(Nam Y. Huh/AP file)

The girl's parents were both smokers. Both of them had been vaping as well.

Her mother had purchased highly concentrated liquid nicotine for the e-cigarettes, diluted it with vegetable glycerin and put it in an empty children's ibuprofen bottle. In faint, handwritten letters, it was labeled “NIC.”

But when the 6-year-old girl's father went looking for the children's pain reliever one day in the summer of 2015, he grabbed the concoction from the refrigerator by mistake — and gave his daughter a dangerous dose, according to data from a case report published this month in the Annals of Emergency Medicine.

The girl, who had been taking pain reliever for a sprained ankle, immediately felt a burning sensation in her mouth and throat, according to the case report.

Her father tasted the substance and realized his mistake.

Her mother tried to force the child to vomit, but she lost consciousness and had a seizure.

When paramedics arrived at the Oregon home, the girl was awake but not responding to their questions, and she was rushed to a nearby hospital, according to the report.

Medical experts warn that incidents like these illustrate the deadly dangers children face as e-cigarettes — and liquid nicotine — become increasingly popular.

“Generally, it has become more common, and our concern is that it will continue to do so because there is a greater availability of more highly concentrated nicotine products,” Matt Noble, a medical toxicology fellow with the Oregon Poison Center and instructor at the Department of Emergency Medicine at Oregon Health and Science University, said in an interview.

Noble, who co-authored the case report, said that although children in the past may have chewed on cigarettes or gotten into their parents' nicotine patches, the amount of nicotine in those products was “relatively low.”

With liquid nicotine, however, “the potential for toxicity is relatively unprecedented,” he said, noting that it not only comes in high volumes but also is highly concentrated.

The federal government is attempting to regulate the e-cigarette industry, and although experts agree that these efforts may be beginning to pay off, they say there is still a long way to go.

The U.S. surgeon general has called the rising use of e-cigarettes among children and young adults a “major public health concern.” As The Post's Brady Dennis reported, the number of middle-school and high school students who report having used them has tripled over the past five years, and the number of young adults (ages 18 to 24) has doubled.

“We know enough right now to say that youth and young adults should not be using e-cigarettes or any other tobacco product, for that matter,” Surgeon General Vivek H. Murthy said in an interview last month. “The key bottom line here is that the science tells us the use of nicotine-containing products by youth, including e-cigarettes, is unsafe.”

But experts say e-cigarettes products, namely liquid nicotine, pose a problem even for children who don't smoke — because of how they're marketed and sold to consumers.

Kyran Quinlan, head of the American Academy of Pediatrics Council on Injury Violence and Poison Prevention, said the case study out of Oregon is unusual. More often, Quinlan said, accidental ingestions happen when children find the liquid nicotine, which comes in candy-like flavors and is packaged in bright colors, and drink it of their own accord.

“From all the toxicologic science known, small sips of around a teaspoonful of concentrated nicotine from one of these containers could be enough to kill a toddler,” he said.

“Nicotine is a neurotoxin and can have severe effects on young children including loss of consciousness, alteration of breathing, and changes in heart rate and blood pressure,” he added. “The child who is described in the case report likely survived because of the quick response on the part of the parents to seek care and the excellent care provided in the emergency room and intensive care unit.

“The amount this child ingested is above the range of a lethal dose.”

The girl survived and was eventually released from the hospital. But in 2014, a 1-year-old boy in Upstate New York died after accidentally ingesting liquid nicotine, authorities said at the time.

The Oregon case also revealed another danger of liquid nicotine.

The case study explained that the girl's mother had bought a liter of concentrated unflavored liquid nicotine online and diluted it according to the instructions. Noble, the report's co-author, said the manufacturer's label stated that the bottle contained a nicotine concentration of 60 mg/mL when, in reality, testing suggested it contained a concentration of 140 mg/mL.

Even after the mother diluted it, the product was much stronger than she ever would have known.

“I think it highlights what might be a more common problem than we realize,” Noble said.

The girl, who was not named in the report, was rushed to an emergency room with a decreased heart rate and an inability to properly breathe; doctors had to intubate her. She was vomiting, sweating, drooling and shaking. “Her mental status fluctuated between agitation and unresponsiveness,” the researchers wrote in the report.

The girl had ingested about 703 mg of liquid nicotine; a traditional cigarette delivers between 0.2 and 2.4 mg of nicotine.

A lethal dose of nicotine for adults has been estimated to be about 50 to 60 mg, according to data released by the Centers for Disease Control and Prevention.

In 2016, there were 1,492 instances of exposure to e-cigarettes and liquid nicotine reported to poison control centers across the country, according to preliminary data from the American Association of Poison Control Centers. In 2014 and 2015, there were more than 3,000 incidents each year, though, the agency explained, not all of the exposures were poisonings or overdoses.

Although the exact cause of the drop in exposures is unclear, those who study the industry believe it's a combination of education, awareness and possibly government regulation, which is slowly catching up.

But Elizabeth Scharman, director of the West Virginia Poison Center, said most of the regulations were not implemented until later in 2016, which would not explain the decline during the first part of the year.

The federal government began regulating the e-cigarette industry for the first time last year.

The U.S. Food and Drug Administration restricted the sale of e-cigarettes to minors younger than 18 and required manufacturers to disclose their ingredients and send their products to the FDA for approval.

At the same time, the Consumer Product Safety Commission began imposing certain standards, such as the child-resistant packaging for liquid nicotine.

Still, Quinlan, with the American Academy of Pediatrics, said things have been slow to change. He said he has seen vape shops continue to sell products in non-child-resistant bottles and noted that once the bottles have been opened, children can easily access the potent contents.

“We remain deeply concerned about the risks of unintentional ingestion of liquid nicotine by children,” Quinlan said, arguing regulations are still too lax.

Scharman, with the West Virginia Poison Center, said the most devastating cases reported to centers have been ones in which children have gotten into liquid nicotine refills — which come in higher concentrations and higher volumes, but don't always come in child-resistant containers.

Ray Story, founder and CEO of the Tobacco Vapor Electronic Cigarette Association, said his nonprofit trade organization supports efforts like age restrictions and child-resistant packaging “so that some of these unnecessary accidents can be a thing of the past.” Furthermore, he said, he thinks there should be limits on the strength of concentrated liquid nicotine and the size of the bottles it comes in.

Story said that anytime an incident like the one in Oregon occurs, it deeply concerns him.

“But there is some responsibility of the user,” he said in an interview. “It's no different than locking your liquor cabinet or putting your laundry detergent away.”

Read more:

The facts behind e-cigarettes and their health risks

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