The nation's largest pharmacy benefits manager says prescription drugs spending rose 13 percent last year, the largest annual increase since 2003.
Express Scripts says the gains were fueled by pricey specialty drugs that accounted for about 31 cents of every dollar spent on prescriptions even though they represented only 1 percent of all U.S. prescriptions filled.
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Specialty drugs are advanced medications that treat complex or chronic conditions like hepatitis C and multiple sclerosis.
Express Scripts Holding Co. and several insurers have warned for more than a year about the growing financial impact from specialty drugs like Gilead Sciences' hepatitis C treatment Sovaldi.
Express Scripts also says in an annual report on prescription spending that the specialty drug trend will slow to more sustainable levels over the next three years.