Rise of more than 12% was recorded in prescription-drug spending last year in the US, marking the biggest annual increase in over a decade. The figure was revealed by a report by the nation’s largest pharmacy benefit manager.

Specialty medicines played a pivotal role in a record rise in spending in the US last year. Pharmacy benefits manager Express Scripts said new drugs for hepatitis C, and those for inflammatory diseases, multiple sclerosis and cancer significantly contributed to the spending.

Express Scripts, the largest pharmacy benefits manager in the US, has been opposing high drug prices for hepatitis C treatments like Gilead Sciences' Sovadi, which requires a patient to spend $1,000 per day, or $84,000 for a 12-week course of treatment.

An agreement was reached between Express Scripts and Gilead's competitor, AbbVie, in December to include its drug in its largest plan, which caused a decline in Gilead's shares.

Investors were left shocked by Gilead’s announcement for plans to offer discounts of 46% on its hepatitis C drugs, Sovaldi and Harvoni, in 2015.

“For the past several years, annual drug spending increases have been below the annual rate of overall health-care inflation in the US. But that paradigm is shifting dramatically as prices for medications increase at an unprecedented and unsustainable rate”, Glen Stettin, senior vice-president of clinical, research and new solutions at Express Scripts, said in a statement Tuesday.

According to Express Scripts, 743% rise in spending on hepatitis C drugs, driven primarily by Gilead's medicines, was witnessed last year. Going by the forecast of Express Scripts, there would be a rise of 67% in spending on that category this year due to pricing control strategies, like the one it employed with AbbVie.