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Only about 18% of dual eligible Medicare recipients have access to all of the most commonly prescribed drugs in the Part D prescription drug benefit plans, according to a new government study.

Exclusions in the new drug plans are limiting drug access to about 82% of the dual eligible population, which is considered the most vulnerable group of people under the new benefit, according to a report released by the Department of Health and Human Services Office of Inspector General. Drug plans under Medicare have more flexibility to limit coverage of drugs, compared to Medicaid.

A total of 30% of dual eligibles are assigned to plans that include less than 85% of the drugs most commonly taken by this group. About half are in plans that cover 85% to 99% of the common drugs. Dual eligibles, who total about 6.4 million, have been assigned to 409 different plans.

Only 178 of the 200 most commonly prescribed medications taken by the dual eligible population are eligible for coverage under the new benefit. The remaining 22 drugs are statutorily excluded. But the dual eligible population will continue to have access to these drugs from state programs in 45 states, the report said.

The OIG report is at www.oig.hhs.gov/oei/reports/oei-05-06-00090.pdf.