Adds details on disease in paragraphs 2 and 4, GSK executive comment in paragraph 3

March 19 (Reuters) - The U.S. Food and Drug Administration approved GSK's GSK.L drug for severe relentless itching caused by a type of liver disease, the company said on Thursday, making it the first treatment greenlit for the condition.

The drug, branded Lynavoy, was approved for patients with primary biliary cholangitis. Existing therapies do not directly address severe itch or cholestatic pruritus.

"The approval of Lynavoy in the US gives patients a much needed treatment option that offers rapid, significant and sustained improvement in the debilitating effects of itch caused by PBC," said GSK executive Kaivan Khavandi.

PBC is a chronic disease where the body's immune system mistakenly attacks and destroys the small bile ducts in the liver. It affects more than 100,000 adults in the United States, according to National Institues of Health data.

The company did not immediately respond to Reuters request for comment on pricing and availability details.