What's more exciting than watching biotech stocks heading into a major catalyst? Watching three of them in a matter of weeks.

May's going to be a big month for a handful of small-cap biotechs and the Food and Drug Administration. Achaogen Inc. (NASDAQ:AKAO)Akcea Therapeutics Inc. (NASDAQ:AKCA), and Portola Pharmacuticals Inc. (NASDAQ:PTLA) are expecting important approval decisions from the FDA, and success for any of these companies is far from guaranteed.

Here's what you need to know about the flurry of activity ahead.

Scientist using a pipette.

Image source: Getty Images.

1. Achaogen Inc.: Ready for the next step

This clinical-stage antibiotic developer earned a spot on radar screens after its lead candidate, plazomicin, succeeded in a pair of pivotal trials designed to support applications in the U.S. and EU that could make it an important new weapon in the fight against serious infections that resist today's antibiotics. The FDA accepted Achaogen's submission earlier this year but insisted on calling together a panel of independent experts before issuing a decision on its own. 

If approved with an advantageous prescribing label, some analysts think the antibiotic could rack up $500 million in annual sales at its peak. Biotech stocks tend to trade at mid-single-digit multiples of annual revenue. At recent prices, the company sports a $586 million market cap that could surge if the FDA's advisory committee takes a positive view of plazomicin in light of a few potential sticking points.

During the Epic trial, plazomicin showed statistical superiority to a common antibiotic used to treat complicated urinary tract infections on three of four predefined efficacy endpoints. When investigators looked for signs of a clinical cure five days into the study, though, plazomicin merely showed statistical non-inferiority.

In the Care study, researchers tested plazomicin against colistin among patients with infections resistant to carbapenem, an antibiotic typically reserved for serious infections. One group from the study exhibited a 70.5% reduction in all-cause mortality at 28 days. With just 37 patients split into two groups, though, it's no wonder the FDA wants a team of independent experts to weigh in on the submission.

They'll voice, and vote, their opinions on May 2, 2018. The agency doesn't have to follow their advice, but it usually does.

2. Akcea Therapeutics: Volanesorsen AdCom

This pre-commercial stage biotech was spun off from Ionis Pharmaceuticals (NASDAQ:IONS) in 2017 and already sports two drugs under review by the FDA, inotersen and volanesorsen. The company has a date with an advisory panel on May 10 to help the agency come to a decision with volanesorsen's application.

If approved, it would become the first available treatment for familial chylomicronemia syndrome (FCS), an inherited triglyceride disorder that leads to painful pancreatitis attacks for perhaps 4,000 patients worldwide. An approval would also boost confidence in an ongoing study that could expand the drug's patient population to include a second indication.

There isn't a ton of data to work with, but it looks like volanesorsen just about stops pancreatitis attacks from occurring in FCS patients. The application would be a slam dunk if not for some troubling safety signals observed during the Approach study. Ten of 33 patients withdrew from the trial due to side effects, and three of them were hospitalized with low blood platelet counts.

Given the severe unmet need, an approval with harsh warnings seems like the most likely outcome. The FDA could also delay the application indefinitely by asking for more safety data. We won't know the agency's intentions following the meeting, but we'll know which way the wind's blowing.

3. Portola Pharmaceuticals: Second time's the charm?

Volanesorsen will probably remain limited to few thousand patients, but this little biotech could launch a drug that would benefit a huge population of patients taking next-generation blood thinners. Preventing blood clots that can jam up vital organs is important, and drugs that make clot prevention as easy as swallowing a pill are racking up billions in annual sales.

For example, sales of Eliquis from partners Pfizer (NYSE:PFE) and Bristol-Myers Squibb (NYSE:BMY) hit a $6.0 billion annualized run rate after surging 38% in the first quarter. Eliquis is just one of several drugs in its class that would probably become a great deal more popular if there were also an antidote that can quickly shut it down.

The factor Xa inhibitor with the most to gain could be Portola's own. This January, it launched BevyxXa as the first drug in its class approved for long-term prevention of clots.

Preventing clots saves lives, but the occasional bouts of uncontrolled bleeding that factor Xa inhibitors can cause are just as dangerous. Portola's AndexXa showed it quickly reverses the effects of drugs like BevyxXa and Eliquis, but the FDA sent the application back with a request for more information in 2016.

The agency is expected to issue a decision on or before May 4. An approval could send the stock surging, in part because a more recent information request cast a dark cloud over its chances. In short, the agency wants to understand why AndexXa didn't stop bleeds 17% of the time even though it appeared to work according to 90% of patient blood samples taken during clinical trials. 

Look beyond the catalysts

Although it would seem cruel to reject AndexXa's application again, investors need to brace for the possibility that Portola, Akcea, or Achaogen could receive some awful news in the days ahead. With that in mind, it's important to look for a potential safety net.

Achaogen doesn't have anything in late-stage testing beyond plazomicin, so a delay could lead to swift and heavy losses. Akcea's awaiting an approval decision for another rare-disease drug with a larger addressable population than volanesorsen, and Portola's first drug is already on pharmacy shelves. Though good news could send Akcea and Portola booming in May, at least negative news probably won't lead to a total bust.

Cory Renauer has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Ionis Pharmaceuticals. The Motley Fool has a disclosure policy.