The Collaborative International Dictionary of English v.0.48:

antarthritic \ant`ar*thrit"ic\([a^]nt`[aum]r*thr[i^]t"[i^]k),
antiarthritic
\ant`i*ar*thrit"ic\([a^]nt`[-e]*[aum]r*thr[i^]t"[i^]k), a.
   [Pref. anti- + arthritic.] (Med.)
   Alleviating arthritis. -- n. A remedy for alleviating
   arthritis. --AS
   [1913 Webster]