The Bothell-based biotech’s stock rose as much as 62 percent, its biggest intraday gain ever, after saying that its experimental infusion to prevent migraines met the main goals of a midstage trial.

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Alder Biopharmaceuticals rose as much as 62 percent, its biggest intraday gain ever, after saying its experimental infusion to prevent migraines met the main goals of a midstage trial.

Alder’s drug ALD403 knocked down migraine days by at least 75 percent per month in 41 percent of patients on its highest dose, according to a company statement Monday. The Bothell company, which sold shares in an initial public offering in May 2014, closed up $8.52, or 49.6 percent, at $25.70 Monday.

The results help Alder keep pace in a tight race with drugmakers Teva Pharmaceutical Industries, Amgen, Eli Lilly and Allergan, which want to get migraines therapies to market that use the same approach as Alder’s, called anti-CGRPs. These work by suppressing the CGRP protein, which is believed to have an important role in maintaining pain and causing migraines.

On a call with analysts, Alder Chief Executive Randall Schatzman said he expects the competitor drugs to enter the market within nine to 12 months of each other. 

Schatzman said 13 million patients nationwide are candidates for migraine prevention, including 3 million with chronic migraine, meaning they experience 15 or more headache days per month, with eight or more classified as migraine days.

“This morning’s data provide clear confirmation of ALD403’s effectiveness in migraine prophylaxis and clean safety profile,” Brian Abrahams, an analyst at Jefferies who recommends buying the shares, wrote in a note to clients. “We see this as addressing key uncertainties and setting the stage for share appreciation to levels more reflective of 403’s late stage of development and multibillion-dollar market potential.”

In the 12 weeks after one infusion of ALD403 at both the highest and second-highest doses, more patients saw their chronic-migraine days decline significantly than those infused with a placebo. About 23 percent of 116 patients on placebo saw their migraine days fall at least 75 percent per month, compared with 39 percent of the 232 on the two highest doses of the Alder drug.

Schatzman told analysts said the safety data wasn’t available, but that nothing had been seen yet that differed from previous trials.