Large-cap biopharmaceutical company Vertex Pharmaceuticals (NASDAQ:VRTX) is right in the middle of a product transition from a dual focus on hepatitis C and cystic fibrosis to a full focus on cystic fibrosis – and its first-quarter results demonstrate those struggles.

For the quarter, Vertex reported a 64% decline in revenue, to $118.5 million, despite revenue from cystic fibrosis drug Kalydeco soaring 61%, to $99.5 million. Its huge revenue drop came from Vertex pulling away from marketing its hepatitis C therapy Incivek, which saw product sales fall to just $3.9 million. (Keep in mind this was the previous fastest-growing drug to ever reach $1 billion in sales.) Comparatively, Incivek produced $205.6 million in sales in the first-quarter last year.

The good news here is that focusing solely on cystic fibrosis dropped Vertex's operating expenses to $334.8 million from $766.7 million in the prior-year period, although research and development expenses rose 10%.

Vertex's adjusted bottom-line results reversed course from a $5.7 million profit, or $0.03 per share, in the year-ago period to a huge $151.4 million loss, or $0.65 per share. Vertex blamed the loss on reduced sales of Incivek and lower royalty revenue from Incivo. Vertex also ended the quarter with $1.32 billion in cash.

Looking ahead, Vertex is forecasting full-year revenue of $520 million-$550 million, excluding revenue from Incivek and its Incivo royalties, with Kalydeco revenue of $470 million-$500 million. Operating expenses are anticipated to be in the $890 million-$930 million range.

Subsequent to its earnings release, Vertex also announced that the addition of VX-661 to Kalydeco improves lung function in cystic fibrosis patients who are heterozygous to the F508del and G551D mutations in a phase 2 proof-of-concept study. Treatment involving this combo produced a mean within-group relative improvement in lung function of 7.3%.

Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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