Something like "Some threshold of official approval/proven safety has not been met, but we'll break the rule this time and give it to them anyway since they're very sick and we don't have any other options."
It means that the FDA will make an exception for unapproved drugs if the other option is to just let the person die or suffer needlessly. For example, it is usually used in cases where the patient will die anyways and they need something to keep them comfortable. (palliative care) This is how a lot of cancer patients got exceptions for marijuana use before medical legalization.
It refers to a special kind of use for medication that is not approved.