Shares of Genelabs Technologies ( GNLB) doubled after the company received an approvable letter from the Food and Drug Administration regarding Prestara, a drug designed to treat lupus.

Recently, shares of Genelabs were up $1.48, or 106%, to $2.87.

Final approval on Prestara, developed by Genelabs and exclusively licensed to Watson Pharmaceuticals ( WPI) in North America, is contingent on the positive results of another clinical trial. Prestara was formerly called Aslera. Watson was up 19 cents to $23.28.

A previous Genelabs study had shown a positive effect on bone mineral density in women with mild to moderate lupus while on low-dose glucocorticoids. In the study, patients who received Prestara experienced increased bone mineral density. Those who received a placebo had reduced bone mineral density. The difference between the groups was "statistically significant," Genelabs said.

After the next clinical trial is completed, Genelabs and the FDA will meet to discuss the results of the study and address any remaining issues.

Lupus is an autoimmune disease that can damage the heart, lungs, kidneys, joints, nervous system and other parts of the body. No new drugs for treating the disease have been approved in the U.S. for more than 40 years.