OBJECTIVES: Before 2009, etanercept, infliximab and adalimumab were the only tumor necrosis factor alpha (TNF-alpha) inhibitors approved by the US Food and Drug Administration for the treatment of rheumatoid arthritis (RA). Since then, three new therapies have been approved for this indication, including: subcutaneous golimumab in April 2009, certolizumab pegol in May 2009, and intravenous golimumab in July 2013. The objective of this study was to assess how prices of incumbent TNF-alpha inhibitors changed in response to the market entry of new agents.

METHODS: We obtained 2005-2017 monthly wholesale acquisition costs for all TNF-alpha inhibitors approved for RA from Analysource. For each month between January 2005 and January 2017, we calculated the annual cost of treating a standard 80kg/1.80m patient with each drug. We constructed an interrupted time-series analysis with a linear model to test how the entry of new agents affected trends in prices of incumbent products. The linear model regressed the annual cost of treatment against a continuous variable for month, two indicator variables for each period after new drug entry (one for April 2009-July 2013, another for July 2013-end of the study period), and the interactions between each indicator variable and the time variable.

RESULTS: After the entry of subcutaneous golimumab and certolizumab pegol, the annual cost of treatment increased a 284% faster, from US$69 every month between January 2005 and April 2009 to US$196 every month between April 2009 and July 2013 (p-value for trend change<0.001). After the entry of intravenous golimumab, the annual cost of treatment increased by US$488 every month between July 2013 and January 2017 (p-value for trend change<0.001), a 249% faster than during the previous period.

CONCLUSIONS: Although increased competition should theoretically drive prices down, we found that prices of incumbent TNF-alpha inhibitors significantly increased following the entry of new competitors.