The diabetes drug pioglitazone is associated with an increased risk of bladder cancer, according to a Canadian study.
The findings, published in the British Medical Journal, suggest that the risk increases with increasing duration of use and dose.
“Absence of an association with rosiglitazone suggests that the increased risk is drug specific and not a class effect”
However, no increased risk was seen with rosiglitazone, another thiazolidinedione used to help to control blood glucose levels in patients with type 2 diabetes.
Back in 2005, a trial unexpectedly showed an imbalance in the number of bladder cancer cases with pioglitazone compared with placebo. Since then, the association between the use of pioglitazone and bladder cancer has been controversial, with studies reporting contradictory findings.
The current team of researchers assessed whether pioglitazone, when compared with other anti-diabetic drugs, was associated with an increased risk of bladder cancer in type 2 diabetes patients.
They analysed data on 145,806 patients from the UK Clinical Practice Research Database, who were newly treated with diabetes drugs between 2000 and 2013.
Compared with no thiazolidinedione use, the use of pioglitazone was associated with an overall 63% increased risk of bladder cancer – 121 per 100,000 person years versus 89 per 100,000 person years – with the risk increasing with increasing duration of use and dose.
In contrast, the use of rosiglitazone was not associated with an increased risk of bladder cancer in any analysis, suggesting the risk is drug-specific and not a class effect.
The study authors said: “The results of this large population based study indicate that pioglitazone is associated with an increased risk of bladder cancer. The absence of an association with rosiglitazone suggests that the increased risk is drug specific and not a class effect.”
They stressed that, in absolute terms, the risk of bladder cancer remained low. But they suggested clinicians and patients should be aware of the association when assessing the overall risks and benefits of this therapy.
Meanwhile, a second study, also published by the BMJ, compared diabetes drugs – particularly thiazolidinediones and gliptins – in their potential ability to control blood glucose levels and prevent serious complications.
Diabetes drug linked with bladder cancer risk
Professors Julia Hippisley-Cox and Carol Coupland at Nottingham University analysed data on 469,688 adult patients with type 2 diabetes between 2007 and 2015.
They found clinically important differences between different drugs and risk of five key outcomes – blindness, amputation, severe kidney failure, hyperglycaemia and hypoglycaemia events.
Although observational studies, the researchers said the results may have implications for prescribing and that clinicians should be aware when assessing the overall risks and benefits of diabetes drugs.