Hi My Pomeranian Was On Vanectyl For Allergies And It

hi my pomeranian was on Vanectyl for allergies and it helped his arthritist attacks for at least 2 years we changed him for the new medication fe=rom the states apoquel and he started bitting himselg=f and scratching like crazy with full of soars all over his bi=ody ...can i go back on vanectyl for the rest of his life? It's the only thing that helped him for many years he is now 9 years old