June 20 (Reuters) - A bid by GSK and other

drugmakers to stop more than 70,000 lawsuits in Delaware over

discontinued heartburn drug Zantac has received the backing of

leading U.S. industry groups, including the United States

Chamber of Commerce and Pharmaceutical Research and

Manufacturers of America.

In a friend-of-the-court brief posted to the Delaware

Superior Court's docket on Thursday, the groups said that a

Delaware judge's recent ruling allowing the lawsuits to proceed

jeopardized the state's business-friendly reputation and

threatened to turn it into "a hotbed of products-liability and

mass-tort litigation."

GSK, Pfizer ( PFE ), Sanofi and Boehringer

Ingelheim, which all sold Zantac at times, had asked Judge

Vivian Medinilla to bar plaintiffs from offering expert

testimony linking Zantac to cancer, arguing that it was not

based on sound scientific methods. The plaintiffs' cases depend

on that testimony, and cannot go to trial without it.

After the judge refused, the companies petitioned her for

leave to appeal directly to the Delaware Supreme Court. The

industry groups in Thursday's filing are asking the judge to

grant that petition.

The groups, which also include the National Association of

Manufacturers and the Biotechnology Innovation Organization,

said Medinilla's ruling was at odds with a Florida federal court

that in 2022 tossed about 50,000 Zantac claims after rejecting

similar evidence as unreliable. Some plaintiffs are appealing

that ruling.

If Delaware courts adopted a more relaxed evidence standard

for mass tort cases, they said, the state would quickly become a

venue of choice for plaintiffs since many U.S. companies are

incorporated there.

The groups urged Medinilla to "consider the importance to

the business community of clarity, consistency and

predictability in Delaware jurisprudence on expert testimony."

A lawyer for the plaintiffs did not immediately respond to a

request for comment.

First approved in 1983, Zantac became the world's

best-selling medicine in 1988 and one of the first to top $1

billion in annual sales. It was originally marketed by a

forerunner of GSK and later sold successively to other

companies.

Lawsuits began piling up after the U.S. Food and Drug

Administration in 2020 asked manufacturers to pull the drug off

the market over concerns that its active ingredient, ranitidine,

could degrade into a cancer-causing chemical called NDMA over

time or when exposed to heat.

The drugmakers have maintained there is no evidence Zantac

exposes users to harmful NDMA levels or causes cancer.

The vast majority of pending cases are in Delaware. Only one

case, against GSK and Boehringer Ingelheim in Illinois, has gone

to trial, ending in a victory for the companies last month.