion are the findings that the use of medications, including those suspected of adversely affecting driving performance, increases with age (Ray, Gurwitz, Decker, and Kennedy, 1992). According to these authors, in the United States in 1988, the 65 and over age group comprised 12 percent of the population yet received 29 percent of all prescriptions, with approximately 11 prescriptions per person per year. Alberta seniors, representing 10 percent of the population, use more than 25 percent of all prescriptions and submit an average of 17 prescription claims annually (D.U.E. Quarterly, 1994). Other statistics on drug use in the elderly population reveal that the older individual uses an average of four prescriptions and two over-the-counter medications at any one time (D.U.E. Quarterly, 1994).

Medications commonly used by ambulatory elderly individuals include analgesics (opiods), antihypertensives, tranquillizers, antidepressants, antihistamines, and hypoglycemics (Colsher and Wallace, 1993; Ellinwood and Heatherly, 1985; Seppala, Linnoila, and Matilla, 1979). As noted by Ray, Purushottam, and Shorr (1993), benzodiazepines and cyclic antidepressants can impair the safety of the older driver, with sufficient data to raise concerns for opiods, antihistamines, and sulfonlyureas.

Although many laboratory and experimental driving studies have documented drug-induced impairments on driving performance (see Janke, 1994, and Ray et al., 1993 for full reviews), medication use on its own is not an acceptable criterion for determining individual driving competence. The lack of clearly defined criteria for individual drugs is compounded by the presence of multiple drug regimes (polypharmacy), a common occurrence in this population. Moreover, the overall risk rating of poly pharmacy cannot be determined by simply summing the risks of taking individual drugs (Wallace, 1997), making the task that much more daunting, if not impossible.

In addition to the effects of specific drugs and possible interactions of multiple drugs, consideration must be given to the pharmacokinetics (the absorption, distribution, metabolism, and elimination of drugs), and pharmacodynamics (the actions of drugs on the body) in the elderly population (see Catterson, Preskorn, and Martin, 1997 for a review). Both are likely to be altered in the elderly population because of normal aging, the presence of intercurrent illnesses, and the likely possible of drug-drug interactions. There have been calls for the development of a compendium of age-related medical conditions and drug interventions that could be used to inform physicians about which medical conditions and the severity levels, and which drugs and the dosages sufficiently impair driving abilities to warrant recommendations about driving cessation (Association for the Advancement of Automotive Medicine, 1996). However, the potential number of combinations of medical conditions, severity levels, drugs, dosages, and interactions is truly daunting and may in fact be the ultimate limiter of this approach. An alternative approach would be to evaluate the current status of the person, regardless of the medical condition(s), drug(s), or interactions that maybe the causal agents of driving impairment, an approach that could be accommodated with the development and implementation of an empirically validated competence screen.

A review of the studies examining the effects on specific categories of drugs on driving performance is provided below.

A summary of the current fitness-to-drive guidelines (Drugs) for medical practitioners from Australia (1998) and Canada (2000) is presented in Table 34.

Table 34  Guidelines for Drugs

(Reproduced with permission)