Merck & Co.'s (MRK) first-quarter net income fell 56% on restructuring and merger-related costs and a year-ago payment from an AstraZeneca PLC (AZN) partnership.

The company also cut its 2009 revenue estimate to $23.2 billion to $23.7 billion from $23.7 billion to $23.95 billion while reiterating its profit target.

Shares fell 2.8% premarket to $24.51 as the quarter's results missed analysts' expectations.

Expiring patents and soaring development costs are propeling drug makers into one another's arms. Merck's roughly $41 billion cash-and-stock deal to acquire Schering-Plough Corp. (SGP) continued a consolidation race that began this year with Pfizer Inc.'s (PFE) planned acquisition of Wyeth (WYE). Earlier Tuesday, Schering-Plough reported first-quarter net income more than doubled, topping expectations, amid prior-year acquisition charges.

The Merck-Schering-Plough deal would bring together two companies which already have a relationship through their cholesterol-drug venture. That effort has been under pressure for a year following an early 2008 study that raised questions about the safety and effectiveness of the drugs Vytorin and Zetia. The venture's sales fell 23% in the first quarter.

Merck's net income dropped to $1.43 billion, or 67 cents a share, from $3.31 billion, or $1.52 a share, a year earlier. Excluding items including the gains and charges, earnings fell to 74 cents from 89 cents.

Sales fell 7.5% to $5.39 billion, with the stronger dollar contributing 3 percentage points of the decline.

Analysts polled by Thomson Reuters were expecting earnings, excluding items, of 77 cents a share on revenue of $5.77 billion.

Gross margin fell to 75.2% from 78.7%, amid restructuring costs and a drop in volume.

Sales of Merck's hit cervical-cancer vaccine, Gardasil, fell 33%. Merck has said it sees flat Gardasil sales in 2009.

Asthma and allergy drug Singulair recorded a 4% sales decline. U.S. sales have been hurt by an over-the-counter version of rival drug Zyrtec by Johnson & Johnson (JNJ) as well as by concerns about a Food and Drug Administration alert of a possible association between Singulair and suicide.

-By Mike Barris, Dow Jones Newswires; 201-938-5658; mike.barris@dowjones.com