The disappointing news added urgency to the New York company's efforts to acquire rival
For the three months ended March 30, Pfizer said its profit was $2.33 billion, or 36 cents a share. That is down from $2.75 billion, or 38 cents a share, in the same period a year ago. Revenue fell 8.5% to $11.35 billion.
Frank D'Amelio, Pfizer's chief financial officer, said the first-quarter performance was in line with the company's expectations.
It "reflected the continuing impact of product losses of exclusivity, the expiration and near-term termination of certain collaborations and an operating environment that remains challenging," he said in a Monday statement.
Drugs that face generic rivals include cholesterol medication Lipitor and bladder drug Detrol LA.
Pfizer, which first approached the British company AstraZeneca in January with an offer, said last week that it has increased its takeover bid to more than $106 billion, or about $84.47 a share. AstraZeneca dismissed the deal as "substantially" undervaluing its worth.
Still, the company on Monday said it hopes its sweetened bid will entice AstraZeneca to "engage with Pfizer and enter into discussions" regarding a possible merger of the two drug makers.