In his latest volley, a letter sent Wednesday to Kathleen Sebelius, secretary for the U.S. Department of Health and Human Services, Grassley demanded exact answers to three pointed questions about what her department is doing to address the problem.

``The federal government has an obligation to figure out what's going on here,'' Grassley said in a statement e-mailed to The Miami Herald Wednesday. ``The taxpayers are footing the bill, and Medicare and Medicaid are already strained to the limit. These programs can't spare a dollar for prescription drugs that aren't properly prescribed. The conclusion might be that there isn't any fraud, but it's important to reach a conclusion one way or the other and fix whatever is broken.''

In the Sebelius letter, Grassley said his concern was triggered by a ``Florida provider who wrote 96,685 prescriptions for mental health drugs in a 21-month period.'' The letter did not identify the provider, but state records confirm that it is Fernando Mendez-Villamil, a psychiatrist with an office on Coral Way.

State Medicaid records independently obtained by The Herald show that over a two-year period Mendez-Villamil wrote almost twice as many prescriptions for mental health drugs as the No. 2 Medicaid prescriber in the state.

Robert N. Pelier, attorney for Mendez-Villamil, said Wednesday he and his client learned about the letter only after receiving a call from The Miami Herald. He said the psychiatrist tried to reach Grassley's office when his prescription numbers were made public to give the proper context to the doctor's prescription patterns and ``why he is an intricate part in the community.'' Pelier said he had not received a response from Grassley.

``What my client believes is that he's been a victim of this healthcare debate,'' the attorney said. ``The majority of his prescriptions are expensive because they're cutting-edge pharmaceuticals.''

Pelier said Mendez-Villamil has been recently terminated from the Medicaid program and is now seeing some patients for free. ``We are pursuing legal action against AHCA [Agency for Health Care Administration] for the improper termination of doctor Mendez-Villamil from Medicaid,'' he said. The suit was filed in July.

Meanwhile Ryan Wiggins, spokesman for the Florida Office of the Attorney General, confirmed there is an ongoing investigation into Mendez-Villamil that involves ``complicated issues of medical necessity. . . . We cannot comment further at this time.''

Last December, Grassley's office calculated Mendez-Villamil's numbers meant ``this physician wrote approximately 153 prescriptions each and every day, assuming he did not take vacations.''

Earlier this year, Mendez-Villamil told The Herald that he works long hours and often gives each patient four or five prescriptions, accounting for the large numbers.

In April, Grassley wrote to all state Medicaid agencies requesting data about certain mental health drugs. On Wednesday, Grassley's office said the Florida provider identified by The Herald as Mendez-Villamil had the second-highest number of prescriptions in the nation for the generic form of Xanax in the data they analyzed.

The Wednesday letter also noted that the top Zyprexa provider in Florida wrote 1,356 prescriptions for 309 individuals in 2008 and 1,238 for 236 in 2009. The Herald independently verified from state data that this provider was Mendez-Villamil, and he wrote more than twice as many Zyprexa prescriptions as the No. 2 provider in the state.

``I want to be clear that none of the information provided suggests any illegal or wrongful behavior,'' Grassley wrote. But such huge numbers ``might also suggest overutilization or even healthcare fraud. The only way to determine veracity is through appropriate oversight by [Health and Human Services] and continued monitoring by the Congress and the [Senate Finance] committee.''