Pfizer is celebrating after regulators in the USA gave the green light to Xeljanz, the first Janus kinase (JAK) inhibitor to be approved for rheumatoid arthritis.

The US Food and Drug Administration has approved Xeljanz (tofacitinib) 5mg twice-daily for the treatment of adults with moderately to severely active RA who have had an inadequate response or intolerance to methotrexate. The JAK inhibitor may be used as monotherapy or in combination with MTX or other non-biologic disease-modifying antirheumatic drugs (DMARDs).

As well as being the first JAK inhibitor, Xeljanz will be the first new oral DMARD for RA in more than 10 years. It is approved as a second-line medicine, which means that treatment with a biologic is not required before taking the drug.

The thumbs-up comes with a risk evaluation and mitigation strategy and Pfizer has agreed to conduct post-marketing trials to evaulate long-term safety data and to assess Xeljanz in children with polyarticular juvenile ideopathic arthritis. It was also noted that the drug should not be used in combination with biologic DMARDs or potent immunosuppressives, such as azathioprine and cyclosporine.

Chief executive Ian Read said that Xeljanz is "an important new option that could potentially change the way rheumatologists treat this serious autoimmune disease". Observers believe that the drug is destined to be a blockbuster helped by the fact that it is an oral treatment.

The biologics that have come on the market over the past ten years for RA therapy - Abbott's Humira (adalimumab), Amgen's Enbrel (etanercept) and Johnson & Johnson's Remicade (infliximab) - are injectables. Also, coastwise, Pfizer says that Xeljanz will cost less than these three well-established treatments.