The surprise finding earlier this year that a $76 heart attack drug is just as good as one costing 29 times more has been called into question by new research.

The latest report bolsters the widespread skepticism among U.S. physicians that greeted the release of a major Italian study finding that the two clot-dissolving medicines are equally effective.Both drugs are intended to break up clots that plug that hearts' arteries during heart attacks. If these clots are removed within four hours or so, victims may escape permanent damage to their hearts.

The chief rivals for this lucrative market are TPA, which costs $2,200 per treatment, and streptokinase, which costs $76. Early U.S. studies suggested that TPA worked better, and the medicine quickly gained about two-thirds of the U.S. market share.

"The real issue around the world is whether streptokinase is comparable to TPA," said Dr. Judith Hsia, principal author of the latest report. "It's much cheaper, and many countries, including the United States, would prefer to give it if it is just as good."

Some thought that issue was settled last March when an Italian study of 12,490 men found that the two drugs "appear equally effective and safe for use in routine conditions of care."