Close to 300 patients at Windsor Regional Hospital were given the wrong dosage of chemotherapy for a duration of a year, hospital officials confirm.

According to a statement from Cancer Care Ontario, four Ontario hospitals are informing 990 patients that they received lower than intended doses of cyclophosphamide and gemcitabine.

The hospitals affected are London Health Sciences Centre, Windsor Regional Hospital, Lakeridge Health and Peterborough Regional Health Centre.

It impacted 290 patients in Windsor, 665 in London, 34 in Oshawa and one in Peterborough.

“This watering down of this particular chemotherapy drug will have an individualized impact on every single patient," says Windsor Regional Hospital CEO David Musyj.

In the compounded process, the pharmaceutical company did not adjust for the overfill present in IV bags and as a result the products are of a lower concentration than labelled, according Musyj. This resulted in a three to 13 per cent lower dosage being administered to the 990 patients, starting in February 2012.

"What you're supposed to do, because these bags are overfilled, is you're supposed to extract all of the saline solution from them or start with an empty bag," says Musyj.

At this time, the hospital cannot release the name of the pharmaceutical company involved. Musyj says it was health care worker in Oshawa that made the discovery.

“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,” says Dr. Carol Sawka, vice president of clinical programs, Cancer Care Ontario.

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

Cancer Care Ontario says each case is patient-specific and affected patients are being encouraged to discuss the possible effects of the under-dosing with their oncologists. The organization says it is working with the affected hospitals and the supplier in order to find out the exact cause of the error.

Patients and family members in Windsor impacted by this issue can call (519) 255-8698 for support.