Valeant Pharmaceuticals International Inc's experimental drug to treat the skin disorder psoriasis carries a potential risk of suicide that is challenging to assess due to limited data, according to a preliminary review by the U.S. Food and Drug Administration published.

The review comes two days ahead of a meeting of outside experts who will advise the FDA on whether the drug should be approved. The agency is not obliged to follow the advice of its advisory panels but typically does so.

In clinical trials of the drug, brodalumab, there were six suicides across all programs: four in psoriasis studies, one in a rheumatoid arthritis study and one in a psoriatic arthritis study.

"We have uncertainty about whether the signal for completed suicide is a risk related to brodalumab treatment," FDA reviewers said. "From the available data, we cannot conclude whether or not suicide is a drug-related risk."

If approved, brodalumab has the potential to be used in a large number of patients in the United States and likely prescribed by a doctor that may not be familiar with screening for and diagnosing suicidal thinking and behavior, the reviewers said.

There are several risk management options that could provide some assurance that doctors and patients understand the safe use conditions of taking the drug.

"However, no risk management strategy will completely eliminate the risk" they said.

Brodalumab, was initially developed by AstraZeneca Plc and Amgen Inc. In May, 2015, Amgen withdrew from the partnership after trials revealed the potential suicide risk.

AstraZeneca subsequently licensed global rights to the drug to Valeant, whose fortunes have plummeted over the past year amid criticism of its high drug prices and suspect relationship with a specialty pharmacy.

AstraZeneca recently terminated Valeant's license to market brodalumab in Europe and signed an exclusive license instead with Denmark's LEO Pharma.

Before the trial results, AstraZeneca said brodalumab could generate annual sales of up to $1.5 billion a year. David Maris, an analyst at Wells Fargo, recently projected it would, if approved, generate just $250 million by 2020.

"Given the drug's safety profile, we expect a challenging commercial launch," he said in a research report.

Brodalumab is known as an interleukin-17 inhibitor. Other drugs in the same class include Novartis AG's Cosentyx and Eli Lilly & Co's Taltz.

The drug would also compete with Amgen's Enbrel and AbbVie's Humira.