A bipartisan group of U.S. senators announced legislation yesterday to reimburse states for the cost of backup pharmacy systems that are helping Medicaid patients who can't access their new Medicare prescription drug benefits.

The bill would require the federal government to reimburse states for the cost of prescriptions for low-income seniors and people with disabilities who were eligible for coverage under Medicare Part D as of Jan. 1. Thousands of these Medicaid patients are struggling to fill prescriptions due to a variety of glitches related to the transition.

But Sen. Chuck Grassley, R-Iowa, the chairman of the Senate Finance Committee, said yesterday that the rush to legislate was premature.

Echoing assurances from the Center for Medicare and Medicaid Services, Mr. Grassley said that states will be reimbursed by the private health plans that have been paid by the government to provide the medications.

State officials are concerned, however, because health plans won't reimburse Medicaid programs for 100 percent of their costs. That's because health plans can buy medications more cheaply than the states can, and are only being required by the federal government to pass along to states what they would have paid.

Pennsylvania officials estimated this week that about 10 percent of the money the state is spending on emergency prescriptions could be at risk because of the reimbursement issue. David Parrella, vice chair of the National Association of State Medicaid Directors, said the share of money at risk in some states could be even greater.

States have logistical concerns, too, since Medicaid programs could be trying to collect money from as many as 20 companies that could be providing Part D benefits to Medicaid recipients in a given state.

"They've basically told us we're going to get reimbursed by the plans," said Mr. Parrella. "But we have no contract with the plans, [the federal government] does. So, what's their incentive to be prompt and cooperative with us?"

The bill, which was introduced by Sens. Frank Lautenberg, D-N.J., and Olympia Snowe, R-Maine, would reimburse states through an equivalent reduction in funds owed by each state under the "claw back" provision of the new Medicare law. The law required the federal government to collect money from states in exchange for Medicare providing drugs to Medicaid patients.