A U.S. judge refused to issue a temporary restraining order blocking the approval of new generic versions of AstraZeneca's blockbuster cholesterol drug Crestor in the United States.

U.S. District Judge Randolph Moss in Washington, D.C. ruled that AstraZeneca was not likely to win a lawsuit claiming it should get seven more years of exclusive rights to the drug thanks to its recent approval to treat a rare pediatric illness.

Generic drugmakers including Novartis AG unit Sandoz, Apotex and Mylan have said in court filings that they are prepared to launch generic versions of Crestor, which lost patent protection earlier this month.

AstraZeneca spokeswoman Michele Meixell said in an emailed statement the company was "disappointed" with the decision.

AstraZeneca's bid to extend its exclusivity had drawn sharp criticism from former presidential candidate and Senator Bernie Sanders, a Democrat from Vermont, who along with seven Democratic U.S. Representatives had urged the U.S. Food and Drug Administration in a July 7 letter not to let the company exploit a "loophole."

Allergan plc has already been selling generic Crestor in the U.S. since May under a licensing agreement with AstraZeneca, and is not affected by order.

Crestor, which accounted for more than 20 percent of AstraZeneca's $23.6 billion in sales last year, was approved by the FDA for the treatment of high cholesterol in 2003.

In May, the FDA approved the addition of a new indication for use to the drug's label for the treatment of homozygous familial hypercholesterolemia in patients 7 to 17 years old. The rare genetic disease, which causes high cholesterol and sometimes heart disease, affects about one in a million people.

In June, AstraZeneca won seven years of exclusive marketing rights for the new indication under the federal "orphan drug" program. Orphan drug exclusivity is granted to new drugs or new indications of existing drugs for rare diseases, to encourage research that might otherwise not be profitable.

AstraZeneca then sued the FDA seeking to block final approval of any new generic Crestor. The company claimed that federal law required drugs to include all pediatric indications on their labels.

Moss's decision is in line with a ruling last year by another judge in the same court, who allowed generic versions of Otsuka's antipsychotic drug Abilify to go on the market even though the drug had recently been approved for a rare disease.