Severe side effects prompt warnings on cancer drug

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TORONTO — Avastin, a drug approved in Canada to treat advanced colorectal cancer, has been linked to two serious complications in a small number of patients, the drug's manufacturer advised Friday.

But Avastin, which works by choking off a tumour's blood supply, is also being tested experimentally for prostate, kidney, pancreatic and ovarian cancer, and is being widely used off-label by eye doctors to treat one form of age-related macular degeneration. (Off-label means doctors can prescribe any approved medication for other purposes.)

Most patients who experienced either of the two complicating conditions red-flagged Friday — hypertensive encephalopathy or RPLS — were being treated for conditions other than advanced colorectal cancer, Hoffmann-La Roche Ltd. said in an advisory to health professionals and the public on Health Canada's website.

Three confirmed cases of hypertensive encephalopathy linked to the drug have been reported worldwide. The company is advising doctors to permanently discontinue the drug in patients who develop the condition, which is marked by severely high blood pressure associated with headache, nausea, vomiting, convulsions or confusion.

In all cases (none in Canada), patients had a medical history of elevated blood pressure. One person died. Hypertensive encephalopathy may be reversed if treated by progressively reducing blood pressure to near normal ranges within several hours.

There are also reports of patients on Avastin developing RPLS (reversible posterior leukoencephalopathy syndrome), a rare neurologic disorder that can cause seizures, headache, altered mental status and visual disturbance. The company is advising doctors to discontinue Avastin in patients who develop RPLS, which may be reversible if recognized and treated promptly.

Four confirmed and 10 suspected cases of RPLS have been reported among patients taking Avastin worldwide, including one suspected case in Canada. The onset of symptoms occurs between 16 hours and one year after starting the drug.

Avastin is Roche's fifth bestselling drug, with sales of US$1.7-billion last year. The medication is increasingly used off-label to treat older patients with wet macular degeneration because it costs at least 10 times less than U.S.-approval Lucentis, a drug that could be given the go-ahead in Canada as early as next year.

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