medwireNews: Two follow-up analyses of a randomized trial suggest that the etanercept biosimilar SB4 and its reference product have similar long-term efficacy and safety profiles in patients with rheumatoid arthritis (RA), and switching to the biosimilar is not associated with adverse events or loss of response.
Previous results from the phase III study demonstrated equivalence of SB4 and etanercept at 24 weeks among patients with moderate-to-severe disease despite methotrexate treatment, say Paul Emery (University of Leeds, UK) and fellow researchers.
The 1-year follow-up results, published in Rheumatology, demonstrate “comparable long-term efficacy” between the two drugs. Emery and team found that the proportion of patients achieving at least a 20% improvement in ACR criteria (ACR20) at 52 weeks was similar between the 224 participants randomly assigned to receive SB4 50 mg/week and the 216 receiving the same dose of etanercept, at 80.8% and 81.5%, respectively.
The 95% confidence intervals of the adjusted difference in ACR response rates, at –8.03% to 6.56%, were within the prespecified equivalence margin, meaning that “therapeutic equivalence between SB4 and [etanercept] was demonstrated,” explain the authors.
Participants receiving SB4 also experienced a similar increase from baseline in modified Sharp/van der Heijde scores as those in the etanercept group, at 0.45 versus 0.74 points.
A total of 58.5% of patients in the SB4 group and 60.3% of those in the etanercept group experienced treatment-emergent adverse events (TEAEs) over the 52-week study period, and a corresponding 29.4% and 36.7% of TEAEs were considered to be related to the study drug. The most commonly reported TEAE was upper respiratory tract infection in the SB4 group, and injection site erythema in the etanercept group.
Taken together, the 52-week safety findings suggest that “SB4 was well tolerated and had a similar safety profile to that of [etanercept],” conclude the authors.
In the second study, Emery and colleagues report the 100-week follow-up results in the Annals of the Rheumatic Diseases. After 1 year, participants in the biosimilar group continued to receive SB4 for an additional 48 weeks, whereas those in the etanercept group switched to SB4 treatment, they explain.
At 100 weeks, the proportion of patients with an ACR20 response was “sustained and comparable” between the 126 participants who continued to receive SB4 and the 119 who switched from etanercept to SB4, at 77.9% versus 79.1%.
And the safety profile of SB4 in the extension period was “similar to that observed in the pivotal etanercept trials,” with 47.6% of patients receiving SB4 throughout the study and 48.7% of those switching from etanercept to SB4 experiencing TEAEs.
The researchers note that “the extension period was not designed to compare equivalence statistically,” but believe that “it provides valuable data on switching from [etanercept] to SB4 in patients with RA.”
And they conclude: “Postmarketing surveillance and registry studies are ongoing to monitor the efficacy and safety of SB4 in various indications.”
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