A national shortage of a popular drug used to treat high blood pressure is raising concerns among Canadian doctors about the lack of backup systems to protect patients' supply.

Bayer Canada is reporting a temporary shortage of Adalat XL, an extended release formulation of nifedipine that is usually available in 20 milligram, 30 milligram, and 60 milligram tablets.

The drugs, known as calcium channel blockers, are used to treat hypertension and forms of heart disease, including angina. The 20 milligram and 60 milligram dosages are affected by the shortage.

It's a commonly prescribed medication in Canada. More than 145,000 prescriptions for Adalat XL were filled among recipients of Ontario's Drug Benefit program between February and April 2018 alone.

"We have a problem with drug shortages," said Dr. Christopher Labos, a cardiologist in Montreal.

"We don't have a system in place to correct for that and this happens with different types of medication every so often."

In the case of Adalat XL, a generic alternative is available from the same subclass of medication. But that's not always the case.

'Solutions exist'

Labos couldn't believe it the first time a pharmacist told him a shortage of another medication for arrhythmia meant there was nothing he could give to a patient.

He likened the shortages to a trip to a grocery store.

"We assume that there will always be food at the grocery store, but we forgot that we actually have to grow the food [and have] a distribution system to get it to the grocery store. Things can go wrong with that," Labos said.

Similarly, safeguards also need to be put in place for the country's drug supply, he said.

Labos said that for some generic medications, backup plans could include legally binding contracts that stipulate if one company isn't able to manufacture a drug, they need to ensure its made elsewhere.

Government stockpiles, such as for flu medications, are another option, although the drugs do expire.

"Solutions exist. It's just that none of them are easy," Labos said.

The logo of Bayer AG is pictured at the facade of the historic headquarters of the German pharmaceutical and chemical maker in Leverkusen, Germany on May 14, 2019. The company said the Adalat XL shortage occurred after it received a warning letter from the Food and Drug Administration following an inspection of the German plant. (Wolfgang Rattay/File Photo/Reuters)

In an email to CBC News earlier this month regarding a shortage of three vital cancer drugs, Health Canada said it "recognizes the impact that these shortages have on the patients who rely on these important medications and is taking action to address them."

The department said it monitors drug shortages closely.

Bayer Inc. said the Adalat XL shortage occurred after it received a warning letter from the U.S. Food and Drug Administration last year following a routine inspection at the company's Leverkusen Supply Center in Germany.

FDA officials found problems with "Good Manufacturing Practices," which are are quality-control standards.

Bayer said it is modernizing the plant to remediate.

"We are committed to helping health-care professionals access these products, and will provide updates as new information becomes available," the company said in a statement.

"Patients who are prescribed these products should speak with their health-care professional to determine the best solution for them."

Shortages 'notable in hypertension'

Dr. Ross Feldman, a cardiologist in Winnipeg, said drug shortages increasingly are a concern.

"Generally we know that shortages disrupt patient care," he said. "It's especially notable in hypertension."

The Canadian Pharmacists Association says drug shortages have increased in the last three to five years, leaving pharmacists to spend more time discussing alternative medications, finding alternatives, and calling around to track down supplies.

The worst-care scenario would be having to switch a patient off a drug that works for them if there's no alternative, said Mina Tadrous, a pharmacist and scientist at Women's College Hospital in Toronto.

"We really have no understanding of what happens when a bunch of people start switching drugs," he said. As a researcher, he's planning studies to try to find out.

"The hope is that it doesn't lead to any harm but there is potential."

Bayer estimates its current Adalat XL shortage will end on Sept. 15. The company also anticipates the 30 milligram tablets will run short at the end of August for one month.