If you're looking for stocks that can add a little excitement to your portfolio, biotech is a great place to start. Clinical-trial results and other binary events regularly send drugmaker stocks surging higher or lower overnight.

If you're not sure where to start looking, you're not alone. Last year, BioPharma Dive counted a record 72 biotech initial public offerings (IPOs) that raised at least $50 million. They were springing up like dandelions long before COVID-19 came along.

With hundreds of important clinical-trial readouts scheduled for more companies than any one person can keep tabs on, it pays to know which ones are worth the most attention. Here's why you'll want to keep both eyes open for upcoming announcements from Alnylam Pharmaceuticals (ALNY 1.36%), Intercept Pharmaceuticals (ICPT), and Karuna Therapeutics (KRTX)

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Alnylam Pharmaceuticals: Apollo-B

Shares of Alnylam recently slipped around 15% overnight in response to a surprising clinical-trial flop for a drug it isn't even developing. Recently, BridgeBio Pharma told investors that people with heart damage caused by transthyretin amyloidosis (ATTR) who received acoramidis failed to outperform the placebo group on the six-minute walking test.

Alnylam's lead drug at the moment, Onpattro, is already approved to treat ATTR patients with nerve damage, but ATTR-mediated cardiomyopathy (ATTR-CM) affects a much larger patient population. Since its approval in 2018, Onpattro sales have already risen to an annualized $481 million, and an expansion to treat the larger patient population could push that figure past $2 billion in a few short years.

The six-minute walking test is also the primary endpoint of the ongoing Apollo-B study with Onpattro and ATTR-CM patients. Investors probably don't need to worry about a disaster similar to the one BridgeBio Pharma reported. Onpattro employs small strands of RNA that interfere with transthyretin production, while acoramidis merely stabilizes the protein.

We'll find out if Onpattro has a shot at earning approval to treat ATTR-CM soon. Top-line data should be ready shortly after the Apollo-B trial wraps up this June.

Intercept Pharmaceuticals: Regenerate

Intercept Pharmaceuticals' lead drug Ocaliva is generating significant sales as a treatment for a relatively rare liver condition called primary biliary cholangitis (PBC). Soon we should know if it can earn a lot more as a treatment for non-alcoholic steatohepatitis (NASH), a progressive disease that threatens the lives of millions of Americans. 

There aren't any available treatment options for NASH, but successful results from the Regenerate study, expected early this year, could make Ocaliva the first. In June, the FDA refused to approve Ocaliva for the treatment of NASH with fibrosis until the company had more long-term safety data.

This year, in addition to much more safety data, the Regenerate trial will read out results of liver biopsies taken after 18 months of treatment. As a treatment for PBC, sales of Ocaliva reached an annualized $371 million in the third quarter. That's nothing to sneeze at, but becoming the first available treatment for the much larger population of NASH patients could quickly push annual Ocaliva sales up over $2 billion by 2025.

In addition to the Regenerate study, we could soon see results from the Reverse trial, which enrolled less-severe NASH patients. The company was supposed to report Regenerate results before the end of 2021, but missed the deadline due to a third-party staffing issue.

Karuna Therapeutics: Emergent-2

Shares of Karuna Therapeutics shot up in 2021 on the back of surprisingly good data for an experimental schizophrenia drug called KarXT. This is a combination treatment made with a powerful antipsychotic called xanomeline that Eli Lilly shelved years ago because of a tendency to sedate patients or make them vomit.

Karuna Therapeutics' contribution is the addition of trospium, an old drug used to treat overactive bladders. Results from a 182-patient phase 2 trial published last February suggest Karuna's approach works as intended.

Investigators measured significant improvements without the side effects that caused Eli Lilly to shelve xanomeline years ago. Just 2% of trial participants discontinued due to treatment-emergent adverse events, regardless of whether they received a placebo or KarXT.

Neuroscience drugs that produce measurable improvements in phase 2 fail to repeat their success more often than they succeed. Karuna Therapeutics measured an 11.6-point improvement on a symptom-severity scale that tops out at 210 points. That was statistically significant but still slim enough to make this a very unpredictable phase 3 readout investors don't want to miss.