The Food and Drug Administration has asked for more information from an Australian pharmaceutical company before it approves a new type of painkiller that combines two widely prescribed opioids. The FDA sent a “Complete Response Letter” to  QRxPharma for more details about the safety and effectiveness of the drug, called MoxDuo.

MoxDuo is a prescription medication that combines morphine and oxycodone for the treatment of moderate to severe acute pain. QRxPharma claims that combining the two drugs into one medication will have a synergistic effect, reducing side effects and the need for higher doses.

“We remain confident in MoxDuo as a potential therapeutic option for the millions of patients suffering from moderate to severe acute pain and will continue our efforts to bring this therapy to market.” said Dr. John Holoday, QRxPharma’s Managing Director and CEO.

QRxPharma and its partner Actavis, a privately-held Swiss pharmaceutical company, were hoping to market MoxDuo for commercialization in the $2.5 billion acute pain market in the U.S. after getting FDA approval. MoxDuo would  be manufactured in three different forms; intravenous, controlled release, and immediate release to make it more widely available to pain patients.

“While we are disappointed by the Complete Response Letter, we are supporting of QRxPharma’s continued efforts to work with the FDA to fully address their questions in a timely manner,” said Doug Boothe, CEO of Actavis.

MoxDuo is touted to be more effective for moderate to severe acute pain than morphine or oxycodone alone. A pilot study of MoxDuo found that when compared to Percocet, a widely prescribed opioid, the immediate release form of MoxDuo was better tolerated by patients, with less hypotension, constipation, nausea, and vomiting.

The delay in FDA approval was a substantial setback for QRxPharma and its stock fell sharply on the Australian stock exchange. QRPharma, who has offices in Australia and the U.S., has a year to provide more information on MoxDuo’s safety and effectiveness, and to resubmit its application to the FDA. The company did not say if more clinical studies would be needed.