By Susan Heavey

WASHINGTON, Sept 18 (Reuters) - U.S. presidential candidates Barack Obama and John McCain are reviewing their support for allowing individuals to import cheaper prescription drugs in light of tainted medicines and other goods made in other countries, their advisers said on Thursday.

Reimportation, as the practice is known, has been controversial for years, even as some supporters have arranged trips to Canada and Mexico for patients to stock up on cheaper medications.

But recent scares involving chemical-laced batches of baby formula and the blood thinner heparin -- both made in China -- have raised new concerns that safely bringing in additional medical products from overseas could be tougher than expected.

"Both candidates were in favor of reimportation and sort of subsequent to the heparin incident (there's) a lot less enthusiasm," said Dora Hughes, a health policy adviser to Democratic candidate Obama.

"We have a better understanding of the challenges that go along to support the importation," she said, speaking before the Generic Pharmaceutical Association's (GPhA) annual conference in Washington.

Neither adviser said their candidate had abandoned reimportation, but had realized it would be more difficult.

"We now realize the challenges for doing that are greater than before," Douglas Holtz-Eakin, a senior policy adviser to Republican candidate McCain, told reporters at the conference.

Groups representing brand-name and generic drugmakers, including GPhA, oppose reimportation, saying it could allow more unsafe products into the country.

Canada and some other countries have lower prices for many prescription drug because of government price controls. Several U.S. bills have proposed allowing some importation for personal use but have never become law.

Since then, problems with numerous foreign products have raised new questions about how to import medications safely.

Most recently, more than 6,000 infants in China have fallen ill and at least three have died so far from milk powder contaminated with the chemical melamine, in a widening scandal that erupted earlier this month.

Sales of Chinese-made formula are banned in the United States, but U.S. officials have said some formula may have slipped into the country.

In February, the U.S. Food and Drug Administration reported the first deaths in U.S. patients given heparin made by Baxter International Inc <BAX.N>. The agency later acknowledged it had failed to inspect the Chinese facility where the drug's raw ingredient was made.

Pet food, toothpaste and other Chinese-made products have also drawn U.S. warnings. Critics have chided the FDA for its inability to properly inspect overseas manufacturers.

FDA officials have said they lack enough staff and money to regularly inspect such facilities. (Reporting by Susan Heavey; Editing by Tim Dobbyn)

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