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Drug Effects on Driving Performance
- John M. Weiler, MD;
- George Woodworth, PhD; and
- Ginger Watson, PhD
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IN RESPONSE:
We agree with de Waard and Brookhuis that delay (phase) is a meaningful, reliable, and sensitive measure related to coherence; in our study, phase produced results similar to those produced by coherence. Their reference (1) should have been cited. Our figure, unlike theirs, demonstrates different drivers with good, median, and poor coherence; we did not show data on the lead vehicle.
Accident data studies are difficult to interpret. Fatal events are rare, and often we cannot ascertain the confounding role of medications. Other studies referenced by Lee and colleagues are not driving studies and used insensitive end points.
We chose the most commonly used antihistamine, diphenhydramine, at a dose (50 mg) commonly taken as needed, consistent with labeling instructions for treating allergic rhinitis. A Warner-Lambert advertisement in lay magazines cites data with Benadryl, 50 mg three times per day, that support our dose choice (2). These data may be from the unreferenced study that Angello and Druce mention, which suggests that first-generation antihistamines have greater efficacy than second-generation antihistamines.
Angello and Druce misinterpret the significance of our end points. Our results are not surprising or inconsistent. Clearly, alcohol ingestion impairs driving performance. However, studies show that after ingesting alcohol, participants can perform a primary task at the expense of secondary tasks (3). In our study, after participants consumed alcohol they performed the car-following experiment at the expense of lane keeping; after receiving diphenhydramine, however, the participants did not perform any task well.
Angello and Druce question “differences between treatments for the primary end point [0.6% to 4.7 %] … [which] are not considered clinically relevant.” Coherence is nonlinear, and percentage changes in different parts of its range are not equivalent. When coherence is re-expressed as residual standard error, the maximum contrast was 18.4%.
The Daimler-Benz Driving Simulator study (4) used insensitive measures and should not be interpreted as demonstrating lack of driving impairment with diphenhydramine (50 to 70 mg). That study was open-label; provided no power analysis; had no placebo group; had an inadequate sample size; allowed the participants to sleep while they waited to drive; and required responses to nine critical events in 20 minutes, limiting opportunity for fatigue or drowsiness. The report did not discuss why all participants receiving the high dose required assistance in leaving the simulator. The study was never published in a peer-reviewed journal. According to those investigators, “the control group knew they were not under medication and believed they could cope with the driving tasks with a vigorous, slightly hazardous style of driving … subjects in the medication groups knew that they had received a drug with sedative effects” (4).
Our results are consistent with a large body of literature indicating that diphenhydramine causes drowsiness and impairs driving performance (5). Most concerning is the finding that drowsiness was a poor predictor of impairment. Until more data are available, nonsedating antihistamines should generally be preferred over sedating antihistamines in patients who drive.
John M. Weiler, MD
George Woodworth, PhD
Ginger Watson, PhD
University of Iowa; Iowa City, IA 52242
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
