Safety of Masitinib Mesylate in Healthy Cats

Background Masitinib mesylate is a PO-administered tyrosine kinase inhibitor developed both for human and animal diseases with activity against both mutated and wild type forms of the c-kit receptor and platelet-derived growth factor receptors alpha and beta, and is currently registered in Europe for the treatment of mast cell tumors in dogs. Hypothesis/Objectives The objective of this study was to determine if healthy cats can tolerate administration of masitinib without clinically relevant adverse effects. Animals Twenty healthy research colony-specific pathogen-free cats. Methods This study was a prospective, randomized phase 1 clinical trial. Masitinib was administered PO to 20 healthy cats. Ten cats received 50 mg masitinib every other day for 4 weeks, and 10 cats received 50 mg masitinib daily for 4 weeks. Results Clinically relevant proteinuria was noted in 2/20 (10%) cats (both treated daily), and neutropenia was noted in 3/20 (15%) (seen in both treatment groups). An increase in serum creatinine concentration and adverse gastrointestinal effects were noted in some cats. Conclusions and Clinical Importance Masitinib mesylate was tolerated in the majority of cats. Long-term administration and pharmacokinetic studies are needed to further assess the use of masitinib in cats.