Pharmaceuticals giant AstraZeneca said profits fell by more than a third in the first quarter after a number of patents ran out and it was hit by tough market conditions.
This led it to downgrade its full year earnings prospects.
The company also announced that Chief Executive David Brennan would retire in June.
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Revenues came in well below market expectations, falling 11% to $7.349bn, short of consensus forecasts of $7,874m.
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Loss of exclusivity on several key brands accounted for eight percentage points of the revenue decline, the firm said.
The company reported profit before tax fell 38% to $2.053bn with earnings per share (EPS) also down 38% to $1.28.
Brennan said the anticipated impact from the loss of exclusivity on several brands, together with challenging market conditions, had made for a difficult start to the year.
"Delivery on our restructuring plans and continued discipline on operating costs, together with the benefits from a lower tax rate, will only partially mitigate the revenue pressures," he said.
"As a result we have lowered our Core EPS target for the full year to the range of $5.85 to $6.15."
Following the results the firm also released a statement detailing Brennan's departure after six years in the job.
Chief Financial Officer Simon Lowth is to act as interim Chief Executive Officer from the start of June until a permanent successor is in place.
Julie Brown, Vice President Group Finance, will become interim Chief Financial Officer at the same time.
"David has led AstraZeneca's business with skill, integrity and courage during a period of enormous change for the pharmaceutical industry and for the company," said Chairman Louis Schweitzer.
"We fully understand and respect David's decision to retire and thank him for his selfless leadership of the company."
