An active moiety is the part of a drug that makes it work the way it does and the FDA has regularly interpreted the law to say that drugmakers do not receive 5-year exclusivity unless all ingredients are new active moieties. Currently, the FDA awards only three years of exclusivity if a fixed-dose combination drug contains a previously approved ingredient and if a drugmaker conducted new clinical studies that were essential to approval.
Stribild, a once-a-day pill that was approved last summer, contains four Gilead compounds, only two of which have new active moieties. So unless the FDA grants its request, Gilead (GILD) receives only three years of exclusivity. And the biotech hopes to wring as much revenue as possible from Stribild, which some Wall Street analysts believe can generate up to $1.5 billion in sales by 2016. The treatment costs about $28,500 per patient per year.
Since 1994, however, the agency has denied exclusivity to 10 fixed-dose combination drugs containing both new and previously approved active moieties, according to the Gilead petition. Until now, no drugmaker has challenged the guidelines used by the FDA to make such decisions, but Gilead believes the FDA's historical interpretation "strongly discourages" the development of fixed-dose combinations to the detriment of patients (here is the citizen's petition and related documents).
As a work around, some drugmakers have first sought approval of a new active moiety as a single-ingredient drug to secure five years of exclusivity and then seek FDA approval of a fixed-dose combination including that drug. Gilead argues such strategies are unnecessary, because the FDA interpretation amounts to a rule of thumb that is not binding and, on a broader level, a Gilead spokeswoman says the biotech wants the agency to modify its interpretation of the law in such a way that would encourage further development of fixed-dose combination drugs.
Of course, it is uncertain when the FDA will act on the petition, or whether Gilead will succeed in swaying the agency. But one source familiar with FDA regulations notes that it would be significant if the agency were to change course. Meanwhile, Gilead faces opposition over Stribild pricing from the AIDS Healthcare Foundation, which is angling to place a referendum in front of San Francisco voters to require city officials to hold talks with drugmakers about pricing for ‘essential medicines' (back story).