* FDA panel votes 18-1 in favor of RBP-6000
* FDA decision due by Nov. 30; rival product close behind
* Indivior shares jump 11 percent (Adds further sales forecasts, latest share price, details)
Nov 1 (Reuters) - Indivior's experimental drug to help fight America's growing opioid addiction crisis has been recommended for approval by a U.S. advisory panel, boosting its sales prospects as competitors threaten revenues from an older product.
Shares in the London-listed company, which specializes in addiction treatment, were 11 percent higher by 0855 GMT on Wednesday on the overnight news, extending gains this week.
The advisory committee to the U.S. Food and Drug Administration (FDA) voted 18-1 that Indivior's injectable drug, known as RBP-6000, could benefit addicts and the lower of two doses studied had an acceptable safety profile.
The FDA, which is due to make a decision on the medicine by Nov. 30, typically follows the recommendations of its advisory panels.
The endorsement comes less than a week after FDA Commissioner Scott Gottlieb announced the agency's plans to encourage widespread use among opioid addicts of less harmful opioids such as methadone and buprenorphine, the active ingredient in RBP-6000.
"I think this is a really promising alternative to what's out there and will be attractive to a lot of patients," said Laurel Habel, a panelist and researcher at Kaiser Permanente in Oakland, California.
The United States is battling an opioid abuse epidemic that in 2015 killed 33,000 people. President Donald Trump recently declared the problem a national public health emergency.
Indivior studied two dosing regimens. In one, 300 milligrams were given once a month for six months. In the other, two doses of 300 milligrams were followed by four doses of 100 milligrams. There was little difference in effectiveness between the two doses and the higher dose caused more side effects.
Panelists said they would like to see more data about which patients should be given the higher dose, though some said they would like to have it available despite the lack of data supporting any additional benefit.
If approved the product would be the first monthly injectable buprenorphine treatment. Indivior already sells Suboxone Film, a product which combines buprenorphine and nalexone and is placed under the tongue or inside the cheek.
Two months ago Indivior shares plunged following a U.S. court ruling that cleared the way for a generic rival to Suboxone Film.
Stifel analyst Max Herrmann said RBP-6000 could capture about 30 percent of the broader buprenorphine market and he expects it to generate annual sales of around $700 million by 2021. Jefferies sees potential peak sales of $1.3 billion by 2025.
Lund, Sweden-based Camurus and privately held Braeburn Pharmaceuticals are also awaiting the health regulator's decision on their weekly and monthly injectable buprenorphine drug, CAM2038.
Herrmann forecast these once-monthly formulations, RBP-6000 and CAM2038, to garner around 50 percent of the buprenorphine market, just short of the 56 percent Suboxone currently enjoys. (Additional reporting by Divya Grover and Justin Varghese in Bengaluru; Editing by Shounak Dasgupta and Mark Potter)