Healthcare costs at large employers are expected to increase by 6 percent next year for the second year in a row, even as high drug costs create new pressures, a new survey found.

The annual survey of large businesses found that even though the cost increases were the same as last year, costs are still running more than twice the rate of inflation, according to the National Business Group on Health, which conducted the poll.

The 6 percent increase for next year is identical to the increase large businesses would have "experienced in each of the past two years had they not made changes to their plan design," the nonprofit group said in a release.

Many employers expect to hold increases to their healthcare plans to 5 percent by making some changes. That is about half the bump for Obamacare plans, expected to be more than 10 percent. Plans sold on the Obamacare marketplaces are for people who do not get their insurance through work.

About 31 percent of employers indicated that high-cost specialty pharmaceuticals that treat conditions such as hepatitis and HIV were the highest driver of healthcare costs. Only 6 percent in 2014 said pharmaceutical costs were the top driver.

Another 80 percent put high-cost drugs as one of the top three highest drivers of healthcare costs. Other drivers included high-cost claimants and treating specific diseases and conditions.

The results come as rates are pouring in for Obamacare plans next year. The healthcare research firm Avalere Health has projected that premiums for silver plans, the mid-tier category of marketplace plans, will increase an average of 11 percent.

Some states have released preliminary Obamacare rates that project increases of up to 50 percent and more, but those final rates could be lower after negotiations with state regulators.

The survey was of 133 large employers from different types of industries.