Vertex Pharmaceutical's shares climbed more than 10% on news that US Food and Drug Administration advisors consider its drug telaprevir to be effective in treating patients with hepatitis C, moving it a step closer to approval.

According to documents posted on the regulator's website ahead of an advisory committee meeting on April 28, at which the medicine's risks and benefits will be discussed, health officials said adding Vertex' drug to standard therapies was effective in more patients with the disease and at a faster rate than standard treatment alone.

The documents note that in one study telaprevir 79% of newly treated patients achieved a sustained virologic response versus 44% of those on standard treatment, which is actually a higher than the 75% previously reported by Vertex because regulators used a different efficacy calculation method. 

It is widely believed that the drug will now secure all-important US approval, given its strong efficacy and relatively minor safety issues.

Vertex will be breathing a sigh of relief particularly as Merck & Co is also racing to get its rival new hepatitis C drug boceprevir - which will be under review by the FDA's Antiviral Drugs Advisory Committee on April 27 - onto the US market.

Both drugs block the action of the enzyme protease, which enables reproduction of the hepatitis C virus, and thereby offer a different approach from veteran therapies which are designed to boost the immune system as a means of fighting the disease

Analysts are expecting both telaprevir and boceprevir to rake in sales of over $1 billion.