It's been a spectacular year for Cara Therapeutics Inc. (NASDAQ:CARA), Omeros Corporation (NASDAQ:OMER), and Portola Pharmaceuticals Inc. (NASDAQ:PTLA) shareholders. Now that all three of these drugmaker stocks have more than doubled in price this year investors are justifiably concerned they might be at their peak.

Here's a look at reasons investors are cheering for these three biotechs now, and what needs to happen in order for their shares to continue soaring into the long term.

Cara Therapeutics Inc.: On the periphery

Shares of this biotech have soared about 165% so far this year, as good news for its lead candidate keeps rolling in. It's still early, but there are reasons to suspect CR845 could become a powerful tool to fight America's raging opioid epidemic. It dulls pain and itch signals where they originate, in the peripheral nervous system. The candidate's claim to fame, though, is its inability to enter the brain where other opioids trigger euphoria that makes them terribly addictive.

Pills stacked on cash in shape of upward sloping chart.

Image source: Getty Images.

The stock's latest spike occurred after the FDA designated CR845 a breakthrough therapy for the treatment of chronic itching related to kidney failure, which could go a long way to expedite the development and review process.

The unmet need for safe and effective itch relief among kidney disease patients is large enough to expect about $300 million in peak annual sales if the candidate earns approval. Biotech stocks generally trade at multiples several times sales, which suggests Cara's recent market cap of about $804 million could double yet again if CR845 earns approval, and further still if it can tack on additional indications.

Before you get too excited, you should know a 1 mcg per kg dose of CR845 caused some patients' sodium levels to exceed a pre-specified threshold, and nearly derailed the entire program last year. Luckily, a lower 0.5 mcg per kg dosage appears highly effective without sodium spikes. If the sodium issue or another side effect pops up it could be extremely painful.

Omeros Corporation: A real eye opener

Soaring sales of this company's first drug, and encouraging clinical trial results for a candidate in late-stage development, have sent its shares rocketing upwards this year. Since the beginning of 2017, this biotech stock has soared about 150% higher.

Cash stacked in the shape of an upward sloping stock chart.

Image source: Getty Images.

The first act of Omeros Corporation's growth story centers on Omidria, a pupil dilator that helps eye surgeons operate on lenses with fewer complications. Sales of the drug soared 208% last year to $41.6 million and could rise much further. Cataract removals and lens replacements are performed millions of times each year in the U.S. alone, giving this drug $1 billion per year sales potential.

The second act of this biotech's growth story is shaping up to be even more exciting than the first. Its lead clinical-stage candidate OMS721 has been shown to significantly benefit patients with two rare, blood-based autoimmune diseases. If results seen in small mid-stage clinical trials can be repeated in late-stage studies currently underway, Omeros could have a second drug with $1 billion-plus annual sales potential on its hands.

Although Omeros Corporation's market cap has more than doubled this year to about $1.09 billion, there's plenty of fuel in the tank. If Omidria and OMS721 continue on their path to blockbuster status, the stock could double yet again over the next few years.

Portola Pharmaceuticals Inc.: Stopping clots

This stock had already doubled this year before a recent FDA approval drove it much higher. Bevyxxa, formerly betrixaban, recently became the first oral anticoagulant for long-term prevention of lethal embolisms among patients that don't get to move around enough, which pushed its year-to-date gain up to 163%.

Although similar drugs are already generating billions of dollars in annual sales, Bevyxxa has its prophylactic niche all to itself, which could drive its sales into blockbuster territory. With a recent market cap of about $3.37 billion, a successful launch would justify the stock's valuation.

Like Omeros, Portola has another exciting candidate in development. Andexxa has already been shown to safely and effectively neutralize the effects of blood thinners like Bevyxxa, but the FDA refused to approve its application last year due to manufacturing site issues. Although drugs like Bevyxxa prevent dangerous clots from forming, they can also lead to uncontrolled bleeding. Andexxa would be the first drug able to stop these life-threatening events in their tracks.

The company expects to resubmit Andexxa's application in July. If the manufacturing issues have been addressed, a widely expected approval could cause this stock to double once again.

Cory Renauer has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.