A man walks past Pfizer's world headquarters in New York April 28, 2014. Reuters/Andrew Kelly

(Reuters) - Pfizer Inc (PFE.N), the biggest U.S. drugmaker, on Monday reported revenues well below Wall Street expectations, hurt by falling sales of generic medicines it calls established pharmaceuticals.

Pfizer, which is trying to take over Britain's AstraZeneca PLC (AZN.L), earned $2.33 billion, or 36 cents per share, in the first quarter ended March 31. That compared with $2.75 billion, or 38 cents, in the year-earlier period, when the company reported gains from the transfer of product rights.

Excluding special items, Pfizer earned 57 cents per share. Analysts, on average, expected 55 cents per share, according to Thomson Reuters I/B/E/S. Total revenues fell 9 percent to $11.35 billion, which was $730 million below Wall Street expectations.

Pfizer pulled its prior 2014 forecast, saying it will update its outlook its outlook "as soon as practicable."