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The only drug safe for pregnant women with serious thyroid disorders to take in the first trimester is no longer available in Canada, leaving doctors, medical organizations and the federal government scrambling to secure an alternative supply.

The discontinuation of the drug, propylthiouracil, known commonly as PTU, poses a major risk to pregnant patients with hyperthyroidism – or an overactive thyroid – caused by Graves’ disease, said Lois Donovan, endocrinologist and clinical professor at the University of Calgary’s Cumming School of Medicine. Graves’ disease is an autoimmune disorder that causes the thyroid to become overactive, and without treatment it can lead to heart, bone and other serious health problems.

“The downstream effects of not having this medication available are serious,” Dr. Donovan said.

The only alternative drug available, methimazole, causes birth defects in up to 10 per cent of pregnant women who take it during the first trimester, she said. The other treatment options, radioactive iodine and surgery, aren’t feasible either. Radioactive iodine is not safe to take during pregnancy and most operations have been postponed and delayed as a result of COVID-19, Dr. Donovan said.

Going without treatment increases the risk of miscarriage, premature birth, fetal heart problems and, in extreme cases, death of the mother and baby, Dr. Donovan said.

Until there is a solution in place, Dr. Donovan said she’s advising some patients with Graves’ disease to avoid pregnancy because of the potential risks.

“It certainly is upsetting,” she said. “We’ve talked about the alternative options, but most of those involve waiting … until we get a reliable source of this medication.”

Health Canada added PTU to its Tier 3 drug shortage list late last month. The list is reserved for shortages that “have the greatest potential impact on Canada’s drug supply and health care system.”

In an e-mail, a Health Canada spokesperson said the department is aware that some patients are having problems accessing the drugs and that it’s working to help secure another supply, such as from a foreign country.

Stan Van Uum, president-elect of the Canadian Society of Endocrinology and Metabolism, said he had a call with Health Canada officials Monday to discuss options to address the discontinuation. Dr. Van Uum said the federal government has identified a supply source outside of Canada, but it’s unclear how long it could take to get the drug here. The CSEM first wrote to the federal government about the drug discontinuation in late April.

Dr. Van Uum said the sudden discontinuation of PTU also exposes the long-standing issues with drug shortages and discontinuations in Canada – problems that need to be addressed urgently, Dr. Donovan said.

“I think it shows the vulnerability of a system where they’re dependent on one single supplier for a drug,” he said. “I think the approach at the moment, it’s not pro-active. It’s waiting until there is a signal that there is a shortage.”

It’s unclear why PTU has been taken off the market, but sudden shortages and discontinuation of various prescription drugs have become increasingly common in Canada. Manufacturers say problems such as sourcing raw ingredients and supply chain issues are often to blame.

In mid-December, Paladin Labs posted a discontinuation report for PTU on the website The company did not respond to an interview request on Monday.

But many clinicians didn’t start hearing about the sale stoppage for several more weeks. Dr. Donovan said she started to hear about the discontinuation from patients in March. Last week, one of Dr. Donovan’s patients who is in the early weeks of pregnancy was able to find a pharmacy that still had some PTU in stock. But this isn’t a viable solution for most patients, she said.

“If I can’t get a hold of it … to be honest, I’m not going to accept that answer because we need it.”

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