Pfizer has reported mixed data from a late-stage trial pitting the efficacy of its JAK inhibitor Xeljanz against AbbVie's super blockbuster Humira, the world's top-selling drug, in patients with rheumatoid arthritis.

Top-line results from the 12-month, Phase III/IV ORAL Strategy trial show that the combination of Xeljanz (tofacitinib citrate) 5mg plus methotrexate (MTX) met its primary target in demonstrating non-inferiority versus anti-TNF therapy Humira (adalimumab) plus MTX.

However, Xeljanz drug failed to hit the mark as a monotherapy when put up against a combination of Humira/MTX or Xeljanz/MTX, potentially dulling its competitive edge in a market soon to be doused with anti-TNF biosimilars cheaper than their reference products.

On the plus side, safety findings were consistent with the known adverse events profile for Xeljanx, Pfizer noted.

"We are pleased that we demonstrated non-inferiority of Xeljanz plus MTX versus Humira plus MTX, reinforcing the efficacy of Xeljanz combination therapy," said Michael Corbo, chief development officer, Inflammation & Immunology, Global Product Development. "We will continue to analyse the monotherapy data from this study and look forward to sharing the full results of ORAL Strategy at an upcoming scientific forum."

Xeljanz was first approved in the US for RA back in 2012 and is still under review in Europe. Back in 2013, the European Medicine Agency's Committee for Medicinal Products for Human Use did not recommend the drug's approval for RA, on grounds that it "did not believe that a consistent reduction in disease activity and structural damage to joints had been sufficiently demonstrated".