Premiums for Medicare's Part D prescription drug program are expected to slightly decline in 2018, the first drop in five years, the Trump administration said Wednesday.

The monthly Part D premium is projected to be $33.50 per month in 2018, down from $34.70 this year, according to the Centers for Medicare and Medicaid Services.

The decline is the first in five years for average Part D premiums, the administration said.

"This is encouraging news for the nearly 43 million seniors who are enrolled in the program," said Health and Human Services Secretary Tom Price.

The projected decline is based on bids submitted by drug plans for basic coverage in Part D.

The decline comes despite surging spending in Medicare on specialty drugs, a trend that is also driving up overall Medicare costs.

A 2017 Medicare Trustees report found that growth in Medicare spending on prescription drugs exceeds growth in other Medicare spending and overall U.S. healthcare spending.