When cold medicine containing a poison made in China killed nearly 120 Panamanians in 2006 and early 2007, Americans could take some comfort in the belief that a similar epidemic could never happen here, not with one of the best drug regulatory systems in the world.

Then last spring, hundreds if not thousands of pets died or were sickened in the United States by a Chinese pet food ingredient that contained lethal levels of melamine, an industrial product used to artificially boost protein levels. That was followed quickly by the discovery that Americans were brushing their teeth with Chinese toothpaste containing a poisonous chemical used in antifreeze.

Still, no Americans died from the chemical.

And then came heparin.

A hugely popular blood thinner used in surgery and dialysis, heparin turned out in some cases to contain a mystery substance that sophisticated lab tests earlier this month determined to be a chemically modified substance that mimics the real drug. The United States Food and Drug Administration has linked it to 19 deaths and hundreds of severe allergic reactions, though the agency is still investigating whether the contaminant was the actual cause.

What a difference a year makes.

After many near misses and warning signs, the heparin scare has eliminated any doubt that, here and abroad, regulatory agencies overseeing the safety of medicine are overwhelmed in a global economy where supply chains are long and opaque, and often involve many manufacturers.