Changes in drug utilization for seniors without prior prescription drug insurance.

(1) After the passage of the Medicare Modernization Act, a majority of individuals without previous prescription drug coverage obtained coverage under Medicare Part D. (2) Among previously uninsured seniors, utilization of prescription drugs increased with the introduction of Medicare Part D. There was rapid uptake of newly marketed generics. (3) Dual eligibles had little change in prescription utilization or rates of switching between drugs after the implementation of Part D. Out-of-pocket spending was significantly reduced for this population.