When new safety issues emerge for a drugmaker's top drugs, its finances can take a hit. Amgen's (Nasdaq: AMGN) no exception, as last year's problems around its leading drugs continue into 2008.

Those problems took a toll on the first-quarter results Amgen reported last week. As expected, extra competition and safety issues shrank Amgen's sales of its lead anemia franchise drug; worldwide sales of Epogen and Aranesp took a 20% hit year over year. The lower sales, and the sluggish results for cancer treatment Vectibix after its disappointing clinical trial results last year, drove Amgen's overall quarterly revenue down 2% from the year-ago period.

Amgen's adjusted expenditures didn't help, barely declining from their first-quarter 2007 levels. As a result, operating income growth grew only 1.1%.

Unfortunately for Amgen, its financial results could get worse before they get better. The FDA is set to make decisions later this year on potential label changes for Aranesp that could further affect a sizable chunk of the company's sales. Amgen's other anemia drug, Epogen, might also face continually toughening competition in Europe, and potentially in the U.S.

It's worth pointing out that the falling dollar is providing many U.S.-based drugmakers like Amgen a very nice boost to their top and bottom lines. Both in U.S. and internationally, Amgen's Q1 sales would have fallen by single-digit percentages year over year, but international sales got a hefty 11% boost, thanks to the falling dollar.

Depending whether you're a glass-half-full or half-empty person, you can take it as good news that Amgen reaffirmed its $4.00-to-$4.30 adjusted earnings per share guidance for the year, or bad news that this outlook remains mostly below last year's $4.29 per share.

Other drugmakers, like Pfizer (NYSE: PFE), that are experiencing similar problems with their lead compounds, can't cost-cut their way to sustained long-term financial growth. Until Amgen can get some pipeline and regulatory victories, its lackluster results will likely continue.

Amgen still has a few tricks up its sleeve, including its potential osteoporosis treatment, Denosumab. Its quickest chance to bring a new drug onto the market will arrive later this year, when the FDA issues a likely positive late-July opinion on its thrombocytopenia drug, Nplate. Until then, Fools, keep your fingers crossed.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an approved disclosure policy.