Keeping Drugs Stable Without Refrigeration

A spoonful of sugar may help the medicine go down, but it may take only a thin coating of freeze-dried sugar to keep insulin, vaccines and other heat-sensitive, protein-based drugs working reliably even when stored at room temperature and above. Widespread availability of stable, room-temperature therapeutic proteins and vaccines would lower the cost and increase the convenience of these drugs, and could dramatically improve distribution in areas of developing nations where refrigeration may be limited.

New measurements taken by National Institute of Standards and Technology (NIST) scientists and published in the June edition of Biophysical Journal show that rapidly solidified sugars preserve such proteins best when they suppress tiny, molecular motions lasting a nanosecond or less. NIST scientists Christopher Soles and Marcus Cicerone used instruments at the NIST Center for Neutron Research to help them view nanoscale molecular motions of sugar mixtures that were designed to encase proteins. They found a striking correlation between sugar mixtures that provide unusually good protein stabilization and a suppression of very fast motions in the sugars.

Scientists have known for more than a decade that "glassy" sugars can preserve medicines by encasing the proteins in a protective coating. The NIST measurements show that tiny molecular "wiggling" that facilitates protein degradation occurs at time and length scales smaller than once thought to matter. They found that diluting sugars that become "glassy" at a relatively high temperature with the right amount of glycerol formed a stiffer material, further restricting the protein's movement. It's as though the sugar glove is now made of cement instead of cloth, says Cicerone.