Medicare patients choosing low-cost drug plans, analysis finds

"The shift of enrollees to low-cost plans validates that market competition works, as enrollees are rewarding sponsors with innovative packages that offer an attractive monthly premium," said Avalere senior vice president Bonnie Washington in a statement.

The analysis noted that low-cost options, such as the new AARP Saver Plus plan, have seen spikes in enrollment. Despite its recent entry to the market, the AARP plan now ranks ninth among PDPs, Avalere said.

Overall, the firm projected stable costs for Medicare Part D premiums, which rose by about two percent between 2012 and 2013.

—This post was changed at 1:52 p.m. to reflect that the AARP Saver Plus plan ranks ninth, not 10th, among PDPs.