Are Allergy Auto-Injector Needles Long Enough for Obese Patients?

For certain people with severe allergies, sometimes combined with asthma, a higher risk for anaphylaxis -- a rare allergic reaction that's a life-threatening medical emergency -- is a concern. As a safeguard, many carry a prescription epinephrine auto-injector, or EAI.

But for heavier people, particularly women, injector needles may not be long enough to deliver the medicine into the thigh muscle as intended. Instead, epinephrine may only reach the subcutaneous area -- the fatty tissue layer beneath the skin. In recent small studies, researchers used ultrasound to measure the distance from skin to muscle in different groups of patients of varying sizes. For some larger patients, that distance was longer than the length of auto-injector needles.

It's not clear whether epinephrine auto-injectors are any less effective for larger users, or if any deaths have occurred conclusively as a result. But study authors say there's cause for concern, and an advocacy group wants manufacturers to offer U.S. consumers a second adult injector choice with longer needles.

Currently Available

Anaphylaxis is triggered by some drugs, insect stings and foods such as shellfish or peanuts. Symptoms can include hives, facial swelling and flushing, breathing problems and loss of consciousness. Anaphylactic shock, caused by a precipitous drop in blood pressure, requires immediate treatment. Epinephrine is a naturally occurring chemical. It works by increasing blood pressure, relaxing breathing muscles, boosting heart function and reducing hives and swelling.

Three prescription-brand epinephrine auto-injectors are approved in the U.S. These are EpiPen (Mylan), Auvi-Q (Sanofi) and Adrenaclick (Amedra). Each comes in two forms: a half-dose version for small children (33 to 66 pounds) and a regular-dose version for anyone weighing 66 pounds or more.

Jury Still Out

"The jury is still out as to the importance of a longer needle," says Dr. Phil Lieberman, an allergist in Memphis, Tennessee. Any discussion comes with caveats, he says, because of limited available data. "The theoretical observation, supported by three very small studies in both adults and children, is that the most rapid-acting administration of epinephrine is through the mid-thigh into the muscle called the vastus lateralis," he says. Intramuscular injections are used to disperse medication quickly into the circulation. The mid-thigh muscle is the recommended location for EAI injections.

Lieberman, a member of the the American College of Allergy, Asthma and Immunology Anaphylaxis Committee, helped develop updated guidelines to be published in November, which favor intramuscular over subcutaneous injections. The Food and Drug Administration approves either subcutaneous or intramuscular injection for EAIs. Lieberman notes that, given the nature of anaphylaxis, there are no double-blind, placebo-controlled studies to compare the methods in such emergencies. That said, he adds, "The consensus of expert opinion -- not established double-blind studies -- is that the intramuscular injection into the thigh is the route of choice."

Gap in Length

In auto-injectors approved for U.S. patients, the needle length for adult versions is about 15.9 millimeters, or 0.6 inches. In a study in the October 2014 issue of Allergy, Asthma & Clinical Immunology, researchers measured skin-to-muscle depth in patients with severe food allergies. The measurement was done at the mid-thigh, the recommended site for injection.

Of 100 participants, 19 percent -- all women -- had skin-to-muscle depth beyond the length of the needle. Co-author Dr. Harold Kim, an allergist and clinical immunologist affiliated with Western University and McMaster University, in Ontario, Canada, explains what motivated the study.

"With the obesity epidemic, we were concerned that the needle for the epinephrine auto-injectors may be too short for patients, and it might not reach the muscle where we would like the drugs to get to," he says. "We believe that the drugs are much more rapidly absorbed if the drug gets into the muscle compared to the subcutaneous tissue or the fat."

"All men aren't off the hook either," says Kim, who also uses ultrasound measurements in his practice. "Some men do have too much subcutaneous tissue."

More Women

Dr. Mary Colleen Bhalla, an associate professor with Northeast Ohio Medical University, led a study using ultrasound measurement on 120 emergency room patients, published in the October 2013 issue of the American Journal of Emergency Medicine. Bhalla is also the associate research director of the emergency department at Summa Akron City Hospital.

