Peficitinib in rheumatoid arthritis: is it safe and effective?

This study investigated the safety and effectiveness of peficitinib (Smyraf) in rheumatoid arthritis (RA). 

They found that peficitinib improved RA symptoms and slowed joint damage. 

Rheumatoid arthritis (RA) is caused by inflammation in the joints. This is very painful and leads to joint damage. Disease-modifying anti-rheumatic drugs (DMARDs). DMARDs can be classified as synthetic (csDMARDs) or biological (bDMARDs). Both types of DMARDs can improve RA symptoms. However, over time the effect of DMARDs can lessen. Some patients may not respond to either csDMARDs or bDMARDs.

New drug targets for RA are under investigation. One of these is Janus kinase (JAK) enzymes. JAKs are involved in inflammatory signaling. Blocking JAKs reduces signaling to immune cells. This prevents immune cells from becoming over-activated and damaging joint tissue. Peficitinib is a new JAK inhibitor. It is unclear if peficitinib is safe and effective in RA. 

This study included 518 patients with RA. Patients were randomly assigned to receive peficitinib 100 mg or 150 mg daily or a placebo treatment. Patients were also treated with methotrexate (MTX). At 12 weeks placebo-treated patients were switched to peficitinib. Treatment lasted up to 52 weeks. Disease activity was measured by the ACR20 score. Achieving ACR20 equals a 20% improvement in symptoms. Joint damage was measured using the mTSS score. 

At week 12, ACR20 response was higher in peficitinib-treated patients (58.6% of 100 mg group and 64.4% of 150 mg group) compared to placebo (21.8%). There was less joint damage at week 28 in the peficitinib groups compared to the placebo.

Side effects were more common in peficitinib-treated patients. Most side effects were mild to moderate in severity. The rates of serious side effects were similar between groups. The number of serious infections was higher with peficitinib treatment. 

The authors concluded that peficitinib improved RA symptoms and slowed joint damage in patients with inadequate response to MTX.

The placebo group was only treated for 12 weeks before switching to peficitinib. Also, the study included Japanese patients. Further studies with more diverse populations are needed. This study was funded by Astellas Pharma, the manufacturer of peficitinib.