The U.S. Supreme Court on Wednesday rejected a request by
to block other companies from selling cheap copies of Norvasc, which produced sales of $4.9 billion last year.
Justice John Paul Stevens' decision to turn down Pfizer's emergency appeal means
can keep selling generic versions of the blood-pressure drug that is Pfizer's second-biggest product.
Pfizer can ask another justice to halt the sales.
Mylan began selling its drug on March 23, and Apotex entered the market on May 24. Pfizer is selling a low-price version, too, as well as brand-name Norvasc.
Pfizer had been counting on Norvasc remaining free from generic competition in the U.S. until September, but several
legal defeats invalidated Pfizer's patent and prompted the generic-drug makers to launch their versions.
The generics' impact on Norvasc
has been dramatic. By May 25, Mylan's generic accounted for about 58% of total prescriptions, Pfizer's generic had 30%, and brand-name Norvasc had the rest, according to research by A.G. Edwards and IMS Health.