Bayer and Johnson & Johnson have received a major boost with the news that panellists at the US regulator have recommended approval of the anticoagulant Xarelto, despite concerns over bleeding and potential liver damage.

The US Food and Drug Administration's Cardiovascular and Renal Advisory Committee voted 15 to 2 to whether the clinical data submitted by the firms showed a "favourable risk-benefit profile for [Xarelto] rivaroxaban" for the prevention of blood clots in knee and hip surgery patients. The decision surprised some observers, seeing as how staff at the FDA had expressed major concerns about the risks of taking the drug a couple of days earlier.

The committee looked at data from four main clinical studies that looked at more than 12,000 patients. Much of the data compared Xarelto, which if approved will be sold by J&J in the USA, to the gold-standard drug, Sanofi-Aventis’ injectable Lovenox (enoxaparin).

The studies show that while rivaroxaban, which targets the Factor Xa enzyme, was effective at stopping clots from forming, there also was a small but increased risk of bleeding. The committee has therefore recommended approval but noted that they could not rule out the possibility that rivaroxaban could cause liver damage.

Panel member Sidney Wolfe, director of Public Citizen's health research group, voted against rivaroxaban, expressing concern that if approved, many doctors would use Xarelto for long-term treatment without knowing if the drug might cause liver damage.

The FDA will make its final decision on Xarelto by May 28 and the agency usually follows the advice of its panellists. The drug is already approved in Europe and Canada for hip and knee surgery, a relatively small indication, but Bayer and J&J are investigating rivaroxaban in the more lucrative areas of stroke and acute coronary syndrome.