It does not belong to any special class of drugs. It's a very specific drug that has very specific drug action.
It block cortisol synthesis by blocking 11 beta hydroxylase.
It's used in the diagnosis of adrenal insufficiency.
You give the patient Metyrapone at night after you measure ACTH level and 11 deoxycortisol.
If the patient is having an intact ACTH response to (lowered cortisol) then the next morning you should see increased levels of ACTH and 11 deoxycortisol as the patient has increase his/her ACTH level but it could not make cortisol as the 11 hydroxylase enzyme is being blocked by metyrapone.