The effect of Cimetidine on the number of melanomas on 41 grey horses

Abstract

Melanomas are one of the most common skin tumors in horses.1,2 Several therapies for the treatment of melanomatosis exist, including the administration of the H2 receptor antagonist Cimetidine. Cimetidine has been found to slow down growth of the primary tumor and preventing disease progression, by acting as an immunomodulator.3,4 The aim of this study was to try to confirm the positive effects of cimetidine on melanomas in a group of 41 grey horses. The 41 Horses of the 63 horses on the Heilan International Equestrian club with different degrees of melanomatosis were given Cimetidine 2,5 mg/kg/TD for three months. Every 30 days the location, number and size of the melanomas were registered. Differences in number of melanomas after three months were tested using descriptive statistics and the Wilcoxon signed test. In this population of horses 65% had melanomas. After the three months of cimetidine administration a significant growth in number of melanomas was found comparing the first and the last measurement. In this study the positive effects of cimetidine on melanomas cannot be confirmed. In contrast, we found an actual growth in number of melanomas after three months of cimetidine administration.