Surmodics (SRDX) said late Thursday it disagrees with the US Federal Trade Commission's decision to challenge the company's proposed acquisition by private-equity firm GTCR, which owns a stake in medical coatings maker Biocoat.

The antitrust regulator has sued to block the deal alleging that it's anticompetitive.

The proposed merger would result in "a highly concentrated market for outsourced hydrophilic coatings and eliminate significant head-to-head competition" between Surmodics and Biocoat, the FTC said Thursday.

Surmodics said it was disappointed by the FTC's decision to begin litigation, adding that the deal was "pro-competitive."

"Surmodics intends to vigorously defend this case in court in order to complete the merger," the company said.

Surmodics shares were down 4.8% in recent premarket activity Friday.