Avastin is primarily used to treat colorectal cancer.Handout
Patients taking the commonly used cancer drug Avastin could be at risk of developing flesh-eating disease, Health Canada is warning.
The maker of the drug, Hoffmann-La Roche Ltd., said a total of 52 cases of necrotizing fasciitis, the formal name for flesh-eating disease, have been identified in patients who took Avastin in the period from November, 1997, to September, 2012. More than one million patients were treated with the drug during that time, meaning that the risk is small.
To date, two Canadians taking bevacizumab (brand name Avastin) are known to have developed flesh-eating disease, including one who died. Worldwide, 17 cases were fatal.
The Canadian warning was issued on Monday in a standard "dear healthcare professional" letter, and was released publicly on Thursday. The U.S. Food and Drug Administration issued a similar warning about Avastin in March.
Most of the cases of flesh-eating disease occurred in patients who had surgery for colorectal cancer, and the infection is likely a complication of poor healing of wounds, which places patients at high risk of hospital-acquired infections.
Necrotizing fasciitis can occur when certain types of bacteria penetrate the skin and create toxins that eat away at muscle and fat tissue. To stop the spread of the bacteria, the treatment is often amputation of a limb.
Most of the affected cancer patients also had diabetes. Many also suffered from perforated bowels, another side effect of the drug.
In Canada, Avastin is licensed for treatment of advanced cases of colorectal cancer, lung cancer and a brain tumour called glioblastoma. It has been used previously to treat some forms of breast cancer but proved ineffective. Avastin is an angiogenesis inhibitor, meaning that the drug slows the growth of new blood vessels; cancers need blood to grow and the drug blocks the "feeding" process.
The new alert does not mean that patients should not be treated with Avastin. The drug is not being recalled.
The company said the product monograph – which explains how the medication should be used and the possible side effects – will be modified to reflect the new findings.
The company said flesh-eating disease is rare in patients taking Avastin, noting that in clinical trials and post-marketing studies, it affects between 1 in 1,000 and 1 and 10,000 users.
Avastin has been the subject of at least three other health alerts from Health Canada, including warnings about the risk of gastrointestinal perforation (a hole in the stomach of intestines), fistula formation (an abnormal passage from one body part to another) and blood clots.
Flesh-eating disease seems to be a secondary risk for those who suffer bowel perforation or fistula and the company is recommending that treatment be discontinued immediately if these complications arise.
Necrotizing fasciitis claimed the life of Muppets creator Jim Henson in 1990, and former Quebec Premier Lucien Bouchard, had part of a leg amputated because of flesh-eating disease in 1994.
People who have weakened immune systems, such as the elderly, people with diabetes and those with cancer are at higher risk for the condition.
Avastin is one of the world's top-selling cancer drugs with sales in excess of $2-billion in the United States alone. In Canada, a course of treatment for colorectal cancer costs about $40,000.
André Picard