Image source: Relypsa.

What: Shares of Relypsa (RLYP), a small-cap, commercial-stage biopharmaceutical company, rose by more than 10% as of 12:45 p.m. ET after upbeat clinical data was presented at a medical conference over the weekend. 

So what: Relypsa presented data from two studies at the 53rd European Renal Association Congress on Veltassa, the company's Food and Drug Administration-approved treatment for hyperkalemia (high levels of potassium in the blood).

The first presentation was from a phase 1 study examining the change in sodium excretion levels in 32 patients' urine when taking Veltassa for eight days. Overall, patients who used Veltassa showed a dose-related decrease in mean urine sodium levels compared with patients who only used placebo. There were also no serious adverse events reported from the study.

Lance Berman, Relypsa's chief medical officer, had this to say about the results:

Patients with heart failure and chronic kidney disease often have restricted fluid and sodium intake, as these may cause congestive symptoms. We presented new data suggesting Veltassa may bind and remove sodium as well as potassium in the gastrointestinal tract, which may be relevant for these patients.

The second study evaluated Veltassa over a 52-week period in patients with chronic kidney disease and type 2 diabetes who had hyperkalemia. These patients were using at least two renin-angiotensin-aldosterone-system inhibitors and the study showed that Veltassa demonstrated a clinically significant decreases in mean blood potassium throughout the 52-week period.

The good clinical news caused Morgan Stanley to upgrade the company's shares, causing shares to pop today.

Now what: While the clinical data that was presented is certainly encouraging, I'd caution investors from jumping into Relypsa's stock based on this news alone. After all, AstraZeneca plc (AZN 0.08%) is set to receive its go/no-go decision from the FDA later this week on ZS-9, its drug for hyperkalemia, and if it wins approval, it will compete head-to-head with Veltassa. Given that the agency might grant ZS-9 a broader labeling claim than Veltassa currently enjoys, providers and patients may prefer to use ZS-9. If true, Relypsa's fast growth could slow considerably.

To help combat that threat, Relypsa is pushing hard to expand insurance coverage for Veltassa, and it's done a great job thus far. As of its last earnings announcement, more than 80% of all plans in the U.S. covered Veltassa. In addition, Medicare and Medicaid will include Veltassa in their 2016 Formulary Reference File and the company has already signed deals with both Express Scripts and CVS Health, two of the nation's largest pharmacy benefit managers.

Relypsa is also pushing hard to remove Veltassa's restrictive labeling as it plans to submit a supplemental New Drug Application to the FDA later this year. The data presented over the weekend hints that it may be successful. 

Still, the company is going to have its hands full as AstraZeneca paid $2.7 billion to acquire ZS Pharma -- the original developer of ZS-9 -- late last year, so you can bet they will fight tooth and nail to make that investment pay off.

Given that some analysts believe that this market could eventually eclipse more than $1 billion in annual sales, this will be a fight worth watching. But with so much uncertainty, I'm content to keep my investment dollar far away from Relypsa's stock.