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Vertex Cystic Fibrosis Combo Therapy Passes Key Confidence Test

Stocks in this article: VRTX

ORLANDO ( TheStreet) -- Checking in from the 2012 North American Cystic Fibrosis Conference, where Vertex Pharmaceuticals (VRTC) presented more detailed data on the VX-809/Kalydeco combination therapy:

Wall Street came into Thursday's presentation seeking greater confidence that VX-809 and Kalydeco worked synergistically to improve lung function in cystic fibrosis patients with the common F508del mutation; and that 600 mg of VX-809 was the most effective dose to move forward into the phase III study. What investors feared was data previously undisclosed that would cast significant doubt on the future of the VX-809/Kalydeco program.

Mission accomplished, for the most part. The data presented were positive and largely in line with expectations, not perfect but without major red flags.

Vertex shares were essentially unchanged following the presentation, up 37 cents to $57.37.

The waterfall plot (see photo below) for 600 mg VX-809/Kalydeco patients showed a consistent treatment effect favoring the two-drug combination over placebo, with no outliers mucking up the results. Six of the 21 placebo patients showed lung function improvement (as measured by FEV1) between days 28-56 of the study compared to 14 of 20 patients treated with VX-809/Kalydeco.

From the start of the study through day 56, lung function for patients in the 600 mg VX-809/Kalydeco arm improved by 3.4% over baseline while lung function in placebo patients fell by 3.3%. The benefit favoring VX-809/Kalydeco over placebo started soon after combination therapy was initiated at day 28 and was clearly better by day 42.

You can't know for sure, but lung function curves presented Thursday suggest patients treated with 600 mg VX-809/Kalydeco had room for more improvement beyond 56 days. This bodes well for the phase III study, especially if Vertex decides to include a higher 800 mg dose of VX-809.

While the 600 mg VX-809 dose shined, the 200 mg dose (1.9% lung function improvement) outperformed the 400 mg dose (0.6% lung function improvement). Both the 200 mg and 400 mg doses of VX-809 outperformed placebo, but the lack of a dose response may raise concerns.

The data on sweat chloride reduction were also a bit confounding, with the 400 mg VX-809 dose outperforming both the 200 mg and 600 mg doses when the drugs were given as monotherapy for the first 28 days of the study. Sweat chloride reductions for the 600 mg VX-809 dose were greater than the 200 mg dose.

The lack of correlation between sweat chloride and lung function improvement did not concern the study's lead investigator, Dr. Michael Boyle of Johns Hopkins School of Medicine, because sweat chloride is "just a biomarker" that is less clinically relevant than improvements in lung function.

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