NEW YORK (CNNMoney.com) - Amgen Inc., the world's biggest biotech developer, beat earnings expectations for the first quarter Tuesday, but analysts were still skeptical about the company's performance.

Amgen, based in Thousand Oaks, Calif., reported a net profit of $1 billion, or 82 cents a share, up 17 percent from $854 million, or 67 cents a share, in the year-earlier period. Sales jumped 14 percent in the first quarter to $3.2 billion.

Amgen (up $1.36 to $70.97, Research) stock dipped 1 percent in after-hours trading to $70.25 per share.

Sales for the biotech's top-selling drug, Epogen, an anemia treatment for dialysis patients with chronic kidney disease, increased 4 percent to $604 million in the first quarter. Sales for the company's No. 2 product, Aranesp, an anemia treatment used in conjunction with chronic kidney disease and chemotherapy, surged 24 percent to $893 million.

But Jennifer Chao, analyst for Deutsche Bank North America, described drug sales as "disappointing," particularly for Neulasta and Neupogen, which increased 13 percent in the first quarter to $896 million, and Enbrel, which increased 11 percent to $658 million. Neulasta and Neupogen are used to fight infections in chemotherapy patients, and Enbrel is a treatment for various types of arthritis.

Les Funtleyder, analyst for Miller Tabak who rates the company a "sell," said he was "underwhelmed" by Amgen's earnings. Funtleyder said he still considers the company to be an overpriced stock, despite the fact that the price has already dropped 11 percent this year.

"Our key issue with them is they they're not a fast-growing company, but they are selling at a fast-growing company's multiple," said Funtleyder.

Biotechs historically outperform Big Pharma on the stock market, but this year the biotech stocks have underperformed pharmaceutical companies and the S&P 500.

To read about first quarter earnings from Genentech, the second-biggest biotech, click here.