Amphastar Pharmaceuticals Inc said that the U.S. Food and Drug Administration had rejected its application to market an intranasal version of the emergency opioid-overdose treatment, naloxone.

The abuse of opioids a class of drugs that includes heroin and prescription painkillers has assumed epidemic proportions in the United States.

The Centers for Disease Control and Prevention (CDC) estimates that 91 Americans die every day from opioid overdoses. Last April, officials attributed the death of musician Prince to the accidental overdose of the synthetic opioid fentanyl.

The FDA's complete response letter identifies issues with user human factors study which is designed to evaluate the user interface of a product among others, Amphastar said.

Amphastar already sells naloxone in pre-filled syringes, as does privately held Kaleo Pharmaceuticals, which came under fire earlier this month for raising the price of its naloxone device Evzio by 550 percent to $4,500.

Adapt Pharma Ltd already has two nasal spray formulations approved by the U.S. FDA.