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Aug. 24, 2009 -- ''Lethal levels" of the anesthetic propofol (Diprivan) killed Michael Jackson, according to news reports, which cited information from a search warrant affidavit unsealed in Houston.
The court documents said the Los Angeles County Coroner's Office reached that conclusion after an autopsy of the pop star, who died June 25.
But an anesthesiology expert cast doubt on that conclusion, saying that the doses mentioned in news reports are "inconsistent with a lethal level of propofol'' and that a drug cocktail likely killed the star.
According to the Los Angeles Times, Jackson's personal doctor, Conrad Murray, MD, told detectives at the Los Angeles Police Department that he had been treating Jackson for insomnia for about six weeks.
The Los Angeles Times said Murray had given Jackson 50-milligram doses of propofol in the past and had lowered them to 25 milligrams to wean him off the powerful anesthetic, which is used to sedate patients during surgery. Murray said when he lowered the propofol dose he also mixed in two other sedatives, lorazepam (Ativan) and midazolam (Versed).
But 50 milligrams of propofol for a person with Jackson's slender frame is typically far from lethal, says Hector Vila Jr., MD, a Tampa, Fla., anesthesiologist and chairman of the Ambulatory Surgery Committee for the American Society of Anesthesiologists.
Vila tells WebMD, ''Based on FDA-approved prescribing information, sedation would be initiated with about 27 milligrams in a patient Michael Jackson's size."
But "the doses that Dr. Murray describes as having administered to Michael Jackson would not normally be considered adequate to result in a 'lethal' blood level of propofol," he says.
A drug cocktail likely killed the star, he suspects, after taking into consideration the other drugs allegedly given Jackson during his final days. "If mixed with other medications, even a small amount of propofol as described by Dr. Murray could result in respiratory arrest," Vila says.
Ativan and Versed are benzodiazepines, like Valium, which produce a calming effect. Versed is very short-acting and is often used, for instance, during a colonoscopy.
''When you start mixing propofol with other medications, that is when the wheels start coming off and the safety profile of this medication becomes lessened," says John Dombrowski, MD, a Washington, D.C., anesthesiologist and member of the board of directors of the American Society of Anesthesiologists.
Both Ativan and Versed are respiratory depressants, he says. ''You put them on top of propofol, and you're dead.''
One piece of critical information is missing, Dombrowski tells WebMD: the rate of administration. "How fast was the 25 or 50 milligrams being administered?" he asks. "Over an hour? 15 minutes? One minute?"
The Los Angeles County Coroner's Office responded to a request for information with an email, stating, "We have no comment on the story that is circulating."