THURSDAY, June 16 (HealthDay News) -- The U.S. Food and Drug Administration is warning consumers that the popular diabetes drug Actos (pioglitazone) may increase the risk of bladder cancer when used for more than a year.

The agency's warning comes five days after Germany and France pulled Actos from the market, citing similar concerns. Actos is in a class of drugs called thiazolidinediones, the only other member of which, Avandia (rosiglitazone), was taken off U.S. pharmacy shelves in May because it was linked to an increased risk of heart attacks.

The new cancer warning will appear on the labeling, the FDA said.

However, although Actos does have some side effects, "the beneficial effects of Actos, I think, outweigh any possible risk of cancer," said Dr. Joseph Giangola, medical director of diabetes at Hackensack University Medical Center in Hackensack, N.J.

Actos is used to control blood sugar and is sold alone or in combination with metformin (Actoplus Met, Actoplus Met XR) and glimepiride (Duetact). In 2010, more than 2 million patients were taking these drugs, according to the FDA.

The new warning is based on FDA's review of data from an ongoing study, which found that Actos increased the risk of bladder cancer among patients taking the drug over a long period at the highest doses.

In one study involving more than 193,000 patients with diabetes, patients taking Actos were on the drug for an average of two years, the FDA said. "Compared to never being exposed to pioglitazone, a duration of pioglitazone therapy longer than 12 months was associated with a 40 percent increase in risk [for bladder cancer]," the agency said.

In addition, the agency says it is aware of the French study that caused France to pull the drug. That study showed a dose-response effect, where risks for bladder cancer rose as time spent taking Actos lengthened past one year.

Right now, the FDA is advising doctors not to use Actos in patients with bladder cancer and to use it with caution in patients who have had bladder cancer. In addition, the agency says that "the benefits of blood sugar control with pioglitazone should be weighed against the unknown risks for cancer recurrence."

The agency said diabetes patients should also tell their doctor if they are having symptoms of bladder cancer such as blood or red color in urine, an urgent need to urinate or pain while urinating and pain in back or lower abdomen.

In addition, patients should talk to their doctor about any concerns they have about Actos, the FDA noted.

For his part, Giangola said he is cautious when prescribing Actos. "We try to select the most insulin-resistant people to give Actos to," he said. "Those people do well with Actos."

But if Actos was taken off the market, there would be nothing to replace it, Giangola said. With Avandia essentially gone, "there is no medicine that directly influences insulin resistance the way Actos does," he said.

Giangola added that patients should not be overly concerned right now. "To jump now when we have only one medication in this class would be rash," he said. "They really ought to wait until there is more definitive evidence."

"What's worse -- the theoretical risk [of cancer] or the well-known risk of letting your blood sugar remain high? I say it's clearly [the risk of] letting your blood sugar run higher," Giangola said.

In a statement, Takeda Pharmaceuticals North America Inc., the maker of Actos, said it remains positive about the drug.

The company said in a statement that it is "confident in the therapeutic benefits of Actos and its importance as a treatment for type 2 diabetes. The company remains committed to Actos and Actos-containing medications, and to the millions of people living with the disease."

More information

For more information on diabetes, visit the U.S. National Library of Medicine.