Before a Catholic exorcism ritual, all participants must be confessed and absolved of their sins, and then take communion. Otherwise the demon can use their unconfessed sins as a weak spot or their spiritual isolation from the Church and from Christ (communion is affirming the Catholic as a member of the body of the Church) in order to attack them. For a demon as powerful as Pazuzu is supposed to be, that would be critical.
Chas says that Constantine "cast" a demon to save himself. Constantine also uses the word in the context of demons during the series. This is wrong, and is a basic misunderstanding of how Kabbalistic and Enochian magic is "supposed" to actually work. It's correct to say that magical spells are cast, but when a supernatural entity such as the demon Pazuzu already exists and is brought to the magician's location - usually from a spiritual plane and against its will - this is not "casting a spell." The magician probably will cast spells of binding and defence to hold the demon safely and prevent it attacking him, but the act of calling forth a demon is correctly called a "summoning."