Editor's Note: The original article incorrectly stated that Alynlam was still partnered with Sanofi on patisiran and that most of their pipeline was being developed by partners. This has been corrected. The Fool regrets the errors.

Get ready for a banner year of blockbuster drug launches.

According to a recent report from Clarivate Analytics, 12 new drugs are supposed to hit the market this year and reach $1 billion in annual sales by 2022. While entries from Gilead Sciences (NASDAQ:GILD)Alynlam Pharmaceuticals, Inc. (NASDAQ:ALNY), and GW Pharmaceuticals plc (NASDAQ:GWPH) aren't the largest, these three drugs are so important to the companies launching them that you won't want to stop watching them for a minute this year.

1. Biktarvy: Big losses to offset

AbbVie Inc. (NYSE:ABBV) launched a new hepatitis C virus (HCV) treatment last August, and competitive pricing for Mayvret is hammering sales of everyone else's HCV drugs into the dirt. In the fourth quarter, Gilead's haul from hepatitis C antivirals fell 53% on year, to just $1.5 billion.

Scientist examining a flask.

Image source: Getty Images.

Luckily, Gilead Sciences launched a new HIV tablet in February called Biktarvy that could replace a lot of lost HCV revenue. Unlike hepatitis C, HIV can't be totally cured. Long treatment durations are expected to drive annual sales of Gilead's new single-tablet regimen up past the $5 billion mark by 2022.

For Biktarvy to hit that estimate, it needs to sweep aside Juluca from GlaxoSmithKline (NYSE:GSK). Biktarvy's main competitor is a two-drug combo that the British pharma launched late last year.

The FDA gave Gilead's drug a big advantage over Juluca, which is limited to patients who have already suppressed the virus with another regimen for at least six months. Biktarvy's approved for treatment switchers after just three months of successful viral suppression plus new HIV patients who haven't tried any antiviral treatments yet.

2. Patisiran: First attempt

This drug's expected to generate more than $1 billion in annual sales for Alnylam if it earns widely expected approvals. That isn't nearly as much as Biktarvy, but this could be Alnylam's first marketed drug. After 16 long years as a pre-commercial biotech, patient investors are itching to see some product sales.

The importance of a successful launch for patisiran involves more than just sales. The company sports a robust clinical-stage pipeline.

Patisiran is a potential first in class RNA interference drug that inhibits expression of the transthyretin gene. We all need this protein to cart around thyroid hormones and vitamin A, but in some people, it tends to fragment, fold, and cluster into troublesome plaques. Inhibiting its production with patisiran provided a significant benefit for transthyretin amyloidosis patients during clinical trials, but the drug's success in any commercial setting is far from certain.

Alnylam and Sanofi are waiting for the FDA to complete an ongoing priority review of patisiran's application as a treatment for transthyretin amyloidosis. The agency set Aug. 11 as the target action date, although it has been known to issue decisions ahead of, and behind, schedule.

Close-up of a medicine capsule.

Image source: Getty Images.

3. Epidiolex: A hard sell?

This June, the FDA's supposed to hand down an approval decision regarding this epilepsy drug from GW Pharmaceuticals. If approved, Epidiolex will probably be a hit with epilepsy patients that get to try it, but marketing pure plant-derived cannabidiol (CBD) for an expected $30,000 per year could be an uphill battle. The vast majority of American adults with epilepsy already have easy access to cheap CBD through state medical, and recreational marijuana programs. 

Although Epidiolex might be a tough sell among adults, GW Pharmaceuticals has its patented drug aimed at children afflicted with severe debilitating forms of epilepsy known as Lennox-Gastaut syndrome and Dravet syndrome. Epidiolex significantly reduced seizure frequency for these patients during trials supporting the drug's application, and an approval seems likely.

Unfortunately for GW Pharmaceuticals, there are only around 30,000 patients with Lennox-Gastaut in the U.S., and Dravet is even less common. To achieve blockbuster status, Epidiolex will need to expand beyond the treatment of early onset epilepsy syndromes and into the realm of moderately affected adults.

While I'm not confident about seeing Epidiolex expand into the larger adult population, insurers rarely restrict access to new therapies for rare and deadly childhood diseases. I think modest uptake among this population can drive sales up around $300 million at its peak.

Key takeaway

At recent prices, there's a great deal of success priced into GW Pharmaceuticals and Alnylam. Investors need to understand that even though these companies are on the edge of huge potential windfalls, eye-popping estimates ahead of a new drug's launch disappoint more often than they materialize. If Epidiolex isn't a huge winner, GW Pharmaceuticals doesn't have much in its pipeline to justify a $3.3 billion market cap.

Alnylam has plenty of new drug candidates in late-stage development, but with a recent market cap of $13.9 billion, patisiran plus a few more need to hit the bull's-eye if investors are going to come out ahead over the long run.

There's a lot riding on Biktarvy, but it's already approved, and Gilead knows how to launch an HIV drug as well as any of its peers. Best of all, the company is strongly profitable right now, and the stock offers a nice 3.1% dividend yield that you can keep even if this launch fizzles.

Cory Renauer owns shares of Gilead Sciences. The Motley Fool owns shares of and recommends Alnylam Pharmaceuticals and Gilead Sciences. The Motley Fool has the following options: short May 2018 $85 calls on Gilead Sciences. The Motley Fool has a disclosure policy.