A key U.S. senator sent letters to all 50 states this week asking how they sanction doctors in their state health programs and whether they alert the federal government when they do.

In his letters, Sen. Charles Grassley, R-Iowa, cited examples from a ProPublica report last month that found doctors who had been kicked out of state Medicaid programs for the poor were able to continue prescribing drugs to elderly and disabled patients in Medicare.

In 2005, for example, Florida booted Dr. Enrique Casuso from its Medicaid network using a provision that allows it to end contracts without cause on 30 days' notice. A memo justifying his removal said Casuso was seeing up to 81 Medicaid patients a day in addition to his non-Medicaid cases. Investigators found cases in which he lacked "awareness or oversight of the medication prescribed."

A copy of Casuso's termination letter was sent to Medicare. But Casuso continues to prescribe in Medicare's drug program, known as Part D, ProPublica reported.

In 2010, he prescribed more antipsychotics to elderly patients – 8,900, including refills dispensed – than any other doctor in the country. Many of those went to patients with dementia even though warnings from the Food and Drug Administration say the drugs increase the risk of death in such patients.

Casuso defended his prescribing, telling ProPublica the drugs were necessary to keep his patients safe and to calm them.

Physicians can be terminated from Medicaid for a variety of reasons. If they are terminated with cause, the state must prove misconduct. A termination without cause doesn't require any burden of proof. It may be because a doctor has stopped seeing Medicaid patients or because it is a quicker way of severing ties with a doctor suspected of wrongdoing.

The concern, Grassley wrote, is that while states use "without cause" terminations to quickly remove doctors from their Medicaid networks, the actions are not considered disciplinary and can't be used against doctors by Medicare. Terminations with cause, which are formal sanctions, can take much longer because they can be appealed.

"States' current practice of without cause termination from Medicaid may speed their ability to protect Medicaid patients, but it can expose Medicare recipients to potentially unsafe medical treatment and keeps tax dollars flowing to unworthy providers," wrote Grassley, the ranking Republican on the Senate Judiciary Committee.

Medicaid is jointly funded by states and the federal government, but is run by the states. Medicare is run by the federal government.

Grassley asked each state Medicaid program to indicate how it determines when to use the "without cause" provision and how it informs Medicare of its actions, if at all. Once states respond, Grassley plans to ask Medicare whether and how it acts on this information.

Physicians can continue to prescribe in Medicare unless they have been formally excluded from the program.

This is not the first time Grassley has questioned how Medicaid monitors prescribing by physicians and others. In 2010, he sent letters to all states asking for the names of the top prescribers of painkillers, antianxiety drugs and antipsychotics in their Medicaid programs. He followed up last year to ask whether the states had cracked down on those who wrote large numbers of prescriptions.

The senator also has focused on doctors' ties to drug companies. He was a key proponent of the Physician Payment Sunshine Act, which requires all drug and medical device makers to make public their payments to doctors beginning next year. And in 2009, he sent letters to prominent medical organizations seeking details about their industry financial support.

Justin Senior, the deputy secretary of Florida's Agency for Health Care Administration, said earlier this year that the ability to terminate a doctor's Medicaid contract without cause is "a tool that we can use when we see someone we feel might be doing something that is inappropriate."

In Florida, if physicians are expelled for cause from Medicaid, they cannot renew their state medical licenses. This can make the legal battle over such a termination much fiercer.

But Senior said that the physicians who are removed without cause have no blemish on their record. "They still have a license to practice medicine," he said. "They can happily make a living billing Medicare, Blue Cross ... billing whoever is willing to do business them."

Medicare could use these cases as tips to pass onto its own fraud investigators.

In his letter, Grassley cited two other examples from ProPublica's report:

Chicago psychiatrist Michael Reinstein wrote an average of 20,000 prescriptions for the antipsychotic clozapine in Part D each year between 2007 and 2009, and another 14,000 in 2010. Last year, he was suspended from Illinois Medicaid, and the Department of Justice has sued him for fraud. But he remains able to provide services under Medicare. Reinstein has treated patients at more than 30 Chicago-area nursing homes and long-term care facilities. He has defended his prescribing in media interviews.

Miami psychiatrist Fernando Mendez-Villamil was terminated without cause from Florida Medicaid in 2010 amid questions about his prescribing of mental health drugs. The Florida medical board also has accused him of giving patients as young as 3 a variety of such drugs without properly diagnosing or monitoring them. He remains eligible to prescribe in Medicare. His lawyer has said his client had done nothing wrong.

The Centers for Medicare and Medicaid Services, which oversees both programs, did not respond to a request for comment. Officials have previously declined to comment on the physicians named in this story.

In a statement, Grassley said he wants to "get first-hand information" to make sure actions taken by Medicaid programs don't leave Medicare patients at risk.