“Abatacept yields moderate effectiveness for treating the arthritis component of PsA, and the safety profile is reasonably good,” Dr. Philip Mease from Swedish Medical Center and University of Washington, Seattle, Washington told Reuters Health in an email.
Based on an earlier phase I study in which abatacept brought clinical improvement in patients with psoriasis vulgaris, Dr. Mease and colleagues investigated the safety and efficacy of 3 different dosing regimens of abatacept compared with placebo in 170 patients with PsA.
The dosing regimens included 3 mg/kg, 10 mg/kg, or 30/10 mg/kg (2 initial doses of 30 mg/kg, followed by 10 mg/kg) on days 1, 15, and 29, then once every 28 days thereafter.
By day 169, ACR20 responses were evident in 42% of the 30/10 mg/kg group (p=0.022), 48% of the 10 mg/kg group (p=0.006), and 33% of the 3 mg/kg group (p=0.121). Nineteen percent of the placebo group achieved ACR20.
Improvements in the ACR20 response appeared as early as day 29 (the first assessment after baseline), leveled off by day 85, and persisted through day 169 (the final assessment).
Results were similar for ACR50 and ACR70.
MRI scores for erosion, osteitis, and synovitis were lower at day 169 for all 3 treatment regimens than for placebo, with the greatest differences shown for the 10 mg/kg treatment.
Only the 3 mg/kg group showed modest improvements in investigator global assessment of psoriasis scores at day 169 compared with placebo.
All abatacept groups had higher proportions of patients achieving minimal clinically important improvements in quality of life scores compared with the placebo group, with the highest proportion seen in the 10 mg/kg group (45%). Improvements were first reported at day 15 and persisted throughout the 60month treatment period
Seven patients (4 in the 30/10 mg/kg group, 1 in the 10 mg/kg group, and 1 in the placebo group) experienced serious adverse events, but only 2 (1 each in the 30/10 mg/kg group and in the 10 mg/kg group) were deemed drug-related.
Seven patients (3 placebo, 4 abatacept) prematurely discontinued treatment because of adverse events.
The analysis was limited due to small population size, the presence of patients previously treated with anti-tumor necrosis factor therapies, and relatively short treatment duration.
Nevertheless, Dr. Mease concluded that using abatacept for treatment of patients with psoriatic arthritis “would be fine. Some efficacy in joints is achievable, and there are some patients for whom off label use may be warranted.”
The researchers add, “Data on the long-term effectiveness and safety of abatacept in PsA will be reported in the future from the ongoing open-label, extension phase.”
Abatacept is approved for treating such chronic inflammatory conditions as rheumatoid arthritis and juvenile idiopathic arthritis, where T cells are involved in the disease pathophysiology. It is unclear whether the sponsor, Bristol-Myers Squibb, will seek approval to market abatacept specifically for psoriatic arthritis.
Five of the 13 authors listed Bristol-Myers Squibb as their affiliation, but otherwise there was no disclosure statement for this online report.
Arthritis Rheum 2 December 2010.