In paragraph 8, corrects to say $60 million against Mead Johnson and $495 million against Abbott, not $60 million against Abbott and $495 million against Mead Johnson; in paragraph 9 corrects date of defense verdict to October, not November; in paragraph 11 corrects that AAP filed brief supporting Mead Johnson, not Abbott.

By Diana Novak Jones and Brendan Pierson

May 2 (Reuters) - A federal judge on Friday said she will allow expert testimony that formula made by Abbott Laboratories ABT.N and Reckitt Benckiser RKT.L subsidiary Mead Johnson for premature babies can cause a fatal intestinal illness, as the companies face hundreds of lawsuits over the claims.

U.S. District Judge Rebecca Pallmeyer in Chicago said she will allow the experts to testify in future trials over claims that cow’s milk-based formulas made by Abbott and Mead Johnson cause the illness in some premature babies.

But in a separate order issued on Friday, Pallmeyer sided with Abbott in a lawsuit that was the first one slated to go to trial next week in federal court out of more than 700 similar cases that have been centralized in her court.

The judge said the family of RaiLee Mar, an infant who was born prematurely and died of necrotizing enterocolitis after receiving some of Abbott’s formula, had failed to show that the company's alleged failure to warn doctors and Mar’s family about the risks of the disease was the cause of Mar’s illness or that there was a reasonable alternative way the formula could have been made.

Representatives for Abbott and Mead Johnson did not immediately respond to requests for comment.

All of the lawsuits allege that the companies failed to warn that their specialized formulas used by newborn intensive care units in hospitals could cause necrotizing enterocolitis, a disease that almost exclusively affects premature infants and has an estimated mortality rate of more than 20%.

The companies have denied the claims, saying that while breast milk protects against NEC, formula does not cause it, and that the benefits of breast milk have long been known to clinicians.

In addition to the federal cases, both companies face hundreds of state court cases around the country, which have already resulted in verdicts of $60 million against Mead Johnson and $495 million against Abbott.

Both companies prevailed in the most recent trial, in October. However, the judge in that case in March ordered a new trial, finding that lawyers for the defendants had acted improperly.

The litigation has raised alarm from many doctors who say it could threaten the formulas' availability or affect medical decisions.

The American Academy of Pediatrics recently filed a brief supporting Mead Johnson in its appeal of the verdict against it last year, saying that formula is part of the standard of care for premature babies.

U.S. regulatory agencies and a working group of scientists convened by the National Institutes of Health said in a joint report last year that current evidence does not support the hypothesis that formula causes necrotizing enterocolitis.

(Reporting by Brendan Pierson in New York and Diana Novak Jones in Chicago, Editing by Alexia Garamfalvi and Matthew Lewis)

((Brendan.Pierson@thomsonreuters.com; 332-219-1345 (desk); 646-306-0235 (cell);))