Drug reviewers said a painkiller developed by Zogenix Inc. could possibly be abused more than currently available hydrocodone combination products.

Zogenix's painkiller Zohydro is a single-entity product containing hydrocodone -- a narcotic painkiller. Hydrocodone and oxycodone are often-abused drugs.

Combination hydrocodone drugs usually also contain acetaminophen, the active ingredient in common pain products such as Tylenol.

However, since an overdose of acetaminophen can cause liver damage, especially in patients on other acetaminophen medications, there is a requirement for painkillers without acetaminophen.

The reviewers said the expected higher levels of abuse with Zohydro were based on what has been observed for oxycodone products, according to briefing documents released by the U.S. Food and Drug Administration on Wednesday.

"The abuse ratio for oxycodone combination products was 24 emergency department visits per million tablets dispensed, compared with 85 visits for oxycodone single-entity ER products," the FDA reviewers said in the documents.

An independent panel of experts will advise the FDA and vote on the drug's safety, efficacy and approval on Friday.

Zogenix shares were down 6 percent at $2.39 in early trade on Wednesday on the Nasdaq.