A proposed class-action lawsuit has been filed against five Canadian pharmaceutical companies alleging the firms may have been negligent in their manufacturing of the drugs and in quality control testing of raw material from their supplier in China.

On July 10, Health Canada recalled 28 blood pressure medications from five generic brands that use the ingredient valsartan. The Chinese firm that produces valsartan reported a contamination with N-nitrosodimethylamine (NDMA), which the International Agency for Research on Cancer has classified as a probable human cancer causing agent.

Zhejiang Huahai Pharmaceuticals, the Chinese company involved in the contamination, did not respond to a request for comment from CTV News.

The recall could impact 4.4 million Canadians who’ve been prescribed these drugs. Merchant Law Group LLP is now pursuing a nationwide class-action lawsuit alleging the five Canadian companies -- Teva Canada Ltd., Sandoz Canada Inc., Pro Doc Limitee, Sanis Health Inc. and Sivem Pharmaceuticals ULC -- might not have adequately tested their products. Charney Lawyers have also filed proposed national class-action and Quebec class-action lawsuits.

“You take the pill your doctor gives you. You pick it up at the pharmacy. You don't think that anything is going to happen,” patient Carla James told CTV News. “It’s just unbelievable.”

James has been taking one of the recalled drugs for years and is now part of the proposed lawsuit. She says when the pharmacy called to indicate there’d been a recall on her prescription, she was shocked.

“I was terrified,” she said. “I just didn't know what to do or what to think. All I could think is: ‘I better get to my doctor (as soon as possible).’”

While James has been able to find an alternative prescription, it appears others might not be so lucky. Reports suggest the recall has caused a worldwide shortage of numerous prescription medications.

The Canadian Pharmacists Association has put together a list to help doctors and other prescribers find other options for their clients.

Several unanswered questions remain about the recall, including how many of the drugs have been impacted and for how long. The only report so far about how the cancer-causing agent got into the medications suggests it was a result of the “manufacturing process.”

“What I would like to know that I haven’t been able to hear up to now is for how long this problem has been going on,” said Jacinthe Leclerc, a medical researcher with Universite du Quebec a Trois-Rivieres.

“The companies will need to be transparent to the public, telling them for how long the potentially contaminated pills were…available to patients and what are they going to do to prevent any further problems.”

Health Canada’s advice to those who may be affected:

Continue to take your medication if it contains valsartan, unless your doctor or pharmacist has told you to stop;

Contact your doctor and see if the recall impacts your medication; and

If your medication is part of the recall, contact your doctor to discuss the possible next steps.

With a report from CTV’s medical affairs specialist Avis Favaro and producer Elizabeth St. Philip