MEASURING/MONITORING MEDICATION USAGE
To meet the broad objectives of this research (i.e., to determine the effect of multiple medication use on driving functioning), it will be important to ensure that research subjects are complying with their medication regime. Conclusions cannot be made about the effects of medications on driving behavior if the medication is not taken, or if more or less of the medication is taken than prescribed. If the medication regimen is not followed, the intended therapy for the medical condition is not provided, resulting in confounded research results (e.g., functional impairments arising from the untreated medical condition may result in impaired driving performance, as opposed to functional impairments arising from the medications assumed to have been taken causing the impaired driving performance). As an example, Roe, Anderson, and Spivack (2002) found that the probability of a new user continuing donepezil (for mild to moderate dementia) was .797 at 90 days, and .627 at 180 days.38 Almost 14 percent of patients 65 to 94 who continued therapy for at least 180 days showed gaps in treatment of 6 weeks or more. The significance of discontinuing therapy is a decline in cognitive and global functioning within 6 weeks of withdrawal, to the level of functioning as if the patient never took the drug.
Research indicates that specific patient-related factors affect compliance (e.g., depression). A better understanding of these factors can provide a rationale for screening potential subjects for future NHTSA research in this area.
This section of the report begins with a discussion of methods used to measure compliance, including the pros and cons associated with each method, and provides examples of recent research that has employed each method. Following the discussion of methods of measuring compliance, research describing the factors influencing compliance is reviewed. This section concludes with a discussion of older people’ willingness to participate in research studies to uncover their medication use, and the professionals to whom older people are most likely to divulge their medication use.
38 Although this example may seem extreme when considering the population of community-dwelling older people who are likely to be driving, it is not, based on the fact that in all 51 U.S. licensing jurisdictions, drivers with a diagnosis of mild dementia may continue to drive, until which time they fail a DMV road test or their physician submits an unfavorable report to the DMV.