Zeinab Atwi, 16, left, and John Kidd, 12, receive dialysis treatment July 18 at DaVita Flint Dialysis Center in Flint, Mich.(Jake May/The Flint Journal via AP)

The government warning seemed scary enough.

In March 2007, the Food and Drug Administration issued a stern “black box” warning regarding the anemia drugs commonly prescribed to dialysis patients: The popular drugs, known as ESAs, could increase the risk of heart attacks, stroke, blood clots and death.

But according to a new paper by researchers who studied the use of the drugs for months before and after the warning, the FDA’s black box “did not appear to influence ESA prescribing among the overall dialysis population.” Instead, the use of the drugs continued a slow, steady decline rather than taking a sharp drop, according to the paper.

“Regrettably, the dialysis centers treating patients didn’t appear to be paying a lot of attention to the black-box warning — and they should,” said Dennis Cotter, one of the authors of the paper appearing in the journal BMC Nephrology.

What seems to have curtailed use of the drugs more than the FDA warning was a change in the Medicare payment.

Before 2011, the larger the dose, the more a facility profited. At one point, the drugs were among the bestsellers in the Medicare system.

In 2011, however, Medicare eliminated the financial incentive for higher doses, setting a fee for a bundle of dialysis services and drugs. This way, hospitals and clinics make more money if they use the drugs more frugally.

To guard against providers using too little, Medicare requires that patients’ condition be monitored.

Without the incentive to use more, the use of ESAs fell about 30 percent from projected levels in 2011.

“Clearly, the providers are paying more attention to payment,” Cotter said.

DaVita and Fresenius Medical Care, two of the largest dialysis providers in the United States, have said that their dosing decisions are based on the health of the patient and that they take into account the federal government’s findings.

They disputed the findings in the report.

“All credible analysis shows that the [FDA] label change resulted in a significant drop in ESA use for patients on dialysis,” according to a statement from DaVita officials.

The DaVita officials said the reason the drop in usage did not come precipitously when the label changed was that doctors had already begun curtailing its use.

Moreover, they said, while the drop in use in 2011 may have been due in part to the payment change, most of the reduction came because of even sterner FDA warnings that year.

“Our approach to anemia management has consistently focused on determining ESA usage and dosing protocols on an individual patient basis,” according to a statement from Frank Maddux, Fresenius’s chief medical officer and executive vice president for clinical and scientific affairs. “The goal is to avoid both low and high extremes in a patient’s hemoglobin to match the scientific understanding and regulatory guidance in use of ESA medications.”