The Thousand Oaks, California, biotechnology major earned $2.76 a share in the quarter compared with $2.85 in the year-earlier quarter. Adjusted earnings were $3.81 in the latest quarter.
Revenue advanced 7.1% to $6.63 billion from $6.2 billion.
A survey of analysts by FactSet produced consensus estimates of GAAP earnings of $2.55 a share, or an adjusted $3.36, on revenue of $6.57 billion.
At last check Amgen shares were trading off 1.9% at $236. They finished the regular Tuesday trading session little changed at $240.49.
The profit slip stemmed primarily from the company amortizing costs associated with its November 2019 acquisition of Otezla.
Amgen said it sold more units of pharmaceuticals in the quarter but net selling prices declined.
Product sales were led by sales of Otezla for psoriasis, Mvasi for metastatic colorectal cancer, Kanjinti for breast cancer and metastatic stomach cancer, and Repatha for heart disease, Amgen said.
For full year 2021, Amgen estimated GAAP earnings would range $12.12 to $13.17 a share. It pegged adjusted earnings at $16 to $17 a share.
Amgen expects full-year 2021 revenue to range $25.8 billion to $26.6 billion.
The FactSet survey of analysts for full-year 2021 is estimating GAAP earnings of $14.49 a share, or an adjusted $16.96, on revenue of $26.43 billion.
"We expect continued covid-19 impact and quarter-to-quarter variability throughout 2021, with recovery in the latter part of the year contingent upon the speed and effectiveness of the global vaccine rollout," Amgen said in a statement.
"Recall [that] first-quarter 2020 also benefited from about $100 million in inventory stocking across the portfolio related to covid-19, which we do not expect to repeat in first-quarter 2021."