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 α and β, 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.