Vertex Pharma Swaps Endpoints in Key Cystic Fibrosis Studies

Vertex Pharmaceuticals ( VRTX) swapped around the primary and secondary endpoints of the two phase III clinical trials dubbed "Traffic" and "Transport" which are investigating combination therapy in cystic fibrosis patients.

The primary endpoint of both cystic fibrosis studies is now the absolute change in lung function, which before Thursday was a key secondary endpoint. Relative change in lung function was the primary endpoint but is now a key secondary endpoint.

The decision to swap out endpoints was made as "part of ongoing discussions with the FDA and was not based on anything going on in the study or anything observed in the study," said Vertex spokesman Zach Barber.

Barber added: "We consider this more procedural because we were always planning to measure and report both absolute and relative change endpoints. Nothing changes in terms of the powering of the study."

The "Traffic" and "Transport" studies investigate the combination of Kalydeco and VX-809 in cystic fibrosis patients with the F508del homozygous mutation. Results from these two studies are expected in mid-2014 and have the potential to deliver $6 billion or so in new sales to the company. To call these studies important for the future of Vertex's cystic fibrosis franchise is an understatement, and naturally, investors are paying very close attention to them.

Absolute change in lung function was the primary endpoint of the phase III studies which Vertex used to get Kalydeco approved for cystic fibrosis patients with the G551D mutation. With that said, Vertex executives in the past have talked about a 5% relative improvement in lung function as an important efficacy threshold for the Kalydeco-VX-809 combination therapy.

The "Traffic" and "Transport" studies are designed with 90% power to detect a 3% absolute and 5% relative improvement in lung function, measured by forced expiratory volume in 1 second (FEV1).

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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