The number of Medicare Part D drugs being covered by US prescription drug plans (PDPs) varies widely, and an increased share of the cost is being pushed to patients, a new study shows.

As a result, many beneficiaries of Medicare (the US federal health insurance programme for the over-65s and some disabled people) who have serious illnesses such as cancer, multiple sclerosis (MS) and rheumatoid arthritis (RA) could see higher prescription costs next year, warns the study, from Avalere Health, and it suggests that they may need to select PDPs that cover their specific medication needs rather than searching only for the lowest premiums.

The percentage of prescription drugs which will be covered by the top 10 stand-alone PDPs in terms of enrollment for 2012 varies considerably, the analysis shows, with Humana Enhanced covering 79% of Part D-covered drugs but WellCare Classic covering only 47%. The percentage of covered drugs among six of the top 10 PDPs will decrease, although often only slightly, and, overall, a total of 2,306 drugs will appear on at least one formulary next year.

While Humana Enhanced has the highest percentage of drugs covered among the top 10 PDPs, this percentage will decline from 84% of all Part D medications this year to 79% in 2012, says Avalere.

Moreover, the number of plans offering formularies with five or more tiers will continue to increase next year. Nearly 60% of plan offerings will have five or more tiers, up from 41% in 2011 and 30% in 2010 and, at 87%, the overwhelming majority of PDPs will continue to use specialty tiers, which cover high-cost biologic drugs and treatments for diseases such as MS, cancer and RA.

The typical tier structure for five-tier formularies in 2012 is: tier one - preferred generics; tier two - non-preferred generics; tier three - preferred brands; tier four - non-preferred brands; and tier five - specialty/injectible drugs.

Additionally, the use of prior authorisation and quality limits will increase from 2011 to 2012 - from 16.7% to 17.5% and from 15.3% to 17%, respectively, but the use of step therapy will remain low, at 1.6%, the analysis notes.

An earlier study by Avalere Health had found that, on average, premiums are declining for 2012, and coverage options remain very robust as a result of oversight by the Centers for Medicare and Medicaid Services (CMS) and strong competition. 

"While the Part D programme looks quite stable, choice of drugs is increasingly being shifted away from physicians and toward cost-conscious patients," says Avalere chief executive Dan Mendelson. "In assessing Part D plans, Medicare beneficiaries need to look beyond premiums to really understand which drugs are offered, and how much of the cost will actually be covered at the pharmacy counter."

On average, cost-sharing for brand and specialty drug tiers in 2012 will increase in five-tier PDPs; for tier four of five-tier PDPs using one co-insurance tier, there will be an increase of more than $20 from 2011 to 2012 and an increase of over $11 in tier three.

Meantime, average cost-sharing for generic tiers in five-tier formularies will fall in 2012, adds Avalere.