A Senate committee chairman said he is concerned about the “serious vulnerabilities” detailed in a ProPublica report about scams that target Medicare’s popular prescription drug program.

Sen. Tom Carper, D-Del., who chairs the Homeland Security and Governmental Affairs Committee, said in a statement that he plans to ask Medicare officials and the inspector general of the U.S. Department of Health and Human Services “to look into the specifics of these cases, as well as determine the extent of any program-wide vulnerabilities that may have allowed them to occur.” The committee monitors fraud in government programs.

ProPublica reporters, using Medicare’s own data, identified scores of doctors whose prescription patterns within the program bore the hallmarks of fraud. The cost of their prescribing spiked dramatically from one year to the next — in some cases by millions of dollars — as they chose brand-name drugs that scammers can easily resell.

The cost of medications prescribed by one Miami doctor jumped from $282,000 to $4 million in one year, but her lawyer said Medicare never questioned it. A Los Angeles psychiatrist said Medicare didn’t shut off his provider identification number, used to fill prescriptions, even though he claimed someone had forged his name on more than $7 million worth of them.

All told, just the schemes identified by ProPublica totaled tens of millions of dollars.

While credit card companies routinely flag or block suspicious charges as they happen, the detection system used by Medicare’s massive drug program sometimes allows years to pass before taking action that might stop the fraud.

Known as Part D, the program provides coverage to 36 million seniors and disabled people. It cost taxpayers $62 billion last year.

ProPublica has spent the past year examining Medicare’s oversight of Part D. It found that Medicare doesn’t analyze its prescribing data to root out doctors whose inappropriate drug choices endanger patients. Nor has it flagged those whose unchecked devotion to name-brand drugs, instead of generics, adds billions in needless expense.

ProPublica also noted how doctors who had been terminated from state Medicaid programs for questionable prescribing patterns have continued to give patients large quantities of those same drugs through Part D.

Spurred by that report, Sen. Charles Grassley, R-Iowa, the ranking Republican on the Senate Judiciary Committee, sent a letter Friday to Marilyn Tavenner, administrator of the Centers for Medicare and Medicaid Services, asking what the agency is doing about such doctors.

Several months ago, Grassley asked each state Medicaid program to explain its process for terminating doctors and notifying Medicare once it does so. In his letter to Tavenner, Grassley said he is particularly concerned that doctors can be terminated “without cause” from Medicaid and remain in good standing with Medicare.

He cited three doctors identified by ProPublica who had been suspended or terminated from Medicaid but remained large prescribers in Part D.

This practice by states, he wrote, “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,” he wrote.

Grassley found that states varied widely in how they terminated providers in Medicaid. He asked Tavenner to explain how her agency keeps track of such providers.

Jonathan Blum, principal deputy administrator of CMS, said in a statement that his agency takes fraud in Part D seriously and is committed to making improvements. "We look forward to working with Congress and the HHS Inspector General to continue to protect beneficiaries and taxpayers from Medicare fraud, waste and abuse," he wrote.