** Shares of specialty pharma firm Scienture Holdings SCNX.O rise 19.99% to $0.6472 premarket

** Co says U.S. FDA has approved a new high-dose nasal spray, Rezenopy, for treating opioid overdoses

** Says spray delivers 10mg naloxone to reverse overdoses from powerful opioids including fentanyl

** Adds SCNX holds exclusive U.S. sales rights; Summit Biosciences will manufacture the product

** Patent protection runs through February 2041; naloxone market worth $154 million, with 9.3 million units sold annually - IQVIA data

** As of last close, stock down ~92% over the past year

(Reporting by Sahil Pandey in Bengaluru)

((Sahil.Pandey@thomsonreuters.com))