Q about original Half-Life: give_item cheat

In the original Half-Life, enabling cheat codes allowed you to give yourself items. The list of items you could give yourself included a couple of things that didn’t seem to be implemented in the final released version of the game: Airtaink, Antidote, and Security for example. Does anyone know the story about what these items were originally intended to do? Have any mods implemented them? And also, why can some items be spawned anywhere, but others (such as Healthkit) can only be spawned if the current map already contains one?