Singapore: Canadian scientists have revealed that the diabetes drug pioglitazone, also known as Actos, doubles the risk of bladder cancer. However, the researchers found that in absolute terms the risk remains low, equivalent to an extra 137 cases per 100,000 person-years.

The US FDA had in June 2011 warned that taking Actos for a year increased the risk of bladder cancer by at least 40 percent. FDA also ordered the drug's manufacturer, Takeda Pharmaceutical, to make a note of the same on the drug's label. The researchers, however, found no increased risk for patients taking Avandia.

The conclusion was reached by the team of scientists, which was headed by Dr Laurent Azoulay, epidemiologist, Jewish General Hospital, Montreal, who examined data from the General Practice Database containing the patient records from more than 600 general practices in the UK. The team studied 115,727 newly treated patients with diabetes drugs and matched each bladder cancer case to 20 healthy controls.

The team reported in the British Medical Journal, that 470 patients were diagnosed with bladder cancer in the average 4.6 years of follow-up, a rate of 89 cases per 100,000 person-years. The rate of bladder cancer in the general UK population over 65 years of age is 73 per 100,000 person-years.

If patients had ever taken pioglitazone, they were at an 83 percent increased risk of developing bladder cancer, corresponding to a rate of 74 cases per 100,000 person-years. That increased to a rate of 88 cases for those who had taken the drug for at least two years, and 137 cases for patients who had taken a cumulative total of at least 28,000 milligrams of the drug.