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8 also at significantly higher risk of serious injury in crashes greater restrictions on driving (Vernon et al. 2001). Thus, a (Medical News Today 2007). For a comprehensive review of diagnosis for diabetes alone may have little value in explain- this literature, see Charlton et al. (2004). ing safety outcomes. There is also reason to believe that the medications used to treat diabetes, rather than the medical Conditions That Impair Psychomotor Function condition itself, is of greatest concern. The interested reader is urged to consult more exhaustive summaries such as the Impairments in psychomotor functioning that occur with NHTSA compendium Medical Conditions and Driving: a increasing prevalence among older persons may have a Review of the Literature (Dobbs 2005). neurological origin (e.g., Parkinson's disease) or may be the result of musculoskeletal diseases--especially arthri- tis--that result in weakness, frailty, and/or restricted range Medication Use and Safety Concerns Among of motion. According to a Parkinson's Disease Founda- Older Drivers tion report (2004), the muscle tightness resulting from this disease can slow reactions to hazards and changing traf- Medications that have known effects on the central nervous fic patterns. However, it is the side effects of medications system (CNS), blood sugar levels, blood pressure, vision, commonly used to treat Parkinson's that may be of greatest or other functions have the potential to interfere with driv- concern. These medications often produce sleepiness, dizzi- ing skills and as such have been termed "potentially driver- ness, blurred vision, and confusion, and one class (anticho- impairing" (PDI) medications (LeRoy and Morse 2008). PDI linergics) can be especially dangerous, producing confusion effects include sedation, low blood sugar levels (hypoglyce- and sedation along with memory impairment. mia), blurred vision, low blood pressure (hypotension), diz- ziness, fainting (syncope), and loss of coordination (ataxia). The prevalence of arthritis among individuals in the Often, patients who take over-the-counter or prescription United States is pronounced, with more than 40 million (pri- medications are not aware of the potential impact that these marily older) people affected, 7 million of whom report lim- medications can have on their ability to drive a vehicle safely. ited activity as a result of the disease (Arthritis Foundation Adverse drug events leading to hospitalization are more com- 2007). The most common form is osteoarthritis, a degenera- mon among older adults, reflecting their increased use of sin- tive joint disease characterized by the destruction of carti- gle and multiple medications (polypharmacy) as well as age lage resulting in bone-on-bone friction, pain, deformities, differences in the way they metabolize medication. and restrictions in mobility. Clinicians may diagnose arthri- tis through physical examination; a diagnosis of osteoarthri- In 1998, older persons made up approximately 12% of tis is confirmed through X-ray imaging. the U.S. population, but they consumed 32% of all prescrip- tion drugs (Rathmore et al. 1998). Using prescription claims A diagnosis of arthritis, plus the use of nonsteroidal anti- data, Thomas et al. (2001) found that the average number inflammatory drugs (NSAIDs), was significantly associated of therapeutic classes for which older persons receive drugs with at-fault crash risk by McGwin et al. (2000). However, is 4.66, compared with 2.99 for persons under age 65. Spe- according to Henriskkson (2008), patients driving cars that cifically, the claims data for older persons revealed that 90% have been adapted for their musculoskeletal restrictions are not used cardiovascular medications, and among these patients at increased risk of a crash. As discussed in another section, more than 50% also took a gastrointestinal medication, 50% two areas of functional loss related to musculoskeletal disease took a lipid-lowering medication, and almost half took anti- that significantly predict the risk of an (at-fault) crash among depressants or anti-arthritis medications. older drivers are head-neck mobility and lower limb strength and flexibility [Staplin et al. 2003(a); Ball et al. 2006]. Consistent findings emerged from a cohort study of nearly 28,000 Medicare+Choice enrollees, which found that 75% of The potential scope of a review of material on this topic the sample received prescriptions for six or more medications is enormous. Certain rare conditions that may result in loss (Gurwitz et al. 2003) and 49% of the sample was prescribed of consciousness, such as epilepsy and syncope, have been medications in four or more therapeutic categories. A national excluded from this discussion. The effects of alcohol on driv- survey by Gurwitz (2004) found that among noninstitution- ing also have been excluded. Another omitted disease that is alized adults age 65 and older in the United States, 90% use becoming increasingly prevalent among older persons, dia- at least one