Shares of U.K. drugmaker AstraZeneca PLC (NYSE: AZN) are plunging after the U.S. Food and Drug Administration requested further analysis of existing studies of the company’s heart drug, Brilinta, thereby further delaying its potential approval.

Analysts now estimate final approval of the drug may take another six to twelve months.
As of 12 pm (EST), AstraZeneca shares were down 7.15 percent on the New York Stock Exchange – the stock had also fallen about 6.7 percent on the London bourse.

Jefferies International indicated that AstraZeneca is facing patent expiry of a number of its drug products in the coming year, including schizophrenia drug Seroquel and heartburn relief Nexium. Brilinta is one of the few promising new drugs, sales of which the company hoped would be able replace lost revenue.

“This delay will come as a disappointment to many and may also start to raise uncertainties about the potential scale of the product’s likely commercial success,” the broker said in a note.

Brilinta has already endured lengthy delays in the U.S. after a September trial in North American failed to produce any significant benefits for patients. Brilinta has already received regulatory approval in Europe and is expected to generate $2-billion in sales upon approval, making it a legitimate ‘blockbuster’ drug.