Amphastar Pharmaceuticals' stock experienced a significant after-hours plunge of 16.19% following the release of its fourth-quarter financial results, which fell short of analyst expectations across multiple key metrics.

The company reported adjusted earnings per share of $0.73, missing the consensus estimate of $0.92 by 20.82%. This represents a 20.65% decrease compared to earnings of $0.92 per share from the same period last year. Revenue also disappointed at $183.105 million, falling 3.87% below the $190.480 million estimate and marking a 1.83% year-over-year decline.

Other financial metrics showed similar weakness, with adjusted net income of $34.158 million missing the $43.6 million estimate. The across-the-board misses in both earnings and revenue, coupled with year-over-year declines, prompted the sharp sell-off in post-market trading.