The study is an open-label extension of a phase 3 trial that included 68 weeks of treatment with the biosimilar adalimumab, Amjevita, followed by an assessment visit at week 70 and an end-of-study visit at week 72.
Previous research has demonstrated the similarity of Amgen’s ABP 501, Amjevita, to the reference adalimumab, Humira, and supported approval of the biosimilar by the FDA. Last month, researchers published results of an open-label extension study of the phase 3 trial in patients with rheumatoid arthritis (RA) up to 72 weeks.
The study (an extension of a phase 3, randomized, double-blind, active-controlled, 26-week equivalence study in patients with RA receiving methotrexate) is an open-label extension that included 68 weeks of treatment with the biosimilar followed by an assessment visit at week 70 and an end-of-study visit at week 72.
All patients in the study received 40 mg of ABP 501 every other week for the 68 weeks of treatment. In total, 229 patients who had received the biosimilar in the parent study and 237 patients who had received the reference adalimumab in the parent study were included in the extension, and 88.2% completed the study. Patients received a stable dose of methotrexate for the duration of both the parent study and the extension period, and those on a stable dose of oral corticosteroids could continue to take them before initiating adalimumab during the parent study.
Key safety endpoints included treatment-emergent adverse events (AEs), serious AE, and the incidence of antidrug antibodies (ADAs). Efficacy endpoints included the proportion of patients meeting American College of Rheumatology criteria for 20% improvement (ACR20) and change in the Disease Activity Score in a count of 28 joints (DAS28) with C-reactive protein (CRP) from baseline.
Overall, 63.7% of patients who received at least 1 dose of the study drug experienced 1 or more AEs, 9.0% experienced an AE of grade 3 or higher, and 9.9% experienced a serious AE (only 3 patients experienced serious AEs that were considered treatment-related, and most serious AEs occurred in a single patient). The incidence of AEs was similar in the group that transitioned from the reference adalimumab and in the biosimilar-only group.
In total, 48.9% of patients who transitioned to the biosimilar and 54.1% of patients who received the biosimilar only tested positive for binding ADAs at any time; 18.2% of patients developed binding ADAs relative to the baseline of the extension, while 50.2% of patients developed binding ADAs relative to the baseline of the parent study. Furthermore, 6.9% of patients developed neutralizing antibodies relative to baseline in the extension, while 14.2% of patients developed neutralizing ADAs relative to the baseline of the parent study.
In the parent study, at week 24, 74.2% of patients achieved ACR20. In the extension, 77.6% met ACR20 criteria at week 48, and 78.8% met the criteria at week 70. At the baseline of the extension, the mean change in DAS28-CRP from the baseline of the parent study was −2.25. The mean DAS28-CRP change from baseline of the parent study was −2.55 at week 48 and −2.60 at week 70 in the extension. In terms of ACR20 and DAS28-CRP, efficacy was similar among patients in both groups.
“This study provides further evidence of [ABP 501's] efficacy and safety in patients with RA. In this [extension] study, efficacy was maintained, and safety was consistent with the known safety profile for adalimumab, regardless of whether patients remained on ABP 501 or transitioned from the [reference] to ABP 501,” write the authors.
Cohen S, Pablos JL, Pavelka K, et al. An open-label extension study to demonstrate long-term safety and efficacy of ABP 501 in patients with rheumatoid arthritis. Arthritis Res Ther. 2019;21:84. doi: 10.1186/s13075-019-1857-3.