Amphastar Pharmaceuticals posted fourth-quarter revenue of $183.1 million, down 1.8% year-on-year, missing consensus estimates. Adjusted EPS fell to $0.73 from $0.92 a year ago, while operating margin narrowed to 19.4% from 24.2%, highlighting rising costs relative to sales.

Shares plunged 15.8% in the afternoon session as investors reacted to the earnings and profitability shortfalls. This sell-off underscores concerns over slowing growth trends and margin pressures at the company.