Updated

Lawyers for a French pharmaceutical group suspected in the deaths of at least 500 people argued Monday that a trial against their client should be halted as two separate cases should be rolled into one before the court can proceed.

The trial of Servier on charges of "aggravated deception" opened in Nanterre, west of Paris just as a similar case is being investigated in the French capital over the diabetes drug Mediator.

The company is accused of hiding that Mediator — also used for weight loss — contained an amphetamine called benfluorex, which was taken off the market in 2009 after being found to thicken heart valves.

Servier lawyers argued against holding the Nanterre trial, claiming that the laboratory could not be judged twice on the same grounds.

"Your court can in no way rule on the core of this case," said defense lawyer Herve Temime, arguing that the investigation is not yet fully complete.

The court claims the nature of benfluorex was allegedly hidden to obtain approval for the drug, first marketed in 1976. So far, charges have been filed against seven people, including company founder Jacques Servier, now 90.

It alleges the drug, often prescribed as a hunger suppressant, was behind the deaths of between 500 and 2,000 people over more than three decades.

The court is expected to rule May 21 on whether the trial, which was previously expected to run through July 6, can continue.