LOS ANGELES (FRONTLINE MEDICAL NEWS) – For about half of children under 15 kg, pediatric epinephrine autoinjector needles are too long – they’re likely to hit the femur.

If the drug is deposited at the periosteum, it won’t be absorbed properly. If the needle delivers it to the bone marrow, the results could be disastrous.

“I’ve had three patients where the needle came back bent, so this happens,” said Dr. Harold Kim, an allergist in Kitchener, Ont. “Fortunately, there’s a fairly simple workaround. I ask parents to squeeze the [thigh] muscle before they give the shot, so that the muscle doesn’t compress. If the muscle doesn’t compress, you won’t hit bone, and the kid is going to be fine. Parents are really grateful” to learn this, but “they have to be careful not to inject their fingers.”

The findings come from Dr. Kim’s ultrasound study of thigh tissue thickness in 53 children weighing 7.5-15 kg. He and his colleagues found that with 10 pounds of pressure to simulate autoinjector deployment, the mean skin-to-bone distance was 13.3 mm, plus or minus 2.1 mm ( J Allergy Clin Immunol. 2016 Feb. doi: 10.1016/j.jaci.2015.12.1167 ).

The needle length for EpiPen Jr is 12.7 mm, which was long enough to strike bone in 43% of the subjects.

“Epinephrine autoinjectors should be the mainstay of treatment for anaphylaxis, but our data suggest that the optimal needle length” for patients 7.5-15 kg “should be shorter than the needle length in current, commercially available” products. “There may be some modifications that need to be made in the way they are given. I actually ultrasound all the kids in my clinic to see if there will be problems,” Dr. Kim said at the American Academy of Allergy, Asthma, and Immunology annual meeting.

The study was done with an ultrasound probe in a housing that mimicked the footprint of Sanofi’s Auvi-Q, which is no longer on the U.S. and Canadian markets. If anything, the problem would be worse with EpiPen Jr because of its smaller footprint, Dr. Kim said.

On average, the subjects were 20 months old and 11 kg. Just over half were boys, and about 80% were white. The mean height was 79 cm and mean body mass index 19 kg/m2. About 60% of the subjects had injectors because of food allergies. Both transverse and longitudinal images of thigh tissue were used in the study, and distances were read by a blinded ultrasound expert.

Dr. Kim and his colleagues became interested after finding that needles may actually be too short to reach muscle in obese patients. While working on that issue, however, they also discovered “that 30% of kids less than 15 kg were at risk of the needle hitting the bone. We were surprised by those findings,” so looked into them further, he said.

EpiPen Jr is off label for children under 15 kg, but still often prescribed for them.

Sanofi funded the work. Dr. Kim is an advisor for the company, as well as for Pfizer, maker of EpiPen.


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