** Shares of drug developer Alkermes ALKS.O rise 3.14% to $28.55 premarket

** Co says its experimental drug alixorexton has received breakthrough therapy designation from the U.S. FDA for treating narcolepsy type 1, a rare sleep disorder

** Narcolepsy type 1 causes excessive daytime sleepiness and sudden muscle weakness, says co

** FDA decision based on early-stage trial in 92 patients; drug helped patients stay awake longer vs placebo - ALKS

** A breakthrough therapy tag is meant to speed up development and review of drugs to treat a serious condition or unmet medical need

** Co's alixorexton is a once-daily pill targeting brain pathway that regulates wakefulness; late-stage trials start early this year - ALKS

** As of last close, stock down ~3% over the past year

(Reporting by Sahil Pandey in Bengaluru)

((Sahil.Pandey@thomsonreuters.com))