I need to store pure phenytoin sodium powder at -20C to increase the shelf life. The supplier in not clear if this is OK. It is hygroscopic but it will be desiccated and warmed to room temp before each opening.

Thanks for any help

According to this site: PHENYTOIN SODIUM 100mg TABLETS; PHENYTOIN SODIUM CAPSULES (http://home.intekom.com/pharm/lennon/phenyton.html)


STORAGE DIRECTIONS:
Store below 25°C.
Store in airtight container.
KEEP OUT OF REACH OF CHILDREN.