What are the typical conversion rates of original biologics to biosimilars in rheumatoid arthritis, psoriasis, psoriatic arthritis, and inflammatory bowel disease (IBD), specifically for tumor necrosis factor (TNF) alpha inhibitors (e.g. etanercept (Enbrel) and adalimumab (Humira)) and interleukin (IL) antagonists (e.g. ustekinumab (Stelara) and vedolizumab (Entyvio))?

From the Guidelines

Conversion rates from original biologics to biosimilars vary significantly across inflammatory conditions, with the most recent and highest quality study suggesting that for rheumatoid arthritis, TNF inhibitor biosimilar conversion rates typically range from 40-70% 1. For rheumatoid arthritis, TNF inhibitor biosimilar conversion rates typically range from 40-70%, with etanercept biosimilars achieving around 50-60% penetration in established markets, as shown in a study published in the journal Gut 1. Adalimumab biosimilars show conversion rates of approximately 30-60% in rheumatoid arthritis, though these rates continue to increase as more biosimilars enter the market. Some key points to consider include:

• For psoriasis and psoriatic arthritis, conversion rates are generally lower, ranging from 30-50% for etanercept biosimilars and 25-45% for adalimumab biosimilars, likely due to concerns about immunogenicity and efficacy in visible skin conditions.
• Inflammatory bowel disease has the lowest conversion rates, typically 20-40% for adalimumab biosimilars, with gastroenterologists showing more hesitancy due to concerns about extrapolation of indications.
• For IL antagonists, conversion rates are generally lower across all conditions, with ustekinumab biosimilars (not yet widely available) expected to achieve 15-30% conversion initially, while vedolizumab biosimilars are still in development.
• Conversion rates are influenced by factors including physician comfort, patient acceptance, payer policies, and national healthcare systems, with European countries generally showing higher conversion rates than the US.
• Non-medical switching policies, where stable patients are switched for cost reasons, can significantly increase conversion rates when implemented, as noted in a study published in the Journal of Crohn's and Colitis 1. The NOR-SWITCH study, a 52-week, double-blind, non-inferiority, phase IV RCT, demonstrated non-inferiority of switching from the bio-originator to the biosimilar, using a non-inferiority margin of 15%, as compared with continuation of treatment with the bio-originator for the aggregate of subjects with the various diseases enrolled 1. However, it is essential to consider the potential nocebo effect, which can impact patient-reported outcomes and treatment discontinuation, as highlighted in a consensus report published in Alimentary Pharmacology and Therapeutics 1. Overall, the decision to switch from an original biologic to a biosimilar should be made on a case-by-case basis, taking into account individual patient factors, disease severity, and treatment history, as recommended by the British Society of Gastroenterology consensus guidelines on the management of inflammatory bowel disease in adults 1.

From the Research

Conversion Rates of Original Biologics to Biosimilars

• The conversion rates of original biologics to biosimilars in rheumatoid arthritis, psoriasis, psoriatic arthritis, and inflammatory bowel disease (IBD) vary depending on the specific drug class or drug 2, 3, 4, 5, 6.
• For tumor necrosis factor (TNF) alpha inhibitors, such as etanercept (Enbrel) and adalimumab (Humira), the conversion rates to biosimilars are significant, with studies showing comparable efficacy and safety between biologics and biosimilars 4, 5.
• A systematic review and network meta-analysis found that switching from biologics to biosimilars of TNF inhibitors for rheumatoid arthritis had comparable effects on primary and co-primary outcomes, including the American College of Rheumatology criteria with 20% response (ACR20) and the Health Assessment Questionnaire-Disability Index (HAQ-DI) 4.
• For interleukin (IL) antagonists, such as ustekinumab (Stelara) and vedolizumab (Entyvio), there is limited data on conversion rates to biosimilars, but studies suggest that biosimilars may be effective and safe alternatives to biologics 3, 6.

Disease-Specific Conversion Rates

• In rheumatoid arthritis, the conversion rate to biosimilars of TNF inhibitors is significant, with studies showing comparable efficacy and safety between biologics and biosimilars 4, 5.
• In psoriasis and psoriatic arthritis, the use of anti-TNFalpha therapy, including biologics and biosimilars, is effective in treating these conditions, but there is limited data on conversion rates to biosimilars 6.
• In inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, the use of biologics and biosimilars, including TNF inhibitors and IL antagonists, is effective in treating these conditions, but there is limited data on conversion rates to biosimilars 3.

Drug-Specific Conversion Rates

• For adalimumab (Humira), a TNF inhibitor, there are several biosimilars available, and studies have shown comparable efficacy and safety between biologics and biosimilars 4, 5.
• For etanercept (Enbrel), a TNF inhibitor, there are several biosimilars available, and studies have shown comparable efficacy and safety between biologics and biosimilars 4.
• For ustekinumab (Stelara), an IL antagonist, there is limited data on conversion rates to biosimilars, but studies suggest that biosimilars may be effective and safe alternatives to biologics 3, 6.