A month after Astrazeneca plc’s $39 billion takeover of Alexion Pharmaceuticals Inc. was finalized, the merged company has hit its first speed bump after the new unit discontinued a phase III rare disease trial. Alexion, of Boston, said it axed the 382-patient CHAMPION-ALS trial of its long-acting C5 complement inhibitor Ultomiris (ravulizumab) in amyotrophic lateral sclerosis (ALS).