(RxWiki News) The medications you take need to leave the body somehow, and for some drugs, the kidneys are vulnerable to any side effects since they have such a high level of exposure to the bloodstream.
Apparently, high doses and years of treatment with pioglitazone lead to an slight, but measurable increase in the risk of developing bladder cancer.
"Ask your pharmacist about possible side effects."
In absolute terms, the risks was low – up to 137 extra cases per 100,000 person years. Researchers said that no increased risk of bladder cancer was seen for a similar drug in the same class of diabetic treatments, rosiglitazone, which was also developed by GlaxoSmithKline.
Rosiglitazone has been removed from several countries approval list of pharmaceuticals due to an increased risk of cardiac events while taking the drug.
Early studies on pioglitazone found a link between tumors in the urinary system, and the approval for the drug was suspended, but ultimately the FDA and several countries in Europe allowed pioglitazone to be prescribed.
Both drugs affect the body's sensitivity to insulin, meaning that diabetic patients require fewer injections and lower doses to control their blood glucose levels.
The study analyzed records of 115,727 diabetes patients treated from 1988 to 2009, looking for cases of bladder cancer.
Analysis of risk factors were projected onto control groups to determine the cause, with pioglitazone showing an increase of 83 percent more risk than patients who had not taken the drug.
In raw numbers, the increased risk meant that for 100,000 people during the course of one year, 89 people would develop bladder cancer rather than 73.
Patients at the greatest risk were those who had been under treatment with pioglitazone for the longest amount of time, or had the highest doses. This supports the theory of the kidney processing the drug into a toxic byproduct.
Published alongside the study, Dominique Hillaire-Buys and Jean-Luc Faillie from the Department of Medical Pharmacology and Toxicology in Montpellier, France authored an editorial on the subject, stating,"it can confidently be assumed that pioglitazone increases the risk of bladder cancer. It also seems that this association could have been predicted earlier."
Dr. Hillaire-Buys was referencing the several studies that had raised the question of increased risk for developing bladder cancer when the drug was still awaiting approval. Several of these studies were taken at face value in his native France, where the drug had been banned initially until the European Council overruled the decision.
While no official ruling has been made by the FDA or other agencies, Dr. Hillaire-Buys mentions that,"prescribers who are ultimately responsible for therapeutic choices can legitimately question whether the benefit-risk ratio of pioglitazone is still acceptable for their patients with diabetes."
The study was published in the British Medical Journal on May 31, 2012.
The authors did not make any disclosure of conflict of interest available to the public.