The $50 million compensatory damage award in a federal Vioxx case this month was “grossly excessive,” and a new trial must be held to decide how much drugmaker Merck & Co. must pay a retired FBI agent who suffered a heart attack after taking the painkiller, a federal judge ruled Wednesday.

New Jersey-based Merck said it was pleased with the decision on the damage award, and said it would ask the judge to order a new trial on whether it was liable in the case as well.