horizon therapeutics tumbled in premarket trading tuesday following a published report that us regulators will move to block the 278 billion acquisition of the drugmaker by amgen bloomberg citing a person familiar with the matter late monday reported that the federal trade commission is expected to file a lawsuit tuesday to block the deal on the grounds it would hamper innovation and slow the pace of drug development amgen in december said it would pay 11650 a share in cash for horizon marking the largest healthcare merger announced in 2022 amgen said it wasnt aware of any ftc decision on the deal while horizon deferred comment to amgen according to the bloomberg report horizon shares which closed monday at 11225 were recently down nearly 17 at 9349 in premarket trading while amgen shares edged up 06 to 235