Food and Drug Administration (FDA) has delayed the approval of Brilinta, a drug for blood flow produced by AstraZeneca, which will be a major competitor of Plavix, made by Sanofi-Aventis and Bristol-Myers Squibb, the closest second in the world based on sales.
AstraZeneca said it had received a letter from the authority, which requires further analysis of clinical test data, but no additional studies.
Most analysts anticipate that FDA will approve Brilinta until December 20, especially because the deadline has been postponed on 16 September.
Shares of the British group, AstraZeneca, which reached the last meeting the highest level since late October, fell 5.5% to £2.98 per unit.
The company relies heavily on revenue that will be brought Brilinta, already approved in Europe to offset the expiration of patents for some of the best selling drugs, and NEXIUM (for heart disease) and Seroquel (for schizophrenia).
Delaying approval in the U.S. will reduce confidence in the potential drug in the U.S., where it is anticipated that sales will contribute about 10% to group results by 2015.
Analysts have forecast that annual sales could reach into the future Brilinta 2.7 billion dollars.