A randomized double blind placebo-controlled clinical trial of Ceterizine in horses affected by seasonal headshaking

Headshaking is a threat to the welfare of affected horses. As seasonal headshaking may be triggered by allergic conditions, this clinical trial investigated whether the second-generation antihistamine cetirizine decreased headshaking. The objective was to assess the clinical effect of cetirizine versus placebo on seasonal headshaking. The hypothesis was that it would reduce headshaking by 50% in 50% of the horses. Thirty client-owned horses with seasonal headshaking were selected on the basis of information from the owner and a general clinical examination. In this crossover randomised double-blind placebo-controlled clinical trial, horses were given cetirizine (0.4mg/kg twice daily PO for 7 days) or placebo (same number of tablets twice daily PO for 7 days) in a randomised order, with a washout period of 1 week in between. A 9-minute lunge protocol was recorded on video at the start and after both treatment weeks, and the number of headshakes in this 9-minute period was scored by two assessors in a blinded manner. Data of 29 horses were analysed. The number of headshakes decreased by more than 50% in 10 horses when they were given cetirizine and in 8 horses when they were given placebo. This difference was not significant (p=0.73). In a mixed linear model incorporating weather conditions no significant treatment effect was found either. In conclusion: no significant effect of cetirizine on seasonal headshaking was found in the group of horses included in this study.