Abstract
Recent advance in treatment of rheumatoid arthritis (RA) has been derived by biological disease-modifying antirheumatic drugs (bDMARDs) targeting cytokines. A Jak inhibitor tofacitinib, the first drug of targeted synthetic DMARD (tsDMARD), a novel category of DMARD, shows similar efficacy profile, but different safety concerns, compared to bDMARDs. It is, therefore, essential to understand the mode of action of tofacitinib in the context of safety and efficacy. We here document the possible mechanism of tofacitinib in patiens with RA, shedding light upon a characteristic adverse event, herpes zoster.