Will Genzyme's Fabry pill only steal sales from Fabrazyme? Not if it acts like Cerdelga

Sanofi's ($SNY) Genzyme is testing an oral drug for Fabry disease, which would go up against its own Fabrazyme if and when it hits the market. But don't worry too much about the pill cannibalizing sales. Judging by the recent success of Genzyme's new oral Gaucher treatment, the company thinks it can find a sizable piece of the Fabry pie for its new pill when the time comes.

Cerdelga--Courtesy of Genzyme

Last summer, the company rolled out Cerdelga, which joined its Cerezyme in the ranks of Gaucher treatments. Genzyme priced the newcomer on par with Cerezyme, giving patients a choice between a daily pill or an infusion every two weeks.

The result? Cerdelga "has been very well accepted by the community," Genzyme's head of rare diseases, Richard Peters, told the Boston Business Journal. Since last August, it's moved into third place on the most-prescribed list, trailing market leader Cerezyme and Shire's ($SHPG) Vpriv. And of Cerdelga's patients, less than 40% have switched over from Cerezyme--meaning most of the pill's pool is completely new to Genzyme's lineup.

"What we're hearing from patients is, 'For the first time in my life, I'm free again'," Peters told the BBJ. "It's transformative for these patients."

And that's the kind of success Genzyme hopes to replicate with the Fabry candidate, which is in Phase IIa testing and likely at least a couple years away from an FDA decision. There's just one hitch: Genzyme's Fabry pill may not be the first for the condition by the time it gets the green light.

Enter New Jersey's Amicus Therapeutics ($FOLD), which recently wrapped up late-stage trails for its own oral contender, migalastat. In March, the company said it would be filing an accelerated approval application at the FDA before the end of this year, meaning an approval could come by mid-2016.

The two drugs have different mechanisms of action, though. Fabry patients lack an enzyme needed to break down fats called glycosphingolipids. Where Amicus' drug helps stabilize existing enzymes so they do a better job doing just that, Genzyme's reduces the amount of glycosphingolipids the body produces in the first place. And as Peters pointed out, unlike the Genzyme product, the Amicus med will only work in those with some working enzymes--totaling just 30% to 50% of patients.

"Severe patients may not benefit," he told the BBJ of the rival drug. "I think it's going to be interesting in the community to see how physicians look at the data and absorb this information. It's going to create, I think, an opportunity for an intense scientific dialog around understanding of the disease in different populations."

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