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BioCryst Trades Sharply Lower Despite Acing Late-Stage Hereditary Angioedema Drug Trial

Shanthi Rexaline

Shares of BioCryst Pharmaceuticals, Inc. (NASDAQ: BCRX), a small-cap biotech that develops small molecules for rare diseases, were trading down by nearly half Tuesday despite a seemingly positive clinical trial readout.

What Happened

BioCryst announced Tuesday that a Phase 3 study dubbed APeX-2, which is evaluating once-daily, oral BCX7353 — a selective inhibitor of plasma kallikrein — in preventing hereditary angioedema, or HAE, attacks, met the primary endpoint for both the 110mg and 150mg dose levels.

The primary efficacy endpoint is the rate of investigator-confirmed angioedema attacks over 24 weeks of study drug administration.

The 110mg dose of BCX7353 reduced the HAE attack rate by 30 percent compared to placebo and the 150mg dose reduced the attack rate by 44 percent.

The company noted that 50 percent of patients receiving the higher dosage saw a more than 70-percent reduction in their HAE attack rate.

Of the 108 patients who completed 24 weeks of study, 100 percent continued into the ongoing 48-week extension phase of the trial, according to BioCryst. 

Both dose levels were found to be generally safe and well-tolerated, with no drug-related serious adverse events reported, the company said.

Notwithstanding the positive results, BioCryst stock is plunging. 

"BCX7353 demonstrates 44% reduction in HAE attack rate, relative to placebo. Statistically significant but clinically disappointing," STAT reporter Adam Feuerstein said in a tweet.

Incidentally, Takeda Pharmaceutical Co Ltd (NYSE: TAK)'s Shire unit has a FDA-approved HAE prevention drug in Takhzyro, which is administered intravenously. The HELP late-stage study on the basis of which FDA approved the drug in August 2018 showed that the drug cut monthly HAE attacks by 87 percent, on average, compared to placebo.

Why It's Important

If approved, BCX7353 will have the distinction of being the first oral treatment option for HAE.

"With successful results from APeX-2, BioCryst is committed to making it easy for HAE patients around the world to access this potentially life-changing oral therapy, and we believe BCX7353 is positioned to become a front-line therapy option," BioCryst CEO Jon Stonehouse said in a statement. 

What's Next

BioCryst said the results of the study support an NDA, with the company planning a submission in the fourth quarter of 2019.

The company expects to file a Marketing Authorization Application in Europe in the first quarter of 2020.

BioCryst said it plans to submit detailed results from the trial for peer-reviewed publication and presentation.

Shares of BioCryst were down 47.56 percent at $3.88 at the time of publication Tuesday. 

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