Epinephrine concentrations after injection decrease with greater BMI
Click Here to Manage Email Alerts
Key takeaways:
- Epinephrine may be given via intramuscular and subcutaneous injections.
- Intramuscular and subcutaneous injections use different needle lengths and gauges.
- Injections must reach the vastus lateralis.
ANAHEIM, Calif. — There was a significant negative relationship between epinephrine exposure via injection and BMI, according to a presentation at the American College of Allergy, Asthma & Immunology Annual Scientific Meeting.
“Epinephrine is the standard of care for the treatment of severe allergic reactions,” John Oppenheimer, MD, FACAAI, clinical professor of medicine at UMDNJ Rutgers, said during the presentation.
Many providers rely on intramuscular (IM) injections of epinephrine, continued Oppenheimer, who also is a member of the Healio Asthma/Allergy Peer Perspective Board, but needle length may have an impact on how much epinephrine is absorbed in patients with high BMI.
“The goal of IM is to put it in the vastus lateralis,” Oppenheimer said.
Oppenheimer and his colleagues analyzed five studies examining the pharmacodynamics and pharmacokinetics of epinephrine administered via IM, subcutaneous and autoinjector (EpiPen; Mylan/Viatris) injections as well as by neffy (ARS Pharma) nasal spray in various quantities and frequencies.
“Remember that the applicator length may be different,” Oppenheimer said.
For example, Oppenheimer said, subcutaneous 0.3 mg doses of epinephrine use a 25-gauge needle that is five-eighths of an inch long. Intramuscular 0.3 mg doses use a 21- or 22-gauge needle that is 1 inch long.
Three studies included healthy volunteers, and two studies included patients with seasonal allergies, with a total of 220 participants.
“This is by far the largest database that we can look at with regard to the impact of IM and body weight,” Oppenheimer said.
The researchers took blood samples before dosing and up to 360 or 480 minutes after dosing. Also, the researchers used liquid chromatography-mass spectrometry and mass spectrometry.
Additionally, the researchers calculated individual pharmacokinetic parameters with concentration-time data using noncompartmental methods, with linear regression analysis of the natural logs of maximum concentration (Cmax) and area under the curve for 0 to 240 minutes (AUC0-240 min) vs. BMI.
As body weight increased, Cmax decreased significantly with single doses of 0.3 mg of epinephrine administered subcutaneously (slope = –0.06479; P = .023) and nonsignificantly with single doses of 0.3 mg of epinephrine administered intramuscularly (slope = –0.02548) and double doses of 0.3 mg of epinephrine administered intramuscularly (slope = –0.03884).
This inverse relationship between body weight and epinephrine exposure probably is related to the increased likelihood of unintentional subcutaneous injection, Oppenheimer said, or never reaching the vastus lateralis in heavier patients.
As a result, he continued, physicians may need to decide whether they use a subcutaneous or an intramuscular dose of epinephrine when they have a patient with high BMI.
“This is, again, really important,” Oppenheimer said, “because it helps us guide optimization of epinephrine as we talk about anaphylaxis guidelines.”