Traffic dangerous drugs are often found in fatally injured older male drivers.

Abstract

To the Editor: Many pharmaceuticals impair driving ability. The impact of drugs on driving ability in older drivers has been discussed previously,1–5 and an increased crash risk has been found for use of cyclic antidepressants6, 7 analgesics,7 and anxiolytics.6 In Scandinavia, most (but not all) drugs influencing driving capacity are identified specifically by a red warning triangle on the cover,8, 9 and the prescribing physician must inform the patient about adverse effects of drugs on driving capacity. Furthermore, written information about the red triangle as a warning for a “traffic dangerous drug” is given along with the drug at the pharmacy. We investigated blood levels of traffic dangerous drugs (TrDD) in all fatally injured older drivers (65 +) referred for forensic toxicology during 1991 to 1995. Of the 345 older drivers killed in Sweden, 86% were autopsied, and 194 cases were referred for toxicology (65%, mean age = 75.4, 86% males). Those who survive the crash and subsequently die in the hospital are not normally referred for toxicology. TrDD included drugs marked specifically on the cover,8, 9 tricyclic antidepressants,6 and neuroleptics with sedating effects.1 All these drugs can be detected and quantified by the National Forensic Chemistry Laboratory. The limits for therapeutic and toxic levels are described elsewhere.10 Drugs given during resuscitation are not reported here. We found TrDD (Table 1) in 27/194 cases (one female (4%), 26 males (16%)). Two or more TrDD could be detected in five of the males. In males aged 65 to 74 years, TrDD was detected in 6.6% (5/76) compared with 23.3% (21/90) in male drivers more than 75 years of age (x2 = 8.76, df = 1, P = .003). In 27% (7/26) of males found with TrDD, the concentration of the drug in the blood was above the upper limit of the therapeutic interval, and in four of these, toxic levels were measured. Knowledge about older drivers and drugs that influence driving is very limited. The proportion of older drivers has often been small and, therefore, not reported separately11, 12. In the study by Leveille et al.,7 an increased crash risk for users of opioid analgesics was found, and this group of analgesics was also the most common TrDD found in our study. Experimental studies with older drivers in simulators or on the road with TrDD have not been reported. The defined daily dose/1000 inhabitants/day, derived from sales statistics, is a measure of the average number of drug users (ANDU) at a given time. We compared ANDU with our results (adjusted to 1000 and gender) for several drugs (groups). We found dextropropoxyphene 2.1 times more often than expected among drivers aged 75 and older who died compared with sales13 to the same age group. This type of comparison is probably an underestimate as older active drivers are known to use fewer drugs than persons who do not drive.14 We found the same pattern with more drug users among the oldest drivers compared with ANDU for diazepam (3.9 times), and hydroxizin (8 times). Interestingly, we found fewer hypnotics than expected according to sales statistics, probably because of the short half-life (t 1/2) of modern hypnotics and because most crashes occurred after noon. This might also explain why we found more nitrazepam than flunitrazepam, contrary to sales statistics. Obviously, warnings about adverse drug effects are sometimes not heeded by the user. Increased risk for fatal crashes among older drivers using drugs can be explained in several ways. Firstly, aging leads to physiological changes that may result in increased levels as well as prolonged duration of action of many compounds. Second, older people are often more sensitive to drug actions,15, 16 particularly effects on the cardiovascular system and the central nervous system. Third, concurrent use of several drugs increases the likelihood of adverse drug reactions as well as the risk of drug interactions. The fundamental issue of whether it is the disease or its pharmaceutical treatment that increases the risk of fatal crashes can perhaps never be properly resolved. No study has so far investigated the blood levels of pharmaceuticals in older drivers on the road. Such data could give a crash risk figure for the disease in combination with drug treatment. Cross-over- designed performance studies with healthy and ill drivers in simulators or on special roads can help judge the degree of driving impairment caused by the drug but not the crash risk per se. In conclusion, it is important to be aware that 75 to 90-year-old patients may also be motorists and to give them appropriate information about the influence on their driving safety of disease and drug treatment. This will be even more important in the future when an increasing proportion of the older population will be drivers.