Amgen ( AMGN) and Immunex ( IMNX) are engaged, but the wedding is still a few months off, so Wednesday, each firm reported separate fourth-quarter earnings that offered mixed results and narrowly missed Wall Street estimates.

Amgen, which will acquire Immunex in a $16 billion deal announced in December, said fourth-quarter net income fell 15% to $163 million, or 15 cents per share, compared to net income of $210 million, or 19 cents per share in the year-ago quarter.The drop in earnings was the result of a one-time charge totaling $243 million, or 15 cents per share, related to the termination of partnerships with other drug companies, the company said.Excluding the charge, Amgen's posted fourth-quarter earnings of 30 cents per share, one cent shy of analysts' expectations, according to Thomson Financial/First Call.

Fourth-quarter revenue totaled $1.12 billion, an 18% increase from the year-ago quarter.

Immunex said fourth-quarter net income totaled $41.6 million, or 7 cents per share, compared to net income of $49.2 million, or 9 cents per share, in the fourth quarter last year. Revenue in the quarter rose 10% to $277 million.

Immunex missed analysts' earnings estimates for the fourth quarter by one cent, but the company said results were hurt by costs related to the Amgen merger. Excluding those costs, the company said earnings totaled 8 cents per share.

Strong sales of blockbuster drugs bolstered each company's bottom line.

Over at Amgen, combined sales of Epogen, the company's anemia-fighter, jumped 7% to $572 million in the fourth quarter, compared to last year. Analysts were looking for Epogen sales of around $550 million in the quarter.

Sales of Neupogen, used to fight infection in chemotherapy patients, reached $353 million in the quarter, compared to sales of $311 million last year. Analysts were expecting Neupogen sales of about $345 million.

The fourth quarter was the first full reporting period for Aranesp, Amgen's second-generation anemia drug. Sales totaled $37 million in the quarter, which fell below the light end of expectations, which ranged from $40 million to $80 million.

At Immunex, nearly all of the focus is on sales of Enbrel, the company's rheumatoid arthritis drug. Enbrel sales in the fourth quarter totaled $216.3 million, above analyst expectations of around $211 million.

Shares of Amgen jumped $2.40, or 4%, to $58.46 per share in Wednesday trading, spurred along by a Merrill Lynch upgrade to strong buy. Immunex shares rose $1.35,

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