Filgotinib is an oral JAK inhibitor that differs from previously characterized tsDMARDs as it is selective for JAK1 over other JAK family members. In this study, filgotinib, which is a selective JAK1 inhibitor is efficacious for psoriatic arthritis treatment in patients with active disease. There were rapid improvements in multiple domains of PsA disease activity, including enthesitis and patient-reported outcomes. 

Involvement of Janus Kinase 1 (JAK1) pathways has already been reported in the pathogenesis of psoriatic arthritis. In this study, efficacy and safety of a selective JAK1 inhibitor, filgotinib for the treatment of psoriatic arthritis has been investigated.

A randomized, double-blinded, placebo-controlled phase 2 trial, by the name of EQUATOR, was conducted on adults from 25 sites in the seven European countries. The subjects were 18 plus years old with active psoriatic arthritis and having a failure to respond to a minimum of one csDMARD (conventional synthetic disease-modifying anti-rheumatic drug). Patients were equally divided into filgonitib 200 mg group and placebo group for 16 weeks. The patients achieving a 20% improvement in ACR20 at week 16 was assigned primary endpoint.

Out of total of 191 patients screened, 131 were randomly divided into filgotinib group (n=65) and placebo group (n=65). 80% of the patients in the filgotinib group achieved ACR20 at week 16 compared to 33% patients achieving ACR20 at week 16 in the placebo group. 57% of patients in the filgotinib group and 59% of patients in placebo faced adverse events. One serous treatment-inducing adverse event which was pneumonia and hip fracture after a fall emerged in each group.

Filgotinib is reportedly highly effective in psoriatic arthritis treatment compared to placebo with least adverse events.