The Globe and Mail
A class of drugs commonly used to treat diabetes doubles the risk of heart failure, according to a new study.
The findings, published in the journal Diabetes Care, are sure to increase the scrutiny given to thiazolinediones, or TZDs, which are among the world's bestselling drugs.
Earlier this year, research showed that TZD sold under the brand name Avandia sharply increased the risk of heart attack and death from cardiovascular causes. The drug's manufacturer, GlaxoSmithKline, has rejected that research by presenting data showing Avandia is no more dangerous than other oral diabetes drugs.
The U.S. Food and Drug Administration has warned that Avandia should not be taken in conjunction with insulin. The FDA has also appointed an independent panel to decide if Avandia should be pulled from the market, or remain available with sterner health warnings.
The latest findings will be of great interest to the almost three million Canadians who suffer from Type 2 diabetes, which is primarily a lifestyle disease triggered by obesity and lack of exercise, though aging and genetic predisposition also play a part.
Diabetics have high levels of blood glucose and difficulty controlling insulin levels. This leads to damage to blood vessels and the cardiovascular system. Thiazolinediones such as Avandia (and its variants Avandamet and Avandaryl), and Actos help patients control their diabetes by decreasing the production of glucose and increasing muscle and liver use of insulin.
But TZDs also cause fluid retention, which can trigger heart failure in some diabetics, said Sonal Singh, an assistant professor of internal medicine at Wake Forest University in Winston-Salem, N.C., and lead author of the study.
The new findings are a meta-analysis, a compilation and analysis of earlier studies involving more than 78,000 patients. The study showed the risk of heart failure was double among those taking TZDs.
Dr. Singh and his team estimated that one additional patient with Type 2 diabetes would develop heart failure for every 50 taking the drugs for a period of just over two years.
The study showed that heart failure (common in the elderly) occurred regardless of the age of people taking the diabetes drugs.
It also showed that heart failure occurred quickly - within 24 weeks of starting the drugs - and that the effects may not be reversible.
Finally, patients taking low doses of TZDs appeared to have the same risks as those taking higher doses.
"The occurrence of heart failure several months after initiation of treatment suggests a long-term effect of the drugs, which may not be avoided by beginning with low doses," Dr. Singh said.
In Canada, doctors issued more than 14.3 million prescriptions for TZDs last year, with a retail value of $546-million, according to IMS Health, a private company that tracks prescription drug trends.
According to IMS Health data, the drugs are prescribed principally by family physicians, and the patients receiving them are largely in the 40-to-59 age group (40 per cent) and 65-and-older age group (32 per cent.)
About one in 11 Canadian adults suffer from Type 2 diabetes.
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