A study of temperature control in different designs of emergency drug transport bags

We investigated whether low melting point phase-change waxes could be incorporated into emergency drug transport bags to attenuate the known temperature extremes their contents can be exposed to. We exposed two custom-made hollow-walled drug containers placed within a pair of drug transport bags to three day/night cycles including periods of direct radiant sunlight. The wall cavities of one contained air, whereas those of the other contained a paraffin wax (melting point of 44-46 °C) with a high latent heat of fusion (until fully melted, its temperature does not increase further). We collected 25,920 temperature datasets at six locations. We found that 97.8% and 84.7% of ampoule temperatures within the wax and air cavity containers, respectively, were within a target range of 15-40 °C over the study duration (Levene statistic W = 4279.1; Levene's test for equality of variance, p < 0.001). Ampoule temperatures in the wax cavity container only exceeded 40 °C for 1.7% of the time. Even when they did so, their temperature was attenuated to 40.3 °C, despite an ambient air temperature of > 40 °C for 6.4% of the time (peak 46.9 °C) and a bag surface temperature of > 40 °C for 17.2% of the time (peak 64.4 °C). In contrast, the ampoule temperature in the air cavity container exceeded 40 °C for 17.1% of the time (peak 54.1 °C). The latent heat of fusion of phase-change materials may be exploited in the design of drug transport bags to mitigate any temperature changes in the drugs stored within them.