Acute and subchronic effects of levocetirizine and diphenhydramine on memory functioning, psychomotor performance, and mood

Background: Central nervous system adverse effects, such as sedation, often accompany the use of first-generation antihistamines. These effects might interfere with memory functioning and psychomotor performance. Levocetirizine was recently introduced as a new antihistamine said to be free from sedative effects. Objective: We sought to investigate the effects of levocetirizine (5 mg), diphenhydramine (50 mg), and placebo on memory and psychomotor performance after acute (day 1) and subchronic (day 4) daily administration in 48 healthy volunteers (24 men and 24 women). Methods: This study was a double-blind, placebo-controlled, randomized clinical trial. Treatments were administrated on days 1, 2, 3, and 4, 3 hours before the start of the laboratory test battery (performed on days 1 and 4), comprising a word-learning test, the Sternberg Memory Scanning Test, a tracking test (easy and hard version), and a divided attention test (tracking and memory scanning simultaneously). Statistical analyses were performed separately for days 1 and 4 by using analysis of variance. Results: On day 1, diphenhydramine significantly impaired tracking performance (easy: F1,90 = 25.9, P <.0001; hard: F1,90 = 20.5, P <.0001) and divided attention (tracking: F1.90 = 23.8, P <.0001; memory scanning: F1.90 = 22.0, P <.0001). Results on word-learning tests and Sternberg Memory Scanning Tests were not significantly impaired. On day 4, the effects of diphenhydramine did not reach significance. In contrast, on both days 1 and 4, levocetirizine did not significantly impair laboratory test performance. Conclusion: The results show that memory, attention, and tracking performance are unaffected after acute and subchronic administration of levocetirizine (5 mg), whereas diphenhydramine (50 mg) significantly affected divided attention and tracking after acute administration.