A placebo controlled clinical trial on cetirizine in seasonal headshakers

Trigeminal mediated headshaking is a syndrome that may have several causes and is a potential threat to the wellbeing of the horse. Because one of the possible etiologies is an allergic rhinitis, a randomized double-blinded placebo controlled clinical trial on the effectiveness of cetirizine, an antihistamine, in 30 seasonal headshakers was performed. A lunge protocol of 9 min, consisting of rest, walk and trot, was recorded at the start, after a week of treatment with cetirizine and after a week of placebo. Weather conditions were also recorded and owners kept a diary.The videos were scored for the amount of shakes. The overall amount of shakes was 67 ± 94 at the start and 47 ± 72 on cetirizine. This difference was significant (P = 0.01). Placebo compared to start was not significantly different (P = 0.18) as was cetirizine vs placebo (P = 0.74). Evaluating results of individual horses 10 horses showed >50% improvement on cetirizine and 11 horses showed a >50% improvement on placebo (compared to t = 0). Factors like weather circumstances will be taken into account.This study shows the difficulty of using a clinical trial for a syndrome influenced by weather and many other factors. It does suggest however that even if cetirizine will not be beneficial in all (seasonal) headshaking horses, it may be in some, both diagnostic for proving an allergic etiology, as well as therapeutic which is also suggested by follow-up of these horses and other clinical cases.