Total enrollment in stand-alone Medicare Part D prescription drug plans (PDPs) rose 4.5% between 2010 and 2011, to more than 18 million.

But stand-alone PDPs now account for about 63% of the Medicare enrollees with Part D drug coverage, down from 66% in 2010, according to Avalere Health L.L.C., Washington.

PDPs and other plans run by units of UnitedHealth Group Inc., Minnetonka, Minn. (NYSE:UNH), Humana Inc., Louisville, Ky. (NYSE:HUM), and Universal American Corp., Rye Brook, N.Y. (NYSE:UAM)., are handling about 43% of the Part D market this year, up slightly from 42% of the market in 2010.

Avalere also is reporting that local preferred provider organization (PPO) Medicare Advantage plans seem to be gaining in terms of Medicare Advantage market share as new provider network rules cause a sharp drop in Medicare Advantage private fee-for-service plan enrollment.

- Allison Bell