The FDA’s decision last week that an approved generic bupropion wasn’t comparable to GlaxoSmithKline plc’s antidepressant Wellbutrin XL 300 mg (bupropion) raises questions about the hurdles biosimilar developers may face along the new regulatory path.
Those challenges likely would be exacerbated when developing biosimilars to drugs such as antidepressants, which fall into a narrow therapeutic index, according to Pitts. In April 2010, the Pharmaceutical Science and Clinical Pharmacology Advisory Committee voted unanimously, with one abstention, that critical dose drugs constitute a distinct group and that the FDA should develop a formal list of those drugs, he pointed out. In an 11-2 vote, the committee also concluded that existing bioequivalence standards were not sufficient for drugs in the narrow therapeutic index group.
“The issue with biosimilars is interchangeability,” Pitts told BioWorld Today. Differences between small-molecule drugs like Wellbutrin and biosimilars are iteratively more complicated than they are with generics because they involve not just the chemical composition of the product but also the manufacturing process.
“When it comes to biosimilars, you’re talking about molecules that are between 5,000 and 20,000 atoms,” he added. “The question is whether a 5,000-atom biosimilar is less difficult than a 20,000-atom biosimilar. Of course it is.”
Thus, biosimilars developers must prepare to contend with “many, many more ways to cut safety and efficacy” data, Pitts added.
The Budeprion/Wellbutrin decision indicated the FDA now realizes that issues of similarity exist even with small molecules, Pitts said. “With biosimilars, it’s going it’s going to be a billion times more complicated,” he cautioned.
Still, the fact that the FDA is feeling its way along the biosimilars regulatory pathway and potentially revisiting its general approach to extrapolation should give biosimilars developers pause, Pitts suggested.
“Ten years from now, when the FDA has more experience dealing with this, [the pathway] will be more predictable,” he said. “But now, every biosimilar that comes before the FDA for review is going to be a de novo experience. It’s going to be a very difficult, very risky and very problematic process. From a business standpoint, you have to ask yourself: Is this a worthwhile proposition?”
Tough questions with no easy answers.
The complete Bioworld Today article can be found here (bottom right, page one).