Lack of Effect of Oral Melatonin on Platelet Parameters in Normal Healthy Dogs

A randomized, prospective, blinded, placebo-controlled study on the effect of oral melatonin on platelet parameters was performed on 40 healthy dogs with normal physical examinations and no clinically significant findings on serum chemistry evaluation. Dogs were randomly assigned to the study group or the placebo-control group and administered oral melatonin or an oral inert tablet, respectively, for 28 days. Dogs in the study group were administered melatonin at 3 mg per os q 12 hr for dogs weighing <15 kg and 6 mg per os q 12 hr for dogs weighing 15 kg or more. Complete blood counts were obtained at 0, 7, 14, and 28 days of medication administration. No adverse effects or sedation were noted in any dog. The placebo group had a statistically significant transient increase in both plateletcrit and mean platelet volume on day 7 relative to baseline, which was not observed in the melatonin group. Oral melatonin did not appear to have a direct thrombopoietic effect in normal healthy dogs. Future studies are required to investigate the pharmacokinetics of melatonin in dogs and the potential benefits of melatonin in both thrombocytopenia and immune-mediated diseases.