Cancer patients affected by watered-down chemotherapy drugs at five hospitals, including four in Ontario, have retained a law firm for a class-action suit against the drug supplier, Mezentco Inc. of Hamilton.

The drugs in question, cyclophosphamide and gemcitabine, are alleged to have been diluted between three and 20 per cent and administered for at least a year to nearly 1,200 patients, Sutts, Strosberg and Siskinds LLP said in a release on Wednesday.

“We believe that through this class action, the defendant will be required to account for the problem with these drugs, explain to Canadian patients how this problem occurred, and compensate those affected,” lawyer Mike Peerless said.

Meanwhile, the five hospitals — four in Ontario and one in New Brunswick — are in the process of contacting the cancer patients who received the drugs.

Cancer Care Ontario says the patients were treated at London Health Sciences Centre, Windsor Regional Hospital, Lakeridge Health and Peterborough Regional Health Centre.

Ontario patients received lower than intended doses of both cyclophosphamide and gemcitabine.

Saint John Regional Hospital in New Brunswick says 186 patients received lower than intended doses of cyclophosphamide.

The drugs were used as far back as February 2012 at the Windsor hospital and March 2012 at the London hospital. The Saint John hospital says it had purchased the drugs since March 2012.

Affected patients are being encouraged to discuss the possible effects of the underdosing with their oncologists.

Ontario Health Minister Deb Matthews noted about 7.5 per cent of cancer patients being treated at London Health Sciences Centre were affected.

“People have to talk to their oncologist,” Matthews said Tuesday. “I wouldn’t want people to panic about it because every patient will need that conversation with their oncologist to determine if they might need additional chemo treatments or whatever.”

The hospitals purchased the drugs from the supplier and are now working to determine the cause of the error.

Cancer Care Ontario says all four Ontario hospitals immediately stopped using the medications when the problem was discovered late last month and informed the manufacturer of the error.

Each hospital has secured new supplies of the medications and Cancer Care Ontario says patients’ treatment cycles will not be interrupted.

“It’s important to note that chemotherapy preparation and delivery is a complex process and as a result of this complexity, there are sources for potential error,” Dr. Carol Sawka, Cancer Care Ontario’s vice-president of clinical programs and quality initiatives, said in a statement.

“We have put in many steps to minimize these potential sources of error and we will continue to ensure that patient safety and high quality care are the focus and the strength of the system.”

The underdosing affected 665 patients at London Health Sciences Centre, 290 patients at Windsor Regional Hospital, 34 at Lakeridge Health, and one patient at Peterborough Regional Health Centre.

For more information on the class-action suit click here.

With files from CityNews.ca staff