(Reuters) – Biopharmaceutical company Dyax Corp will halt a mid-stage study of its experimental drug to treat a rare disorder caused due to swelling of the skin, after it failed to show significant improvement compared with a placebo.

The news sent the company’s shares down as much as 16 percent to $1.80 after markets closed on Thursday.

The drug, ecallantide, is Dyax’s lead compound. It is already being sold in the United States since February 2010 under the trade name Kalbitor to treat acute attacks of hereditary angioedema.

Kalbitor garnered net sales of $8 million in the quarter ended March 31, up 14 percent from a year earlier.

Angioedema is a painful swelling of the skin, usually affecting the eyes and lips. It is caused due to allergic reactions or heredity.

The mid-stage study tested the drug as an acute treatment for another particular type of angioedema — one caused due to adverse reaction to a hypertension drug called angiotensin-converting-enzyme inhibitor.

The study intended to enroll 176 patients, but Dyax said interim results from the first 72 patients on ecallantide failed to show a statistically significant trend favoring the drug over placebo.

The placebo showed a much higher-than-expected response rate, and safety was not a factor in deciding to end the clinical trial, the company said.

Dyax last November withdrew a European marketing application seeking approval to sell the drug as a hereditary angioedema treatment, after the agency indicated that the data provided was not sufficient.

The Burlington, Massachusetts-based company plans to present detailed results from this study at an upcoming medical meet.

(Reporting by Zeba Siddiqui and Adithya Venkatesan in Bangalore; Editing by Joyjeet Das)