Dr. Douglas Carlson, an emergency room pediatrician at St. Louis Children's Hospital and Washington University School of Medicine, said the coroner's report makes sense.
"While death is an unusual side effect of dextromethorphan, it is known to occur," said Carlson, who did not treat Kimber. "The efficacy of over-the-counter cough medications is minimal in children, so we recommend not using them in less than 2 years and be careful with those under age 6."
According to the coroner's report, Kimber complained of leg pain, cramps and muscle spasms hours before her death. Huser said that was consistent with drug toxicity as her body began to shut down.
Carlson said those symptoms were inconsistent with dextromethorphan, which causes "drowsiness and fatigue."
An overdose of dextromethorphan usually triggers changes in the child's mental status leading to "irritability and confusion," according to Carlson. "That's why teens use it to get high -- for the sensory perceptions."
The drug in higher doses can cause cardiac abnormalities and arrhythmias that can cause the heart to stop functioning, he said.
"Dextromethorphan is the most common ingredient in the country," said Carlson. "When you use it with small children, make sure to follow the label directions and measuring device with the bottle."
"I am not aware of fatal reactions when used alone," he said.
As cetirizine, found in the allergy medicine Zyrtec, Carlson said the package warns that when used with dextromethorphan, the combination can depress the central nervous system or lead to psychomotor impairment.
That drug could have explained the cramping and twitching, according to Dr. John Spangler, an associate professor of family and community medicine at Wake Forest University School of Medicine.
"Instead of sedation, which can occur with antihistamines, some children have a paradoxical reaction," he said.
But, warned Dr. Donna Seger, medical director of the Middle Tennessee Poison Center, there could have been other issues at play, such as a viral or other infection.
"Had she seen a physician?" she asked.
"We shouldn't cause a scare about these drugs unless we have evidence that they caused a problem," said Seger. "A lot of children take these drugs."
ABC's Dr. Christopher A. Tokin contributed to this story.