The TEN study: time epinephrine needs to reach muscle

An epinephrine autoinjector (EAI) is designed to deliver epinephrine into the vastus lateralis muscle. Several studies have demonstrated both patient and physician difficulties in correctly using EAIs, specifically premature removal of the device from the thigh.

To evaluate the correlation between duration of injection with an EAI and amount of epinephrine absorbed into muscle tissue.

Twenty-one EAI devices (0.3 mL) were used to determine the amount of epinephrine injected into marbleized beef during 7 time periods. A digital scale was used to record preinjection and postinjection weights of EAIs and beef. The weight difference between the preinjection and postinjection periods of the EAIs was used to calculate the total amount of epinephrine released and available for absorption into the marbleized beef. The difference between the preinjection and postinjection beef weight was used to determine the amount of epinephrine absorbed into the meat.

The correlation with duration of injection for both the amount of epinephrine absorbed and released was 0.321 (P = .48). At all intervals, 95.9% or more of epinephrine was absorbed into the marbleized beef. The correlation with duration of injection and percent of epinephrine absorbed was 0.464 (P = .29). There were no time periods that were significantly different from the percentage of epinephrine absorbed by the marbleized beef at 10 seconds (analysis of variance P = .16).

No linear relationship between time and amount of epinephrine injected or absorbed into muscle tissue was demonstrated. These data suggest that holding the device in place for 1 second is as effective as 10 seconds.