Humira, a monoclonal antibody used to treat multiple autoimmune diseases, was the top-selling drug for years before Pfizer and BioNTech's COVID-19 vaccine achieved unprecedented sales as it helped to bring the pandemic under control in 2021. AbbVie generated Humira sales of $18.6 billion in the U.S. last year. In international markets, sales fell 22% to $2.6 billion in the face of competition from off-patent rivals.

Humira now faces biosimilar competition in the U.S. for the first time. Amgen launched the first Humira biosimilar, branded Amjevita, last month, and nine other copies of the blockbuster biologic could come to market after its six-month exclusivity period ends in July.

"In 2023 all eyes are on adalimumab and its deep slate of incoming biosimilars," Cardinal Health wrote in a report. "We believe the impacts from this [loss of exclusivity] will likely be felt differently depending on the stakeholder group in question, but there is no doubt the evolution of competition in this market will have far-reaching implications for the entire U.S. healthcare industry."

To understand the likely impact of the Humira biosimilars, Cardinal Health surveyed 301 dermatologists, rheumatologists, and gastroenterologists last year. The survey revealed that between 75% and 93% of physicians in each of the specialties are at least somewhat comfortable prescribing a Humira biosimilar. Half of gastroenterologists are very comfortable, and most of the rest are somewhat comfortable.

However, there are caveats to the comfort. Across the three specialties, 62% to 66% of respondents said they will only feel comfortable prescribing adalimumab biosimilars with interchangeability designations. Amgen's Amjevita, like most near-market Humira biosimilars, lacks that critical designation. Boehringer Ingelheim is an exception, having won approval for the first interchangeable Humira biosimilar in 2021.

Interchangeability was one of the top concerns about adalimumab biosimilars cited by respondents to the survey, although in the case of dermatologists and rheumatologists it lagged far behind safety and efficacy as an issue. Many physicians are also concerned about the lack of cost savings to patients and transitioning patients from Humira to a biosimilar.

When deciding whether to switch a patient to a biosimilar, many physicians see certain characteristics as particularly important. Most respondents listed "device/ease of use" and "citrate-free" as attributes that are very important. The Humira biosimilars are largely free from citrate, a buffer that AbbVie removed because it was causing pain, but the excipient is included in some low-concentration formulations.