Editor’s note: This article was updated at 8:35 a.m. on April 28 with up-to-date information on Amgen’s stock price.

Amgen’s shares fell nearly 8% following the company’s April 27 release of its first quarter 2021 earnings, which saw a decline in both revenue and net income compared to a year earlier.

Amgen is headquartered in Thousand Oaks and is one of the largest biotech firms in the world. Its revenue in the first quarter of 2021 was $5.9 billion, down from $6.1 billion in the first quarter of 2020.  Net income fell more than 10%, from $1.8 billion in the first quarter of 2020 to $1.6 billion in the first quarter of 2021.

As a result, non-adjusted earnings per share declined about 8%, from $3.07 to $2.83.

Zacks Consensus Estimate had predicted revenue of about $6 billion as well as an adjusted earnings per share of $4.  Amgen’s adjusted earnings per share came in below that estimate, at $3.70.

Amgen’s stock closed at $255.13 on April 27 and then dropped to $246 in after-hours trading after the earnings were announced. It opened at $241.52 the next morning and was trading at around $235 a few hours later.

The drop in revenue and earnings could be attributed to lower net selling prices that were partially offset by growth in volume, the company said.

“As we entered 2021, we knew that COVID would likely introduce some variability,” Amgen CFO Peter Griffith said during the company’s earnings call. “And as the quarter progressed and we saw a continuing cumulative effect of COVID cases on prescribing patterns, we anticipated that Q1 would be more negatively impacted.”

Amgen’s full year revenue guidance is still at $25.8 to $26.6 billion, but the company has revised its non-adjusted earnings per share guidance downward, to between $9.11 and $10.71.

“While we expect to see improvements in the rate of recovery, that recovery will be more heavily weighted in the second half of the year,” Griffith said.

Total product sales saw a 5% decline in the first quarter of 2021 despite a 4% growth in unit volumes, due to a 7% drop in net selling price.

One of Amgen’s most successful drugs, Enbrel, which treats several chronic inflammatory conditions such as rheumatoid arthritis, saw a steep decline, dropping 20% year-over-year, to $924 million in sales.

Otezla, which Amgen acquired in 2020 and which also treats chronic inflammatory conditions, saw sales dip 1% year-over-year, falling to $476 million in the first quarter of 2021.

“Otezla remains the market leading branded systemic medication for psoriasis, with an approximately 30% share of first line treatment,” Griffith said. “However, new-to-brand prescription volume remains flat as COVID-19 continued to suppress the diagnosis and treatment of psoriasis patients.”

Griffith said Otezla remains a top priority for the company, however, adding that “geographic expansion” will help its growth in the future.

Sales of Repatha, which is used to treat high cholesterol, was up 25% in the first quarter of 2021, driven by a 36% growth in volume, totaling $276 million.

Prolia, a drug used to treat osteoporosis, was up 16% year-over-year, with sales of $758 million, driven by 13% volume growth.

Aimovig, a migraine prevention drug, was down 7% in the quarter, but Griffith said the drug remains a leader in the market.

“Given the head-to-head data we’ve generated showing Aimovig superiority against Topiramate, we’re confident we can help many more patients suffering from chronic migraine,” Griffith said.

Amgen generated $1.9 billion of free cash flow in the first quarter versus $2 billion in the first quarter of 2020.

“While our business continued to be impacted by the COVID-19 pandemic particularly in the first two months of the quarter, we are encouraged by strong volume trends in many of our newer products and remain confident in the outlook for the full year,” Amgen CEO Robert A. Bradway said in a company news release.