By Kathryn Doyle
NEW YORK (Reuters Health) - People with serious allergies who are obese may find out in a moment of crisis their epinephrine injection needles aren't long enough to be effective, according to a new study.
"Epinephrine works best when injected into the muscle," lead author Dr. Mary Colleen Bhalla said. "When it is injected into the fat layer of the skin it takes longer to reach the blood stream."
"When a person is having a severe allergic reaction they need the medicine to work as soon as possible," she told Reuters Health.
In an allergy attack, airways constrict and may make breathing impossible. While waiting for emergency responders to arrive on the scene, the victim or a friend may use an autoinjector to deliver epinephrine, or adrenaline - a hormone that constricts blood vessels and relaxes airway muscles - into the thigh.
If the injector needle is not long enough to reach muscle tissue, the extra time the drugs take to get into the bloodstream could be the difference between life and death for people with severe allergic reactions, Bhalla, of the Summa Akron City Hospital in Ohio, said.
"A bee sting can cause death in 15 minutes," she said. "One study found that the epinephrine got in the bloodstream in an average of 8 minutes when given in the muscle, but an average of 34 minutes when given in the fat layer of the skin."
In an indirect investigation of the problem, Bhalla's team decided to measure the thickness of fat around the thighs of a random sample of patients in an emergency room and compare the measurements to the length of the longest available needle. At the time, the longest needle available was about 16 millimeters, or about two-thirds of an inch.
Of 120 emergency room patients, 31 percent had layers of fat thicker than 16 millimeters around the thigh, the usual epinephrine needle injection point. Five percent of men and 54 percent of women in the sample fell into this category, according to the researchers' report in the American Journal of Emergency Medicine.
More than half of the people studied were obese.
The results are still hypothetical, since the researchers didn't go as far as trying the injectors on people having allergy attacks to see if they would be effective.
An injector with a 25 millimeter needle - about an inch - has been approved and will be available in late 2013 in the UK, Germany and Sweden, which would help solve the problem in the U.S., Bhalla said.
"In our study we found that we would need a needle length of 18mm to get the drug in the muscle in 95 percent of men, however we found that we would need a needle length of 35mm to get the drug in the muscle of 95 percent of women," she said.
But 35 millimeter needles would hit bone for some people and could be dangerous. A wider variety of needle sizes or an autoinjector that automatically adjusts needle length on insertion might be the best solution, she said.
Patients should always keep their injector close and use it s soon as they realize they have been exposed to an allergen, and call emergency medical services as soon as possible, she said. Professionals have better ways of delivering the necessary drugs.
"This study and several others suggest that the needle length of the autoinjectors may be too short to reach muscle in people with more body fat in the leg," Dr. Scott Sicherer said. "This is an important concern."
Sicherer is a professor of pediatrics and a researcher at the Jaffe Food Allergy Institute at Mount Sinai in New York, and was not involved in the study.
"Since the injectors forcefully spray the medicine beyond the tip of the needle, and there are insufficient direct studies of how the medications behave in people of different body sizes, the studies like this one looking simply at the anatomy of the leg have practical limitations," he said. "However, an important question is being raised that warrants more study."
(This story has been refiled to change headline to remove reference to brand-name device.)
SOURCE: http://bit.ly/16KS1ve American Journal of Emergency Medicine, online October 4, 2013.