The invention is relevant to chemistry of organic compounds, pharmacology and medicine, and is related to prevention and treatment of musculoskeletal diseases in human and animals associated with the disorder of bone and/or cartilage metabolism, particularly with such musculoskeletal diseases as osteoporosis, osteoarthritis and osteochondrosis, using a new salt form of 2, 2-dimethyl-6-((4-((3, 4, 5-trimethoxyphenyl)amino)-1, 3, 5-triazine-2-yl)amino)-2H-pyrido[3, 2-b][1, 4]oxazine-3(4H)-one. A salt of this compound with 4-methylbenzenesulfonic acid including its hydrates, solvates and polymorphic modifications of the salt, hydrates and solvates is featured with acceptable pharmacokinetic parameters and increased efficiency in the inhibition of Src-family kinases and Syk kinase, as well as other therapeutically significant kinases. This invention also covers pharmaceutical compositions containing therapeutically effective amount of the salt according to the invention.