prescription medication each week, 40% use five betes mellitus, deserves special attention. Although some or more, and 12% regularly use 10 or more. studies have suggested that diabetics experience an elevated crash risk, a Utah-based Crash Outcome Data Evaluation The risks of polypharmacy include an increase not only System (CODES) analysis including more than 10,000 in the number of potentially inappropriate prescriptions, but drivers with diabetes mellitus and no other known medical also in cognitive disorders, depression, and an increased risk condition showed that the effect size was modest, and disap- of motor vehicle crashes, as discussed later. As LeRoy and peared among drivers with higher levels of impairment and Morse (2008) reported, the following factors account for
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9 the increase in the number of potential drug interactions in sharply for those ages 50 and older versus the ages 1649 older adults: group, continued to climb as the database was truncated at successively older 5-year cohorts, then leveled off when the · An increase in the number of drugs taken daily. age-65-and-older threshold was reached. These findings are · Alterations in pharmacokinetics (the process by which summarized in Table 1 for all crash-involved drivers: a drug is absorbed, distributed, metabolized, and elim- inated by the body). · Long-term drug use. TABLE 1 · Alteration in gut surface area. Mean number of PDI medications at time of crash, · Decrease in gastric motility. by driver age · Decreased gastric acid secretion. Driver age group · Multiple drugs competing for binding sites on serum 16-49 50+ 55+ 60+ 65+ 70+ 75+ albumin. Number · Multiple drugs competing for metabolic enzymes. in 18,837 3,737 2,212 1,208 643 474 299 · Increase in the proportion of fat to body mass. database · Decreased body water. Mean · Reduced liver size with diminished ability to metabo- number of lize drugs. PDI 0.42 1.28 1.43 1.56 1.63 1.66 1.64 · Less efficient renal clearance of drugs. medica- tions The side effects of normal doses of drugs that are par- ticularly relevant to older adult drivers include dizziness, As indicated in the following figures, the rate of use of drowsiness, tremors, rigidity, confusion, hypoglycemia, multiple PDI medications by crash-involved drivers climbs hypotension, and blurred vision. with age until leveling off at the ages 6569 cohort. Another perspective on these data is provided by the following graph- Data describing the crash risk associated with therapeu- ics, which look more narrowly at the contrast between zero, tic classes of prescription drugs are rare, and are not specific one, and multiple drug usage. Figure 1 presents these rela- to commercial vehicle operations. LeRoy and Morse (2008) tionships in a bar graph, whereas Figure 2 focuses more used an administrative pharmaceutical claims database to closely on the changes in multiple drug use with driver age. determine how often various medications and combinations of medications showed up among members who had expe- rienced a motor vehicle crash compared with those who had not experienced a crash. The study evaluated the medica- tion use of 33,519 members with crashes (5,378 of whom were age 50 or older) and of 100,000 controls (three for each case) matched on age and gender without crash involvement. The cases must have sustained an injury severe enough to result in a hospital treatment and an associated insurance payment, and must have had at least 6 months of continuous coverage before the date of the crash/injury. Information in this patient-level database allowed a determination of which medications were current at the date of the crash. FIGURE 1 Proportion of crash-involved drivers within each In the LeRoy and Morse (2008) analysis, drivers were 1.2 age cohort taking none, versus one, versus multiple (two or to 7.5 times more likely to have been crash involved if they more) PDI medications at time of crash. had taken medications in 35 of 90 PDI medication classes. Of the 35 pharmacologic classes highlighted in their research, These graphs suggest that the number/proportion of 27 have specific warnings about sedation, dizziness, drowsi- crash-involved drivers taking multiple (two or more) medi- ness, and the need for caution when driving, especially until cations increases significantly with increasing age. A chi- the effects of the medication are known. square analysis confirmed that the observed values for "0," "1," and "2 or more" medications by different age groups, A subsequent data mining project looked specifically at as shown in Figure 1, significantly exceed the expected val- the relationship between driver age, PDI drug use, and crash ues ( p < 0.001). This test result may be explained by the involvement (Staplin et al. 2008). This study revealed that lower-than-expected use of PDI medications by the ages the (mean) number of "current" (at time of crash) PDI medi- 1649 groups and the higher-than-expected use by the cations taken by drivers in different age groups increased older driver cohorts.