A forensic toxicologist at the laboratory that tested George Floyd’s blood said it was common for intoxicated driving suspects who used fentanyl to have higher levels of the drug in their systems than Mr. Floyd did when he died. Prosecutors hoped his testimony would strike a blow to the argument by Derek Chauvin’s lawyer that Mr. Floyd’s death may have been an overdose.
The toxicologist, Dr. Daniel Isenschmid, works at N.M.S. Labs in Pennsylvania and testified on the ninth day of the trial against Mr. Chauvin, who has been charged with murder in Mr. Floyd’s death. Of more than 2,300 blood samples from intoxicated drivers that N.M.S. Labs tested last year — all of which were in cases where the driver survived and tested positive for fentanyl — about a quarter of the people had fentanyl levels that were the same or higher than Mr. Floyd’s, Dr. Isenschmid said.
Prosecutors had called him to the stand to rebut the argument from Mr. Chauvin’s lawyer that fentanyl, a powerful opioid, had caused Mr. Floyd’s overdose. Prosecutors say Mr. Chauvin is responsible for Mr. Floyd’s death, and earlier on Thursday, a lung doctor testified that Mr. Chauvin’s knees on Mr. Floyd’s neck and back were significant factors in his death.
Dr. Isenschmid said that last year, in cases where N.M.S. Labs tested blood from a person who died and who had taken fentanyl, the average amount that scientists found was 16.8 nanograms per milliliter, about 50 percent higher than the amount found in Mr. Floyd’s blood. But Mr. Chauvin’s lawyer, Eric J. Nelson, noted that average was among people who died of any cause and had fentanyl in their system, not just overdoses. And, he pointed out, the median level of fentanyl among that group was slightly below Mr. Floyd’s.
The testimony from Dr. Isenschmid, who previously worked as the chief toxicologist at the Wayne County medical examiner’s office in Detroit, was some of the most technical yet, but jurors appeared attentive, according to a reporter in the courtroom.
He said that as a person’s body processes fentanyl, it is turned into norfentanyl, and that Mr. Floyd had a relatively high proportion of norfentanyl, indicating that his body had already processed a substantial portion of fentanyl. That bolstered prosecutors’ argument that Mr. Floyd had not overdosed; fentanyl overdoses often occur shortly after the drugs are taken, before a person’s body can break down much of the drug.
But Dr. Isenschmid conceded, in response to Mr. Nelson, that it was also possible that Mr. Floyd had taken and processed fentanyl earlier in the day and then taken more in the moments before or during the arrest. The toxicology results, Dr. Isenschmid said, do not indicate when a specific amount of fentanyl was taken.
Mr. Nelson has pointed out that pills that had Mr. Floyd’s D.N.A. on them and may have been partially ingested were found in the back of the police car in which Mr. Floyd was briefly placed.
Still, Dr. Isenschmid said the same amount of fentanyl can have very different effects in a new user as opposed to someone who is addicted to the drug. Mr. Floyd’s girlfriend has said she and Mr. Floyd both struggled to stop using opioids.
“If a person becomes tolerant to a drug, they require more and more to get the desired effect,” Dr. Isenschmid said.
Methamphetamine was also found in Mr. Floyd’s system, though Dr. Isenschmid said the levels were so low that it likely had no intoxicating effect.