Tofacitinib is part of a new class of drugs called JAK inhibitors, which work by blocking Janus kinase, or JAK, pathways involved in the body’s immune response. Tofacitinib fights inflammation from inside the cell, attacking a different part of the pathway than biologic agents, which block pro-inflammatory cytokines (proteins) – like tumor necrosis factor-alpha and interleukin-6 – from outside the cell.