This year is starting off with a bang for several biotechs. There's a lot going on, from important clinical updates to regulatory decisions. Here's why Amgen (NASDAQ:AMGN), Jazz Pharmaceuticals (NASDAQ:JAZZ), Lexicon Pharmaceuticals (NASDAQ:LXRX), Regeneron Pharmaceuticals (NASDAQ:REGN), and Synergy Pharmaceuticals (NASDAQ:SGYP) are five biotech stocks you'll definitely want to watch in the first quarter.

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Amgen: Two big events

Amgen failed to win approval from the U.S. Food and Drug Administration on its first try with experimental secondary hyperparathyroidism (sHPT) drug Parsabiv. The big biotech thinks it resolved the issues identified by the FDA and resubmitted for approval. A decision is expected by Feb. 9. 

Expectations are high for Parsabiv if it wins approval. Some on Wall Street think the drug could reach peak sales close to those of Amgen's current sHPT drug Sensipar, which generated over $1.4 billion in sales in 2015.

Another huge milestone for Amgen should also come in late first quarter. The company plans to announce results from a late-stage cardiovascular outcomes study for cholesterol drug Repatha. These results could be critical for persuading payers to loosen restrictions on paying for the high-priced PCSK9 inhibitor.

Jazz: No sleep could be a good thing

Jazz Pharmaceuticals expects to announce top-line results from two late-stage studies evaluating JZP-110 in excessive sleepiness in obstructive sleep apnea during the first quarter of 2017. Results from another late-stage study of the experimental drug targeting treatment of excessive sleepiness associated with narcolepsy are anticipated in the second quarter.

If these studies go well, Jazz should submit for U.S. regulatory approval late this year. Goldman Sachs (NYSE: GS) analyst Stephan Stewart thinks JZP-110 could generate peak annual sales topping $300 million if approved. Others have suggested the drug could make as much as $500 million per year.

Lexicon: Waiting a little longer

The FDA originally was scheduled to make an approval decision on Lexicon Pharmaceuticals' experimental oral carcinoid syndrome drug telotristat ethyl by Nov. 30, 2016. However, the agency needed more time. Lexicon now expects the FDA to make its decision by Feb. 28.

Lexicon isn't waiting to be ready to launch telotristat ethyl, though. The biotech is quickly building an infrastructure to support a commercial launch of the drug in the U.S. assuming it gains approval. Telotristat ethyl could potentially reach peak annual sales of more than $500 million.

Regeneron: Needing some good news

Regeneron could use some good news. Earlier this month, a federal judge ruled that the biotech's cholesterol drug Praluent infringed on Amgen's patents for Repatha. Regeneron could potentially receive better news later this quarter: The FDA expects to announce its decision on approval for Dupixent in treating atopic dermatitis by March 29.

While anything can happen in the regulatory process, Dupixent should have a pretty good chance of getting the green light from the FDA. Regeneron should have a big winner on its hands if the drug wins approval for atopic dermatitis and other targeted indications, including asthma. Analysts think Dupixent could hit peak annual sales of up to $3 billion worldwide.

Synergy: Ready for a transformation

Synergy Pharmaceuticals doesn't have a drug on the market yet, but that could change very soon. The FDA is scheduled to make a decision on plecanatide in treating chronic idiopathic constipation (CIC) by Jan. 29.

Gary Jacob, Synergy's CEO, called this decision a "transformative milestone" for the company. He could be right. Synergy reported positive results from two late-stage clinical studies for plecanatide in treating CIC. And there's definitely a big potential market, with around 14% of individuals in North America suffering from CIC. 

Which to watch the closest?

Of these upcoming events, I'll probably watch two the closest. First, Amgen's cardiovascular outcomes study results for Repatha are enormously important for the drug's fate. These results could also shake up the entire cholesterol drug market to some extent.

Second, I'll look out especially for the FDA decision on Dupixent. Regeneron has a lot at stake with this drug. It's even possible that a thumbs-up for Dupixent could ultimately cause Regeneron to become an acquisition target. 

Investors will want to keep their eyes on all of these biotech stocks in the first quarter, though. Potential catalysts are coming.