Adrenaline concentration in epinephrine autoinjectors (EAIs) was significantly decreased following a single 12-hour-long heat exposure inside a parked car on a summer day, according to results of a real-life pilot study.

In order to determine the effect of heat exposure on the concentration of adrenaline in EAIs, the study authors placed nine 0.3mg EpiPen Senior EAIs inside a parked car from 8:30 AM until 8:30 PM on a summer day. The EAIs were placed in 3 zones of the car with no direct sun exposure – the glove compartment, a shelf under the rear window, and the trunk. As a control, 3 EAIs were placed inside a dark, air-conditioned room, constantly measured at 68°F. Epinephrine concentration was measured using high-performance liquid chromatography (HPLC) with a photodiode-array detector.

On the day of the study, the outdoor temperature was reported to range from 75.2°F to 89.6°F and the peak temperature inside of the cabin of the car was recorded as 143.6°F. Inspection of the EAIs following the experiment showed no discoloration, cloudiness, or visible particles and delivery mechanisms all functioned properly. The study authors noted, however, that unlike the other devices, the EAIs placed in the glove compartment were “noticeably warmer to touch.” 

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The study authors reported, “HPLC analyses revealed a 3.3%, 13.3%, and 14.33% reduction in epinephrine concentration in samples placed in the trunk, cabin, and glove compartment, respectively.” Because most people consider the glovebox to be the safest storage space for first aid kits, it is particularly concerning that the most significant reduction in epinephrine concentration was observed for EAIs placed in the glovebox. It is also important to note that the appearance of the solution did not visibly change despite observing a reduction in epinephrine concentration.

“On the basis of our observations, we can hypothesize that even a single exposure to excessive heat in a car can decrease epinephrine concentration in an autoinjector below the recommended dosage,” the study authors concluded. They added, “Although the decreases measured after this 1-day heat exposure would be unlikely to affect the effectiveness of the administered dose, further studies are needed to evaluate if such degradation is progressive or cumulative, which could lead to clinically ineffective underdosing.”


Lacwik P, Bialas AJ, Wielanek M, Sklodowska M, Kupczyk M, Gorski P, Kuna Piotr. Single, short-time exposure to heat in a car during sunny day can decrease epinephrine concentration in autoinjectors: a real-life pilot study. The Journal of Allergy and Clinical Immunology. doi: 10.1016/j.jaip.2018.10.027.

This article originally appeared on MPR