One of the nation’s largest providers of kidney dialysis deliberately wasted medicine in order to reap hundreds of millions of dollars in extra payments from Medicare, a former clinic nurse and a doctor are charging in a whistle-blower lawsuit.

The lawsuit says that the company, DaVita, used larger than necessary vials of medicine knowing that Medicare would pay for the unused portion of each vial if it were deemed unavoidable waste. DaVita, which treats nearly a third of the nation’s dialysis patients, denies the accusations.

The accusations are the latest related to how financial incentives may have driven overuse of pharmaceuticals in the dialysis business. In January, Medicare began a payment system that pays for the overall treatment and does not pay separately for the drugs accompanying it. Many practices, including the size of some vials used, suddenly changed, providing an instant case study of how financial incentives can influence treatment choices.

The lawsuit says that until January, for example, DaVita required nurses to use one 10-microgram vial of Zemplar, a vitamin D drug, instead of a six-microgram dose in three two-microgram vials,. It then billed Medicare for all 10 micrograms even though four went unused.