WASHINGTON — House Democrats are questioning whether Merck and Schering-Plough made up information about a meeting of medical experts to discuss Vytorin, after lawmakers began investigating a failed study of the drug.

Democratic leaders of the House Energy and Commerce Committee sent a letter to the companies yesterday asking why minutes from a November meeting about the blockbuster cholesterol drug were created after the fact, in December. The five-member panel of medical advisers was told that no minutes would be taken or transcript of the meeting made, the lawmakers note.

Committee chairman John Dingell and Subcommittee for Oversight chairman Bart Stupak are investigating how Merck and Schering-Plough handled data comparing Merck's Zocor against their new drug Vytorin.

A study was completed in 2006 and showed that Vytorin was no better at limiting plaque buildup in neck arteries than Zocor. But the companies didn't release those results until January, after Congress began investigating the delayed study.

E-mails released yesterday show James Stein, a University of Wisconsin professor, objecting to Merck's recollection of the Nov. 16 meeting.

"I still have a hard time calling this document 'minutes,' " wrote Stein, in an e-mail to Merck executives. "They at best are an incomplete summary of what transpired at the meeting."

Stein takes issue with Merck's statement that panelists unanimously recommended changing a key goal of the Vytorin study.

"This really overstates our recommendation," Stein wrote. "It was the decision of the company to change the endpoint."

Stein concludes his Jan. 3 e-mail by telling Merck he will not approve its version of the meeting.