A transdermal patch used to treat mild to moderate symptoms of dementia could also pose a risk of overdose, leading to nausea, hypertension, slowed heart rate or death.
Health Canada issued a warning Wednesday about rivastigmine, a transdermal patch sold under the brand name Exelon, after 129 cases of misuse of the drug were reported worldwide. Two of the cases caused deaths. As of Feb. 28, there have been three reports of misuse of the patch in Canada, according to the Health Canada warning.
The Exelon patch, sold by Novartis Pharmaceuticals Canada Inc., was approved for use in Canada in 2008 and is designed to treat mild to moderate dementia associated with Alzheimer's disease and Parkinson's disease. It's part of a class of drugs called cholinesterase inhibitors.
Nearly 18,500 prescriptions for the patch were dispensed in Canada in 2008, according to IMS Health Canada, a company that tracks the pharmaceutical industry. In 2009, that number increased to nearly 65,000.
Health Canada said problems with the Exelon patch occur when it is used incorrectly or erroneously. Incorrect use can lead to an overdose of medication and cause a series of symptoms that may even lead to death. The department is urging consumers and health professionals to follow directions, such as making sure only one patch is applied at a time to recommended locations on the body, such as upper arm or lower back. Patches should also not be cut into pieces.
But there are questions about whether the reported overdoses are isolated to patients misusing the patch.
A study by St. Michael's Hospital and the Institute for Clinical Evaluative Sciences in Toronto, published in September's Public Library of Science Medicine journal found patients taking cholinesterase inhibitors, such as the Exelon patch, had a significantly higher risk of being hospitalized with bradycardia, an abnormally slow heart rate that can cause serious health problems, than patients not taking those medications.
The study doesn't make mention of patients misusing their medication.
The researchers said the findings show these drugs carry a serious risk of adverse events and that they should be prescribed with caution.
Patient information posted on the Novartis website dated January 2009 also warns that possible side effects of the patch could include nausea, vomiting, hallucinations and problems with heart rhythm. But the company doesn't say those side effects are associated with patient error, even though similar symptoms are outlined in Health Canada's warning as being the result of misuse of the patch by the patient.
In another section of the patient information provided by Novartis, it mentions that overdosing on the medication can result in nausea, high blood pressure, hallucinations and low heart rate, all problems outlined in the Health Canada warning.
Officials from Novartis declined a request for a telephone interview yesterday , but said in an e-mail the company stands behind the safety of the Exelon patch.
"The safety of patients is our highest priority, and we have been working with health authorities worldwide to address potential medication errors that have come to light with increasing use of Exelon patch," the company said.