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fizer’s oral JAK-3 inhibitor has shown promising efficacy in the treatment of rheumatoid arthritis according to interim results from a Phase II dose ranging study unveiled at the European League Against Rheumatism meeting in Copenhagen.

Presenting the results at EULAR, Dr Roy Fleischmann from the University of Texas in Dallas said: “The development of oral small molecule JAK inhibitors represents a new approach in the treatment of RA. These drugs offer the potential for more precise targeting than existing oral disease-modifying treatments in addition to a more convenient oral administration than biological treatments”.

Twelve-week results from the six-month study showed that a quarter of active RA patients who had failed standard disease-modifying treatments such as methotrexate receiving either 10 mg or 15 mg twice daily of the oral JAK-3 inhibitor CP-690,550 achieved a 70% improvement (American College of Rheumatology ACR 70 score) in their symptoms after 12 weeks of treatment.

The investigational treatment was compared to the anti-TNF adalimumab (Abbott Laboratories’ Humira) or placebo. The percentage of patients achieving ACR 70 scores for adalimumab and placebo at 12 weeks was 3.8% and 5.1%, respectively. CP-690,550 also achieved statistically significantly superior ACR 20 (20% improvement in RA signs and symptoms) and ACR 50 (50% improvement in RA signs and symptoms) at the 5, 10 and 15 mg doses studied. Dr Fleischmann said: “This drug is clearly effective”.

The most frequently reported treatment-emergent, all-cause adverse events with the JAK-3 inhibitor were urinary tract infections, diarrhoea, bronchitis and headache. Michael Berelowitz, senior vice president Clinical Development and Medical Affairs for Pfizer Speciality Care, said: “This compound could represent a promising advance in rheumatoid arthritis treatment for patients who need an alternative to currently available therapies”.

Dr Fleischmann said plans for a Phase III trial using the 5 and 10 mg twice daily doses were underway but no further details were available. He added that if the Phase III trial showed CP-690,550 was as efficacious as anti-TNF agents with a well defined and manageable safety profile, it could be “a major drug for the treatment of rheumatoid arthritis as it is easier to administer and manufacture because it is a small molecule", and “It’s likely to be cheaper than anti-TNF drugs,” he added.

By Rhonda Siddall