The European Commission has ordered a full-scale probe into the safety of five remaining Cox-2 arthritis drugs, following last month’s worldwide withdrawal of Merck & Co Inc.‘s Vioxx.

Vioxx - a blockbuster drug with annual sales of $2.55 billion - was pulled from the market after a clinical study showed it raised the risk of heart attacks and strokes.

The London-based European Medicines Agency said on Friday it had been given the go-ahead for the investigation after a preliminary review established there were serious safety questions.

Its remit will now include Novartis AG’s new Cox-2 drug Prexige, which was not covered by the earlier short review. Prexige is on sale in Britain and Australia but not yet approved elsewhere in the European Union or the United States.

“We think there is a public health issue here that needs to be sorted out and the Commission has now given us a formal, legal mandate to do it ... with a binding outcome,” agency spokesman Martin Harvey said.

The agency gave no timeframe for the investigation but Harvey said it would take months rather than weeks, putting it on a par with a parallel investigation by the U.S. Food and Drug Administration.

The FDA plans an advisory committee to review the safety of the Cox-2 drug class in January.

“We are obviously going to be as quick as we can because these products are on the market and people are being prescribed other drugs as an alternative (to Vioxx),” he said.

Cox-2 inhibitors were launched in late 1990s as an alternative to older non-steroidal anti-inflammatory drugs such as ibuprofen and naproxen, which can cause stomach damage. They quickly became some of the world’s best-selling medicines.

SHOCKWAVES

Merck’s decision to pull Vioxx sent shockwaves through the industry and has raised fears about the safety of other drugs in the same class.

So far, however, makers of competing products say they do not see evidence of similar cardiovascular dangers with their medicines.

The European drug agency’s scientific committee responsible for human medicines previously reviewed the Cox-2 inhibitor class in 2003, but will now be reviewing newly available data.

The panel will look at all aspects of cardiovascular safety of the Cox-2 inhibitors, including thrombotic events, such as heart attack and stroke, and cardio-renal problems, such as high blood pressure, fluid retention and heart failure.

The other big Cox-2 drug maker is Pfizer Inc., which sells market leader Celebrex, as well as Bextra and Dynastat. The latter is used mainly to treat pain in hospitals.

Pfizer announced earlier this week it planned a major new study to establish the safety of its best-selling drug.

The final drug covered by the European agency probe is Merck’s Arcoxia - a follow-up to Vioxx - which is approved in Europe but not in the United States.