Evaluation of Cimetidine as a Therapy for Dermal Melanomatosis in Grey Horse

This paper describes a clinically controlled study on the effectiveness of cimetidine an H2 receptor antagonist for the treatment of melanoma in grey horses. Fifteen grey horses (age range 18 to 27 years) with dermal melanomatosis were divided in three groups. Group A served as the control group; groups B and C received cimetidine at two different protocols for 60 days (3.5 mg/kg PO, BID and 7.5 mg/kg PO, SID). The number and size of the masses was monitored before, during and after therapy. No differences were found between groups regarding number and size of melanomas before and after treatments (p >0.05). Only in one horse it was possible to notice a slight size reduction of some of the masses however this may have been due to the anti-inflammatory effect of cimetidine as already demonstrated previously. It was concluded that cimetidine is not effective in treating dermal melanomatosis of grey horses. Differences of effectiveness in other studies could possibly be due to the variants of melanomas treated or to different treatment protocols. Further controlled studies are necessary to evaluate cimetidine effectiveness on different type of melanomas and other neoplasias arising from tissues other than skin. Also the mechanism of action of cimetidine on horse melanoma requires further investigation.