US drugmaker Merck & Co unveiled a rather double-sided interim analysis from a 34,000-patient clinical trial of its COX-2 inhibitor Arcoxia (etoricoxib) yesterday, which showed that the drug did not increase the risk of cardiovascular events compared to the traditional painkiller diclofenac, but that more participants dropped out of the study because of high blood pressure.

A final analysis of the data will submitted to US regulators to satisfy their request - issued in 2004 - for more information on Arcoxia’s safety profile, although Merck has not disclosed when it expects this to be.

The drug’s development in recent years has been anything but smooth. Merck originally filed Arcoxia with the US Food and Drug Administration back in 2002, but then promptly withdrew its application to enhance its safety and efficacy profile, eventually re-filing the agent in early 2004. But later that year the agency issued an approvable letter seeking further information on the drug’s safety, pushing back its potential market launch yet again. The drug is, however, approved in over 60 countries around the world.

A follow-up to the company’s once very popular Vioxx (rofecoxib), pulled from the market in 2004 after data showing an increased risk of heart attack and stroke, Arcoxia is important to Merck in many ways. It offers the advantage of being kinder on the stomach than members of the non-steroidal anti-inflammatory class of painkillers, but industry observers are starting to question the firm’s costly pursuit of getting the drug to market in the US, given that if it does get there, sales could be held back by old fears over its lineage, as well as concerns over potential side effects.