According to a doctor, Springfield murder defendant Elizabeth McKeown ran over and killed a woman after losing contact with reality due to a toxic level of a cough syrup ingredient in her system.

Barbara Foster was killed November 2018, and McKeown’s murder trial began this week.

“I do believe it contributed to her erratic behavior,” said Dr. Leigh Anne Nelson, a forensics psychiatric pharmacist and an associate professor at the University of Missouri at Kansas City.

Emily Shook, first assistant prosecuting attorney in Greene County, asked Nelson to elaborate by explaining what else might have “contributed” to the erratic behavior that led to McKeown, 49, killing Foster, who was 57.

In response, Nelson made her conclusion more certain and direct.

Dr. Leigh Anne Nelson (Photo: UMKC)

“I consider the ’cause of her behavior’ and ‘contributed to her behavior’ as being one and the same,” Nelson said.

This case is one of the few in the United States in which a murder defendant has mounted a defense based on an alleged psychosis caused by over-the-counter cough syrup. It is not known if such a defense has ever been successful in a murder case.

Nelson provided testimony in a video that was recorded earlier. It was shown to jurors Wednesday.

Police immediately suspected McKeown was under the influence of something.

Her responses to questions and her behavior seemed confused and erratic.

But alcohol and drug testing showed there was no alcohol in her system and the only drugs found were from her medications for depression and diabetes — and for the drug dextromethorphan, a key ingredient in almost all cough syrups.

Police have known since the day of the death that cough syrup might be an issue. A detective went to McKeown’s home that night and retrieved an empty bottle of cough syrup from the trash at the curb.

Nelson was hired by McKeown’s lawyer to review lab results, police reports and to testify.

How can cough syrup cause confusion?

Elizabeth McKeown (Greene County Jail)

She testified that McKeown had bought over-the-counter Delsym 12-hour, extended-release cough syrup.

Most who take the cough syrup should have a residual of 5 nanograms of dextromethorpan or less per milliliter in their system.

McKeown had a level of 350. Nelson testified that toxicity sets in at about a level of 200.

When Nelson saw the 350 figure, she testified, she suspected McKeown might be among the 6 percent of white Americans who have livers that cannot metabolize the drug.

So McKeown’s liver was tested and, Nelson said, the results showed her liver does not metabolize dextromethorphan.

Nelson explained it this way: 75 percent of all drugs are broken down by one particular “pathway” of enzymes that are in the liver. In McKeown, she said, this pathway does not work when it comes to dextromethorphan.

For most people, she testified, the drug is out of the body in six to 10 hours.

For people like McKeown, she testified, it is out of the body in 30 to 65 hours.

(According to previous testimony, McKeown was sick and coughing and took cough syrup earlier in the day. Foster was run over at about 5:15 p.m.)

Shook asked Nelson if she was aware of any homicide being linked to dextromethorphan.

Nelson said she was not, but had not been asked to research that topic.

“Obviously, it is not going to be a common occurrence or the product would not be available over-the-counter for the public to buy,” Nelson said.

Shook asked Nelson if there were people who deliberately misuse cough syrup.

Nelson said, yes, “mostly teenagers.”

She added that it seemed unlikely McKeown would have bought the extended-release cough syrup if her intent was to try to get the feeling of euphoria some get with abuse of cough syrup.

(Other side effects are less desirable, such as lack of mental clarity, memory loss and lack of physical coordination.)

Shook asked if it were possible that McKeown might have drunk the whole bottle at one time.

No, Nelson said. If McKeown had done that the level would have been well beyond the reading of 350.

Toxicity mimics effects of intoxication

Nelson testified that when people overdose on dextromethorphan — and sometimes die — it is at levels of 3,300 and above.

Nelson testified that it was her conclusion that McKeown took the recommended dose as suggested on the bottle and that the drug was in toxic levels in her body because her liver could not break it down.

According to Nelson, when people have dextromethorphan toxicity they appear as if they are drunk.

After the death, police gave McKeown various tests, including field sobriety tests. She failed most of the field sobriety tests, including the horizontal gaze nystagmus test.

This is the test where an officer asks you to follow a finger moving horizontally across your field of vision without moving your head.

Nelson testified that someone suffering from dextromethorphan toxicity would fail that test. McKeown did fail it.

Someone with dextromethorphan toxicity, she testified, “could be a danger to themselves or to someone else.”

The prosecution rested its case Wednesday morning.

McKeown’s daughter then testified on behalf of her mother.

She said the one odd thing she noticed about her mother on the day of the death was that her mother used the phrase “red tomato” and laughed whenever she said it.

She did not know why her mother was saying it.

Police officer Justin Lloyd, who testified Tuesday, was the first officer to talk to McKeown after the incident. McKeown was still in her car and Lloyd approached with his gun drawn.

He said he asked McKeown her name and she said, “red tomato.”

When he asked her where she lived, she responded, “Up your butt and around the corner, officer.”

The trial continues June 9. It is expected to be in the hands of the jury by the end of the day.

Steve Pokin

Steve Pokin writes the Pokin Around and The Answer Man columns for the Springfield Daily Citizen. He also writes about criminal justice issues. He can be reached at spokin@sgfcitizen.org. His office line is 417-837-3661. More by Steve Pokin