If you find yourself in Vienna this April and are tired of looking at really old buildings, there's an increasingly popular medical conference coming up that biotech investors don't want to miss.

The 54th annual meeting of the European Association for the Study of the Liver (EASL) will have dozens of exciting presentations, but readouts from Alnylam Pharmaceuticals (NASDAQ:ALNY) and Intercept Pharmaceuticals (NASDAQ:ICPT) will probably receive the most attention. Here's why.

Check out the latest earnings call transcripts for Alnylam Pharmaceuticals and Intercept Pharmaceuticals.

Two scientists examining a slide.

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Alnylam Pharmaceuticals: Safety concerns

In early March, Alnylam announced positive top-line results from a phase 3 study with givosiran, a potential new treatment for acute hepatic porphyria (AHP). Givosiran is an injection that interferes with RNA in liver cells before it can produce an enzyme partly responsible for AHP.

Patients with AHP experience painful neurovisceral attacks that range from debilitating to life threatening. Givosiran looks as if it can make a big difference for this group because patients treated with it experienced significantly fewer porphyria attacks -- but signs of drug-induced liver injury could derail the entire program.

Since AHP is a rare life-threatening disease, the FDA will probably give givosiran more leeway than usual, but it might not be enough. During the phase 3 trial, investigators noticed elevated circulating liver enzymes at three times the upper limits of normal among 14.2% of patients taking givosiran compared to 2.2% of the placebo group.

Liver toxicity wasn't the only concern; five givosiran-treated patients experienced chronic kidney disease, which didn't happen at all in the placebo group. While that is troubling, you should know that all five of these patients had documented kidney trouble before they started the trial.

Givosiran is expected to generate peak annual sales of perhaps $600 million by 2030. Alnylam could really use the cash injections, because its first drug launch hasn't taken off yet.

The FDA approved Onpattro for the treatment of a rare inherited disorder in August, and sales reached just $12.5 million. With incoming competition nipping at Alnylam's heels and an R&D budget expected to reach at least $520 million this year, this biotech really can't afford a late-stage failure.

Three scientists discussing a pink test tube.

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Intercept Pharmaceuticals: More convincing this time?

Nonalcoholic steatohepatitis (NASH), or liver inflammation, is a progressive disease damaging the livers of around 20 million Americans with nonalcoholic fatty liver disease (NAFLD). Since NAFLD affects a third of the U.S. population, NASH is expected to become the leading cause of liver transplant by 2020.

Intercept's lead drug, Ocaliva, is already producing significant sales as a treatment for inflammation of the bile duct, a condition called primary biliary cholangitis, that affects a relatively small population. In February, the company announced top-line results from the phase 3 Regenerate study with NASH patients who also had scarring or fibrosis. A 25 mg dosage of Ocaliva significantly reduced fibrosis without worsening inflammation compared to a placebo. Fibrosis improvement is an endpoint the FDA is willing to accept in a new-drug application for NASH, so there's a chance Ocaliva can earn the first approval to treat this huge population.

Unfortunately, Ocaliva didn't significantly reduce inflammation, another endpoint the FDA will accept. The most troublesome figures presented were pruritus, or itchiness, which is more than an annoyance because it could signal liver damage.

The 10 mg dosage of Ocaliva can be dangerous if patients don't build up to it slowly, and 25 mg isn't going to be any easier. Investors should keep an eye open for more safety details from the Regenerate trial when Intercept presents them at EASL.

Luckily for Intercept, Ocaliva sales rose 38% to $178 million last year. Intercept's pipeline isn't nearly as ambitious as Alnylam's, but it's also a lot less expensive. Operating expenses remained flat in 2018 at $465 million. The company's losing money now, but it can probably make ends meet in a few years if Ocaliva earns approval for NASH, or if it doesn't.

Doctor showing a patient their chart.

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Know the risks

Intercept's been able to hold expenses steady, but it doesn't have any other new drug candidates to interest investors. Beyond Ocaliva, the company has one candidate in early clinical-stage development. If Ocaliva's NASH safety profile doesn't improve, Intercept's $3.1 billion market cap could get cut down.

With a $9.6 billion market cap, Alnylam's shares aren't cheap, but they're probably a safer bet than Intercept's. Beyond givosiran and Onpattro, the company has three other potential new drugs in phase 3 studies right now.