Commission pursued merger challenge to halt pharma practices it believes can stifle competition and keep drug prices high. Other large biopharma transactions may face similar challenges as FTC pursues its new merger program.

The commission seeks a preliminary injunction by 31 October to block the closing of the proposed Amgen-Horizon merger. Harvard Professor Aaron Kesselheim, FTC’s expert, says Amgen could circumvent a commitment not to bundle its and Horizon's products. The Pfizer-Seagen merger agreement also gets a second request for information.

The US firm’s potential rival to Horizon’s Tepezza, VRDN-001, showed positive signals in a small group of patients with chronic thyroid eye disease in a Phase I/II trial, but its decision to drop one planned dosing regimen from an upcoming pivotal trial has put off some analysts.

The US Federal Trade Commission is taking a stand against rebating and bundling practices pharma companies use in negotiations with payers as it seeks to block Amgen’s $28bn acquisition of Horizon.