Federal health advisers on Tuesday backed the experimental drug from InterMune Inc., despite mixed evidence of whether it poses significant benefits for patients with a rare lung disease.

It also quoted that it should be approved for patients with the rare fatal condition, and the shares rose 63 percent in after-hours trading.

The Food and Drug Administration's panel of lung experts in a 9-3 vote revealed that data extends a strong evidence to support use of the drug, pirfenidone, for patients with idiopathic pulmonary fibrosis (IPF).

However, the final decision made by the agency is revealed to be out by May 4.

"IPF is a fatal disease and you have to offer your patients hope", said Karen Gottesman, the panel's patient representative. "If this drug can offer your patients even a smidgen of hope, it's worth approving".

Intermune extended two studies for its drug to FDA, posing the ability to improve lung function in patients.

One study reported a statistically significant 4.4 percent rise in lung strength, however, another failed to achieve significance compared with placebo.