Amgen (NASDAQ:AMGN) shares got smacked around a bit at the end of Thursday's trading session, but it appears some reactionary investors hit the panic button too soon. The company missed analysts' expectations by a few pennies, but its fourth-quarter earnings showed an impressive increase in the revenues brought in by its drugs.

Part of the reason for the knee-jerk reaction -- resulting in the stock's 2% fall Thursday -- was an apparently inadvertent posting of earnings to the company's website, prior to the release of the press announcement and market close.

Amgen's quarterly earnings increased 20%, to $545.9 million, or $0.41 per share, from $456.4 million, or $0.34 a share, in the same quarter last year. Excluding charges and gains, earnings were $0.46 a share, compared to $0.35 a share, $0.02 shy of analysts' expectations. The miss was attributed to increased expenses -- mostly related to increased sales.

In its conference call (courtesy of CCBN StreetEvents), Amgen pointed to 58% product sales growth for the year. While a great showing in 2003 might cause some tough comparisons for 2004, Amgen has several possible revenue drivers up its sleeve.

First, Amgen hopes to gain FDA approval to market what is currently its rheumatoid arthritis drug Enbrel to psoriasis sufferers, a green light it hopes will blink this year. The company believes that 1 million people suffer from a moderate to severe form of the disease.

There's also cinacalcet, a drug for kidney disease that has shown promise, which Amgen hopes to have approved within the first half of 2004. If it gets the regulatory agency's OK, it will be the first medication in a new class of drugs, which could gear into quite an exciting revenue opportunity for the company.

The drug maker's been revving its engines for additional growth for quite some time, as discussed by fellow Fool Rick Munarriz last month, giving investors an exciting story to watch unfold. Today, its shares have risen 1%, as investors digested the news. Amgen may have delivered a "miss" last night, but when it comes to stacking up sales of its drugs, it's been hitting on all cylinders.

Talk over this company's outlook with other Fools on the Amgen discussion board.

Alyce Lomax welcomes your feedback via e-mail.