November 10, 1997

Initial and Steady-State Effects of Diphenhydramine and Loratadine on Sedation, Cognition, Mood, and Psychomotor Performance

Author Affiliations

From the Department of Neurology, Georgetown University School of Medicine, Washington, DC (Drs Kay and Starbuck and Ms Morris); Department of Dermatology and Cutaneous Surgery, University of Miami School of Medicine, Miami, Fla (Drs Berman and Sukenik); Phase IV Research Unit, Schering-Plough Corp, Kenilworth, NJ (Ms Mockoviak and Dr Harris); and National Cognitive Recovery Foundation, San Diego, Calif (Dr Reeves).

Arch Intern Med. 1997;157(20):2350-2356. doi:10.1001/archinte.1997.00440410082009

Background:  The classic, first-generation histamine1-receptor antagonists used to treat allergic disorders frequently cause sedation. In contrast, sedation is reduced or absent after administration of recommended doses of second-generation histamine1-receptor antagonists. We measured the initial and steady-state effects of diphenhydramine, a first-generation antihistamine, and lorata-dine, a second-generation antihistamine, by means of a comprehensive battery of psychometric tests that mirror real-world tasks.

Methods:  Healthy volunteers (N=98) were randomly assigned in a double-blind fashion to receive loratadine (n=33), diphenhydramine (n=32), or placebo (n=33). A computerized test battery was administered at baseline, on day 1 after administration of the initial dose, and on days 3 and 5.

Results:  After the initial dose, subjects taking diphenhydramine demonstrated poorer cognitive performance than subjects taking loratadine or placebo on tasks of divided attention, working memory, speed, and vigilance. Subjects taking diphenhydramine also reported greater fatigue and sleepiness and lower levels of motivation, and rated the quality of their performance as lower than subjects taking loratadine or placebo. On day 3, subjects taking diphenhydramine continued to show more fatigue and lower motivation, and rated the quality of their test performance as poorer than subjects taking loratadine or placebo. There were no differences between loratadine and placebo after the initial dose or steady-state (day 5) dosing for any measure of cognitive or psychomotor test performance, mood, or sedation.

Conclusions:  Patients taking diphenhydramine may be at risk of lapses and significant errors that may lead to potential hazards and decreased work productivity.Arch Intern Med. 1997;157:2350-2356