A drug developed by Ligand Pharmaceuticals for treatment of hepatitis C patients with low blood platelet counts and purchased by GlaxoSmithKline (NYSE: GSK) wins approval from the FDA.

Ligand shares rose the most in 14 months after the news was announced.

Ligand rose 14 percent to $19.07 at the close in New York, its biggest one-day gain since August 2011. The La Jolla, California-based company said today the Food and Drug Administration approved the medicine to enable hepatitis C patients with low blood platelet counts to take interferon therapy.

The company had sold the rights to the drug to London-based GlaxoSmithKline Plc, which will pay Ligand royalties. Of the 4.2 million people in the U.S. with hepatitis C, about 3.5 percent have low blood platelet counts that disqualify them from treatment with interferon.

“Otherwise very sick patients, who had little to no therapeutic options, will now have an opportunity to potentially receive treatment for hepatitis C,” John Higgins, Ligand’s chief executive officer, said in a statement.

Interferon is given as a weekly injection for a year, carries flu-like side effects, and cures roughly half of patients.

The Ligand treatment wasn’t tested with new, experimental therapies that don’t include interferon. Pharmaceutical companies led by Gilead Sciences Inc., Abbott Laboratories and Bristol-Myers Squibb Co. are developing pill-based hepatitis C treatments in a bid to replace interferon therapies.

GSK operates its North American headquarters in RTP.

[GSK ARCHIVE: Check out 10 years of GSK stories as reported in WRAL Tech Wire.]

(Bloomberg contributed to this report.)