According to a report from the IMS Institute for Healthcare Informatics , Americans spent more money on drugs than they ever have before with spending jumping by 13% to $374 billion, driven by innovative but expensive new drugs designed to treat Hepatitis C.

The new hepatitis C drugs accounted for more than $11 billion of the spending with the influx of millions of people newly insured under the Affordable Care Act was less of a factor than originally expected accounting for only $1 billion.

"This was an outstanding year, really a once-in-a-lifetime year," said Michael Kleinrock, director of research development for IMS Health. "It was the largest dollar growth in a single year we've ever measured. This is a huge amount of extra spending."

The bulk of the spending was from people seeking breakthrough new treatments for Hepatitis C. This new treatment promised a cure but came at a hefty price tag of more than $80,000 per patient.

"Harvoni and Sovaldi offer a cure at a price that reduces hepatitis C treatment costs now and will deliver significant savings to the healthcare system over the long term," Gilead Sciences spokeswoman Cara Miller said. "We believe the prices of Harvoni and Sovaldi reflect the value of the medicines."

New drugs contributed $20.3 billion to prescription drug spending with Multiple sclerosis spending rising 24.4% to $13.9 billion last year, driven by $4.7 billion in new brands and oral therapies.

The steep increase in U.S. prescription drug spending is unlikely to be repeated this year, Kleinrock said.

Competition has already forced Gilead Sciences to lower prices on their new hepatitis C drugs, and they are likely to fall even more and even new treatments are released on the market.

Last year was unusual because many hepatitis C patients had avoided treatment, waiting for the rollout of Gilead's new drugs, said Robyn Karnauskas, a biotech analyst at Deutsche Bank. This created a massive pool of patients eager to begin treatment for the liver-damaging virus.

"The therapies were really poor before Gilead's," she said. "All of a sudden doctors felt comfortable treating these patients, so you saw this explosion of demand."

"We project relatively flat sales for the next few years, not really growing," Nadeau said. "Last year was the big year, and from here on out it's going to be relatively consistent."

Nadeau said competition from other hepatitis C drugs will drive the pricing of Gilead Sciences' drugs down to about $50,000 or less.

That's one reason Kleinrock believes that prescription drug spending won't rise as much as it did in 2014. "We do think 2014 is a bit of a one-off and we will see growth come down," he said. "But it may be too early to tell."