Two American senators are urging federal Health Minister Rona Ambrose to stop the production in Canada of a form of oxycodone that is easily abused and has been flowing to drug users in the United States where it is banned.

Ms. Ambrose suggested last October that she might take steps to join the United States in outlawing a form of the prescription painkiller, marketed as OxyContin and known as hillbilly heroin, which is easy to crush, dissolve, inject or snort. Deaths related to opioids of this sort have tripled in North America since 1990.

But months after Ms. Ambrose's vague promise to create a new prescription drug strategy that would include measures to stop the abuse, nothing concrete has been done. And appeals by the U.S. drug czar for Canada to allow only the tamper-resistant form of the painkiller to be manufactured in this country have gone unheeded.

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The issue is becoming a significant irritant for American politicians who are taking steps to curb the problem in their own country only to see their efforts undone by Canada.

In a letter dated March 26, Tom Coburn and Richard Burr – two Republican senators involved in health issues – say it is their hope that Health Canada and the U.S. Food and Drug Administration "will appropriately collaborate and co-ordinate their respective regulatory approaches to this issue."

The importance of such co-ordination is underscored, write the senators, "by the proximity of our nations whereby drugs can easily cross the border, either legally or illegally, including non-abuse-deterrent formulations of opioid drugs."

Ms. Ambrose said in an e-mail to The Globe and Mail on Wednesday that prescription drug abuse is a growing problem in Canada. But, in terms of addressing the concerns of the U.S. senators, the minister would say only that she is looking at tamper resistance as a way to address prescription drug abuse.

"We have been working with the U.S. and exchanging information," Ms. Ambrose wrote. "We will continue to work with all partners to combat this issue together and ensure we make the right decisions based on sound evidence."

A study by the Ontario Drug Policy Research Network found that the amount of abuse-prone OxyContin moving into the United States at the Detroit-Windsor tunnel spiked between August, 2010, and February, 2012, after the U.S. moved to the tamper-resistant formulation. The network is now looking at the amount flowing at border crossings across Canada.

The OxyContin pills going to the U.S. "are legal prescriptions that are being filled in retail pharmacies [in Canada], but the vast number of pills that are being dispensed suggests they are not being dispensed for legitimate prescribing purposes," said Tara Gomes, the lead scientist on the studies. "It suggests that people are coming across the border, getting prescriptions and having them filled in Ontario, and then taking those drugs back across the border, likely for sale."

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Edward Lawrence, a business professor at the University of Missouri who watches the prescription drug trade, said the health cost of oxycodone abuse in the United States is "tremendous." Users who don't kill themselves often end up in hospital for weeks after overdoses, he said.

"We have been doing everything in the U.S. to try to cut back on the more abuse-prone formulations and they have been closing the door," said Dr. Lawrence. "But, as long as Canada continues to allow it in the other form, it's going to come across."