AbbVie weighed up the likelihood of Allergan’s Botox facing biosimilar competition before striking a $63bn deal to buy the company in June. The assessment persuaded AbbVie that experimental copies of Botox in development pose little threat to the blockbuster drug, which made sales of $3.6bn last year as a result of rising demand for it in therapeutic and aesthetic contexts.

Talking about Botox at the time of the Allergan deal in June, Richard Gonzalez, CEO of AbbVie, said, “It’s not very well characterized, and it’s in very low concentrations. And for a variety of technical reasons, I would tell you that it’s highly unlikely that we would see a biosimilar against Botox for a long, long time, if ever​.”

As Botox is based on the deadly botulinum toxin, knowledge of the process for producing the drug is particularly tightly guarded. Earlier this year, Allergan took a rival to court for allegedly developing a rival to Botox using manufacturing secrets stolen by its former employees.

The upshot is AbbVie thinks Botox will remain a blockbuster for years to come, providing it with an ongoing source of revenue as biosimilar competition eats into sales of its key drug, Humira. There are dissenting opinions, though.

Gonzalez’s comments were put to Revance CEO Daniel Browne when his company, which is working on a Botox biosimilar, presented its second-quarter results. Browne took a different position to his counterpart at AbbVie.

Browne said, “This is a challenging, but not impossible opportunity. The bar is high, the complexity is high. But I think we came away from the … meeting with the FDA very pleased that there is a route forward​.”