GlaxoSmithKline P.L.C. for years ignored evidence that its antidepressant Paxil may have caused birth defects, a lawyer told a Philadelphia jury yesterday on behalf of a woman who says that taking the drug during her pregnancy caused her 3-year-old son's heart problems.

London-based Glaxo, which employs several thousand in the Philadelphia region, also told its scientists to avoid disclosing possible risks associated with the drug's use by pregnant women, said the lawyer, Sean Tracey.

Tracey represents Bensalem resident Michelle David, a former cheerleader for the Philadelphia 76ers, who is making the claim for her son, Lyam Kilker. The boy appeared briefly in the courtroom yesterday.

GlaxoSmithKline's lawyer Chilton Varner said there is no evidence that Paxil caused Lyams's heart problems.

The case is being heard by Judge Stephen Levin in Common Pleas Court.

Tracey said that in early tests, rats administered the drug were more likely to have pups that didn't survive past four days.

In the late 1980s, an internal Glaxo scientist warned that "there remains the possibility" that Paxil could cause birth defects at higher doses," according to one document Tracey displayed. Tracey said Glaxo had avoided for 20 years finding out why the rats died.

The trial is the first of more than 600 cases alleging that Glaxo knew Paxil caused birth defects and hid those risks to pump up profits. Approved for U.S. use in 1992, the drug generated $942 million in sales last year, 2.1 percent of Glaxo's total sales.

Glaxo lawyer Varner said the company reported any sign of problems to federal authorities. She accused Tracey of cherry-picking sentences from documents. When jurors see all the evidence, she said, they will realize "Paxil has been tested in trials as much as any drug ever."

Varner also said that even though Lyam was hospitalized for five months after his birth and underwent surgeries to repair his heart, the boy today "has no cardiac symptoms . . . is at preschool and runs and walks like a 4-year-old should."

Tracey said Lyam eventually will need another surgery. He also painted Glaxo as consistently denying problems with one of its best-selling drugs.

By 1997, the company received reports of 50 miscarriages or intrauterine deaths. When Glaxo studied whether there was a connection between Paxil and birth defects, its scientists called the number of cases an "alarming finding." But they did not include those words in the final version of the report or give the report to the U.S. Food and Drug Administration, even though it was required to do so, Tracey said.

Also in 1997, GSK executive Bonnie Rossello wrote a memo saying that if the company had to conduct animal studies it could "bury" negative results, Tracey said.

Tracey said that in 2001, after a woman reported to Glaxo that she had been taking Paxil and had terminated her pregnancy because of birth defects, company scientists said they were "almost certain" that Paxil had caused the birth defects. But GSK did not tell the woman or the FDA that, Tracey told the courtroom.

"What they did next was nothing," he said.

The FDA initially classified Paxil as a drug with no known connections to birth defects. In 2005, the agency reclassified it as a drug with some evidence of human fetal risk but allowed doctors to continue prescribing the drug to women of childbearing age if the benefits outweigh the risks.