Alex had ditched the demonic beast mount about a kilometer or two back in a hidden Grove, which more than explains his and Khan's current sprawled out and crawling forms through the underbrush of the forest.
Now normally such an action was asking for a one way ticket to the land of the dead, however because Alex already had Xeron, the idea of dying to poison would probably be an alien concept to him, not unless it's a poison specifically engineered to kill him.
