The fading line between biosimilar and interchangeable

For more than a decade the United States has sorted lower-cost copies of biologic medicines into two tiers. Every biosimilar approved by the US Food and Drug Administration (FDA) must be highly similar to its reference product with no clinically meaningful differences. A smaller group has carried an additional label, interchangeable, and that distinction is now being steadily dismantled by regulators and lawmakers alike.

The practical difference between the two tiers is narrow but real. An interchangeable biosimilar can be dispensed in place of the originator at the pharmacy counter without the prescriber being consulted, much as a generic pill is swapped for a branded one, subject to each state's substitution laws. A plain biosimilar cannot be substituted that way.