Pfizer looks set to add a lucrative new indication for its fast-growing arthritis treatment Xeljanz after more positive data in psoriasis.

The results of the OPT Pivotal #1 and OPT Pivotal #2 trials showed that the Janus kinase (JAK) inhibitor, given at a dose of 5mg or 10mg twice-daily, was significantly more effective than placebo in clearing psoriasis lesions after 16 weeks' treatment.

Pfizer has not yet revealed details of the new data, but said it now plans to press ahead with a regulatory filing for Xeljanz (tofacitinib) in the US by early 2015, in the hope of adding to its current approved use in moderate-to-severe rheumatoid arthritis.

Last October Pfizer reported data from a phase III trial (OPT Compare) which showed that Xeljanz was as effective as Pfizer's own blockbuster Enbrel (etanercept) when given at a 10mg dose to patients with moderate-to-severe chronic plaque psoriasis, although the 5mg dose did not meet the criteria for non-inferiority.

In another trial - OPT Retreatment - Xeljanz met the primary efficacy endpoints at both doses, showing that a greater proportion of patients continuing Xeljanz treatment maintained their response during the treatment-withdrawal phase compared to patients who switched to placebo.

Xeljanz has got off to a reasonable start for Pfizer since its launch in 2012, adding $114m to the company's coffers in 2013. Its take-up has been held back by the FDA's decision to approve only the 5mg dose - saying the 10mg dose was not considered to have an adequate risk-to-benefit ratio - as well as Pfizer's failure to secure its approval in Europe.

Xeljanz had once been tipped as a $3bn-a-year blockbuster, but the knockbacks in the US and Europe have led analysts to scale down their expectations to around $1bn, at least in the near-term.

As an oral therapy Xeljanz could gain some upside from approval in moderate-to-severe psoriasis, although it could face stiff competition from entrenched therapies such as Enbrel, AbbVie's Humira (adalimumab) and Johnson & Johnson's Remicade (infliximab).

"Psoriasis is a long-term disease with no cure that can have a significant impact on patients," said Steven Romano, global medicines development lead at Pfizer.

Xeljanz has the potential to become "an important new treatment option for adults with moderate-to-severe chronic plaque psoriasis," he added.

