May 20 (Reuters) - GSK has been sued by an

independent Connecticut laboratory that accused the drugmaker of

defrauding the U.S. government and taxpayers by concealing

cancer risks in Zantac, once a blockbuster heartburn drug.

In a whistleblower complaint filed on Monday, Valisure said

GSK violated the federal False Claims Act by hiding the risks

for nearly four decades while Medicare, Medicaid and other

health programs covered billions of dollars of prescriptions.

The New Haven-based lab said its testing in 2019 revealed

that Zantac, also known as ranitidine, could form a

cancer-causing carcinogen known as NMDA and was therefore "unfit

for human consumption."

It said GSK concealed the same result from the U.S. Food and

Drug Administration, which approved Zantac in 1983.

Valisure is seeking billions of dollars in damages from GSK,

including civil fines of up to $11,000 per violation, in a

complaint filed in Philadelphia, where some of the British

drugmaker's operations are based.

Its lawyers also represent thousands of plaintiffs in

personal injury lawsuits against GSK and other companies that

have sold ranitidine.

In a statement, GSK said it will defend against Valisure's

meritless lawsuit, and that the FDA has found the lab's tests

"scientifically flawed and unreliable."

GSK also said there remains no consistent or reliable

evidence that ranitidine increases cancer risks.

The False Claims Act lets whistleblowers sue on behalf

of the federal government, and share in recoveries.

Valisure first sued GSK on behalf of the United States and

more than two dozen states in 2019, in a case filed under seal.

The federal government declined to join the lawsuit in

March, leaving Valisure to sue on its own.

Zantac became the world's best selling medicine in 1988, and

was one of the first drugs to top $1 billion in annual sales.

The FDA asked drugmakers in April 2020 to pull Zantac and

generic equivalents off store shelves after finding NDMA in

samples, citing what Valisure said was its testing.

Two years later, a federal judge dismissed about 50,000

Zantac claims after rejecting the plaintiffs' scientific

experts. Some of those cases are being appealed.

More than 70,000 private lawsuits over Zantac remained

pending this month in U.S. courts. Most are in a Delaware state

court, where a judge is weighing whether the cases can proceed.

The first trial over Zantac's link to cancer began this

month in Chicago, and may end this week.

The case is U.S. ex rel Valisure LLC v GlaxoSmithKline Plc

et al, U.S. District Court, Eastern District of Pennsylvania,

No. 19-04239.