NEW YORK (AP) — Shares of Anacor Pharmaceuticals Inc. jumped Thursday after the company reported strong data from a clinical trial of a drug intended to treat a type of chronic rash.

Anacor is testing a topical drug called AN2728 as a treatment for atopic dermatitis, a chronic rash that causes inflammation and itching. It most often affects children. The company said patients improved over four weeks of treatment, with most of the gains coming in the first week. It tested two concentrations of AN2728 and plans to move the more concentrated form into late-stage studies.

Anacor Pharmaceuticals shares rose $1, or 26 percent, to close at $4.84. The stock added 36 cents, or 7.4 percent, to $5.20 in after-hours trading.

The trial involved 86 subjects aged 12 to 17. They were treated with one of the two concentrations either one or two times a day for four weeks. Improvement ranged from 54 percent for patients who used a less concentrated version once a day, to 71 percent for patients who used a stronger version twice a day.

The Palo Alto, Calif., company said side effects observed during the study were mild and mostly unrelated to AN2728.