"There are times when you see patients come in and they say they gave themselves the epinephrine injection and they didn't seem to get any better," Bhalla says. However, the epinephrine injections paramedics gave brought relief. "Paramedics actually don't use an auto-injector," she says. "They're using needle lengths that there's no way they're not getting into the muscle."

Her study found 31 percent of patients were at risk of needle length inadequacy. Women were six times as likely to be at risk, particularly if they were shorter and heavier, with higher BMIs.

Asking for Choices

Peggy Howell, public relations director for the National Association to Advance Fat Acceptance, and a U.S. News For Better blogger, is concerned about recent findings on epinephrine auto-injectors. "Skin-to-muscle depth determines whether this potentially lifesaving treatment hits its mark," she says.

Health care providers should be aware of the issue of inadequate needle length, Howell says: "Doctors need to measure their patient's skin-to-muscle depth by ultrasound before prescribing the EpiPen or Auvi-Q to their patients [who] are highly allergic and may be at risk."

In their change.org petition, NAAFA asks the makers of EpiPen (Mylan) and Auvi-Q (Sanofi) to create a version with a longer needle and possibly a larger dose of epinephrine.

Manufacturers Respond

Dr. William Daley, vice president and medical director for Auvi-Q at Sanofi, says epinephrine auto-injectors are equally effective whether used in the fat tissue or muscle.

"All EAIs are indicated [to be given] subcutaneously, which is in the fat tissue; or in the muscle," Daley says. "You can give it either way. The needle is appropriate whether you're a very small person or very large person. Whether you go into muscle or the subcutaneous tissue, you're getting the full dose."

Dosage guidelines don't change for severely obese patients, Daley says. "The standard recommendation is, you give the injection of 0.3 milligrams." He notes that all patients must seek help after using epinephrine to treat a reaction. "About 20 percent of people get a second reaction," he says. "Nothing to do with obesity or size. It's just the nature of anaphylaxis. ... And that's a critical reason why you always see two EAIs in a packet."

A statement from Nina Devlin, head of global communications for Mylan, briefly addresses the issue of weight:

"EpiPen® (epinephrine injection) Auto-Injector is approved by FDA for adult patients ?30 kg (66 lbs.) for the emergency treatment of life-threatening allergic reactions (anaphylaxis) caused by allergens, exercise, or unknown triggers; and for people who are at increased risk for anaphylaxis," the statement says. "According to the Guidelines for the Diagnosis and Management of Food Allergy in the United States, the epinephrine auto-injector is a first-line treatment for anaphylaxis regardless of weight."

New Overseas Option

Last year, Emerade, a new brand of epinephrine auto-injectors, was introduced in the U.K. Unlike U.S. brands, a larger dose is available based on body weight. And the needles are longer. The two non-junior versions have a 25 mm needle -- nearly 1 inch long.

One debate is whether those needles could be too long. "In some patients, what's called skin-to-bone-length would have that needle hit the bone," Lieberman says. While injections into bone are used in certain diseases or emergencies, he says, those are given under sterile conditions. If needed, epinephrine auto-injectors can be used through clothing, which is not a sterile field.

What You Can Do Now

Regardless of body size, for allergic people who carry prescription auto-injectors, experts recommend the following:

Call 911: "Many times a patient gets what we call a biphasic response," Lieberman says. "You get a problem -- it goes away with the first shot, then returns." The most common time lapse between the first and second allergic reaction phase is one to six hours, he says.

Keep two injector kits: The possibility of a second reaction is one reason for patients to carry two injector kits, Lieberman says. Another is that an allergic reaction may simply be too severe to respond to a single dose of epinephrine. "The third reason is that people make mistakes."

Press skin down while injecting: When patients are trained to use auto-injectors, Bhalla says, they're told, "push down as hard as you can, then inject, rather than putting it lightly on the surface of your skin."

Epinephrine is key: In a severe allergic reaction, Lieberman says, "It is clearly shown that epinephrine is the drug of choice. Nothing substitutes to prevent fatalities." Antihistamine drugs like Benadryl take too long to work, he says, although it's acceptable to use them after giving epinephrine.

Lisa Esposito is a Patient Advice reporter at U.S. News. You can follow her on Twitter, connect with her on LinkedIn or email her at lesposito@usnews.com.