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SEATTLE -- Epinephrine auto-injectors (EAIs) still worked after freezing in a lab study, a researcher said here, suggesting (but not proving) that leaving one in a car parked overnight in wintertime Minneapolis would not make it unusable.

After subjecting auto-injectors to freezing temperatures for 24 hours, Julie Brown, MD, of Seattle Children's Hospital, and colleagues found no impairment in their functionality after thawing.

Brown, who presented the findings at the American College of Allergy, Asthma, & Immunology concluded that while freezing is not recommended, accidental exposure to freezing temperatures for short periods presents a low risk for malfunction.

"Since many people who live in cold climates use an EAI, we wanted to explore the effects of freezing on how an EAI functions," Brown said. For example, the devices may be left in automobile glove boxes, or become frozen during wintertime power failures.

For the study, her team took 104 same-lot pairs of EAIs and froze one of each pair for 24 hours, while the other was kept at recommended temperatures as a control.

Once the frozen devices were thawed, they and their controls were injected into meat. The meat and devices were then weighed both before and after firing and the change in meat weight and device weight were found to be similar.

The study was sufficiently powered (>95%) to conclude equivalence for both outcomes, defined as equivalent if the average difference in mass for frozen devices was within 10% of the difference for unfrozen devices.

Statistical analysis showed equivalence for both outcomes (P<0.0001) indicating frozen and thawed devices fired a similar mass of epinephrine solution compared with unfrozen devices.

Testing continued to show equivalence after controlling for device epinephrine dose (0.3 mg versus 0.15 mg) and expiration date, using two one-sided tests in a general linear model.

Allergist Anne Ellis, MD, who chairs the ACAAI Anaphylaxis Committee, told MedPage Today that the study findings should reassure people who depend on EAIs and live where temperatures frequently dip below freezing -- although the assurance isn't as complete as one might want.

"This test looked at whether freezing would affect the mechanics of an epinephrine auto-injector, but they didn't look at whether it impacted the quality of the epinephrine in the device," she said. "It's reassuring to know that it will still fire if it accidentally freezes, but it may not be delivering a full dose of [fully active] epinephrine."

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