Occasionally, when generating a level 6+ spellbook, set its opoisoned flag to true. You get “The book was coated in contact poison!” not as a random spellbook reading failure effect, but when you try to read a book whose opoisoned is set to true. Triggering the contact poison usually (but not always) clears the opoisoned flag, so it won’t be poisoned if you try to read it again.

Dipping a poisoned spellbook in any healing potion will neutralize the poison and use up the potion. Possibly, dipping it in a potion of sickness will poison the book, though this would be useless unless monsters read spellbooks.