Nasdaq halted InterMune Inc. shares Tuesday as a Food and Drug Administration panel of experts reviews a key lung drug candidate.

The stock was halted at $23.30 in midday trading, ahead of the expert panels recommendation. On Friday, the FDA voiced "uncertainty" about whether the drug, pirfenidone, provides a meaningful benefit, considering there are no currently approved treatments for the condition idiopathic pulmonary fibrosis, a normally fatal lung disease.

The FDA has already reviewed the drug and is asking a panel of experts to vote on its safety and effectiveness. The agency isn't required to follow the advice of its panels, but often does. One potential sticking point is the potential for liver problems as a side effect of the drug.

InterMune, based in Brisbane, Calif., has stressed the need for the drug's approval, citing a lack of effective treatments on the market. It has said about 200,000 people in the U.S. and Europe have idiopathic pulmonary fibrosis, which causes scarring and stiffening of the lungs.

The FDA is scheduled to make a decision on the drug by May 4. If approved, the drug will be sold in the U.S. as Esbriet. It is already approved and sold in Japan as Pirespa by Shionogi and Co.

Leerink Swann Research analyst Howard Liang said the panel committee members' questions to the company don't seem "especially" critical so far. In a note to investors, he said the company addressed the issue of potentially damaging liver side effects by showing patients returned to normal liver function when doses of the drug were reduced or discontinued.

"The company noted clean safety experience since the drug's approval in Japan and proposed liver function monitoring in the label," he said.

Liang reaffirmed a "Outperform" rating for the stock.