First Biosimilar Interleukin Approved by the FDA: Amgen Wezlana™ Is Interchangeable with Stelara®

On October 31, the FDA announced that Amgen’s biosimilar ustekinumab has won approval as an interchangeable product, marking the first biosimilar approval in this drug category and the first biosimilar for any interleukin agent.

Dubbed Wezlana (ustekinumab-auub), the biosimilar is approved for all of Stelara’s indications, including: moderate-to-severe plaque psoriasis (adults and children ≥ 6 yr), psoriatic arthritis (adults and children ≥ 6 yr), moderate-to-severe Crohn’s disease (adults), and moderate-to-severe ulcerative colitis (adults). Wezlana and Stelara labeling will reflect similar warnings and adverse events profiles. Amgen completed a multiswitching interchangeability study in February 2023.

Stelara, an interleukin 12/23 inhibitor, was first approved in 2009, and its principal patent expired in September of this year. However, due to settlements reported previously, the product will likely launch on January 1, 2025. Competition for this drug class in 2025 may mirror many of the adalimumab market dynamics that we experienced this year. Ustekinumab is another drug that is covered primarily under the pharmacy benefit (or Part D).

Johnson & Johnson reported $6.5 billion in 2023 US revenues for Stelara, an 8% increase over 2021. That represents an extremely attractive target for prospective biosimilar manufacturers: Currently, six companies have either completed phase 3 trials or filed their 351(k) applications with the FDA.

One complicating factor, however, is Medicare price negotiations. Stelara was specifically named as one of the initial 10 pharmaceuticals targeted for price negotiation. The effect this could have on an ustekinumab maker’s revenues just after the start of biosimilar competition (Medicare negotiated prices take effect on January 1, 2026) are very much an unknown. For example, if adalimumab-like competition occurs in the ustekinumab category, the discounts offered by biosimilar manufacturers may far exceed those negotiated by the Centers for Medicare and Medicaid Services in September 2024, under the terms of the Inflation Reduction Act. Negotiation may yet be avoided altogether under the Biosimilar Special Rule provision.

Several other monoclonal antibodies that target other or more specific interleukin receptor subtypes (e.g., 17A, 23) will eventually be candidates for biosimilar competition.

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