US regulators intend to rescind the "breakthrough therapy" designation for Merck & Co's hepatitis C combination treatment, a decision that could delay approval of the product by several months.

The Food and Drug Administration (FDA), which awards the designation "breakthrough to medicines it deems likely to demonstrate "substantial improvement" over existing drugs, said other new drugs are available.

Analysts told the news agency Reuters that Merck's two-drug treatment would likely now require a standard 10-month review.
FDA'S decision comes on the heels of its recent approvals of costly oral treatments for the liver disease from Gilead and AbbVie. The breakthrough therapy designation is meant for drugs that address an unmet medical need, but there are now two other cures for hepatitis C on the market, analysts said.
The US drugmaker said it plans to discuss the matter with the FDA and still expects to seek the green light in the first half of 2015. Merck said it believes findings from recently completed late-stage trials will support approval

Merck's treatment consists of a protease inhibitor called MK-5172 and an NS5A inhibitor called MK-8742 that together had received the FDA's "breakthrough therapy" designation.

In a recent mid-stage trial, the company's combination treatment cured 98% of previously untreated patients with genotype 1, the most common and hardest to treat variant of hepatitis C.

Faced with such potent competiton for hepatitis C medicines, Merck said in June announced it would ramp up its involvement in the lucrative field by buying Idenix Pharmaceuticals for $3.85 billion and combining the two companies' most promising drugs to produce a faster, more effective cure.