A CVS (Photo: M. Spencer Green/AP)

Insurers had to pry customers away from each other to get much Medicare Part D drug plan enrollment growth this year.

Total enrollment in stand-alone Medicare drug plans amounted to 25.5 million in March, up just 1.6% from the total recorded in March 2015, according to analysts at Mark Farrah Associates.

(Related: 3 Medicare Advantage Giants Keep Growing: Mark Farrah)

Enrollment at the 10 biggest issuers grew 1.7%, to 24 million.

Enrollment at all other issuers in the Medicare drug plan market was flat. Those smaller issuers now provide drug coverage for about 1.7 million Medicare enrollees, or about as many Medicare enrollees as they were covering a year ago.

Mark Farrah analysts found that enrollment trends at the 10 biggest Medicare drug plan issuers were also split: Half of the issuers lost enrollees, and half gained enrollees.

EnvisionInsurance Company, the ninth-biggest issuer in the market, managed to boost its 2018 Medicare drug plan enrollment 60%, to 523,019.

CVS Caremark Corp, the biggest issuer, increased its enrollment 11%, to 6.1 million.

No other top 10 issuer increased Medicare drug plan enrollment more than 10%.

CVS has agreed to acquire Aetna Inc. Aetna increased its Medicare drug plan enrollment 4.3%, to 2.2 million.

In March, Mark Farrah reported that Medicare Advantage plan enrollment increased 7.6%, to 21 million.

Mark Farrah analysts note that 18 million Medicare enrollees get drug coverage through Medicare Advantage plans that offer prescription coverage, rather than through stand-alone drug plans.

Mark Farrah has posted a complete version of its Medicare drug plan enrollment report here.

— Read Issuers Post Shocking Individual Health Results: Mark Farrah on ThinkAdvisor.

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