Shares of Vertex Pharmaceuticals (VRTX -11.69%) were sinking 11.9% as of 10:18 a.m. ET on Tuesday. The sharp decline came after the company announced its 2025 first-quarter results on Monday evening.

Vertex reported Q1 revenue of $2.77 billion, up 3% year over year. It posted adjusted earnings of $1.24 billion, or $4.76 per share, up from $1.05 billion, or $4.06 per share, in the prior-year period. However, both top- and bottom-line numbers missed the consensus Wall Street estimates.

In addition, Vertex revealed that it has temporarily paused the multiple ascending dose portion of its phase 1/2 study evaluating experimental messenger RNA (mRNA) therapy VX-522 in treating cystic fibrosis (CF). The company didn't provide any details, stating only that there was a "tolerability issue."

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Putting Vertex's Q1 news into context

Vertex's disappointing Q1 results were primarily due to what the company called "an expected revenue decline in Russia." Sales in the country have been hurt by copycat versions of its CF therapies. However, Vertex believes the issue in Russia "is a limited and isolated matter."

The company is in the early stages of launching two new drugs, CF therapy Alyftrek and non-opioid pain medication Journavx. As sales pick up for these drugs, Vertex should deliver much stronger growth.

What about the clinical pause for VX-522? It's too soon to know what will happen. Importantly, though, Vertex's already-approved therapies treat the vast majority of CF patients. VX-522 targets roughly 5,000 or so patients who can't be helped by the company's CFTR modulators.

Is Vertex stock a buy?

Vertex's share price is still in positive territory year to date despite today's pullback. I think the biotech stock remains an excellent long-term pick because of the growth prospects for Alyftrek and Journavx as well as the tremendous potential for its pipeline programs.