The number of physicians who each prescribed more than $5 million worth of prescriptions increased more than tenfold, from 41 in 2011 to 514 in 2015, according to federal data obtained by ProPublica.
The number of prescribers exceeding $10 million in drug costs soared from two to 70 over the same time period, the data show. Prescribers are mostly physicians but also include some nurse practitioners.
The increased spending was largely driven by prescriptions for Harvoni or Sovaldi, new, expensive drugs that treat hepatitis C. Other expensive drugs accounting for the rise in spending on prescriptions include those that treat cancer, multiple sclerosis and rheumatoid arthritis.
Medicare Part D, the federal drug program that covers more than 41 million seniors and disabled people, in 2015 accounted for $137.4 billion in drug spending before rebates from drug companies were factored in. In 2014, Medicare Part D spent $121.5 billion.
"The trends in this space are troubling and don't show any signs of abating," said Tim Gronniger, deputy chief of staff at CMS, according to the report. "It's going to be a pressure point for patients and the program for the foreseeable future."