Drug developer XenoPort Inc said its experimental drug was effective in treating psoriasis, a chronic inflammatory disease of the skin.

XenoPort's shares jumped 19 percent to $8.00 in premarket trading on Tuesday after the company said the oral drug met the main goal in a mid-stage trial.

XenoPort said it expected to start late-stage trials next year and that it would explore partnerships to speed up the development of the oral drug globally.

Psoriasis, one of the most prevalent yet difficult-to-treat autoimmune diseases, causes itchy or sore patches of thick, red skin with silvery scales.

According to the National Institute of Health, psoriasis is estimated to affect 2.0-2.6 percent of the U.S. population, with higher incidence in Caucasians.

About 15 percent of psoriasis patients may eventually develop psoriasis arthritis, a debilitating joint condition.

XenoPort said both 800 mg and 400 mg doses of the oral drug, XP23829, reduced the severity of psoriasis, the company said.

The U.S. Food and Drug Administration earlier this year approved Novartis' injectable drug, Cosentyx, for treating psoriasis. Eli Lilly & Co is also developing Ixekizumab for treating the disease.

Canada's Valeant Pharmaceuticals International Inc also bought rights to AstraZeneca Plc's late-stage experimental psoriasis drug brodalumab after it was dropped by Amgen Inc in May.