Prescriptions in the UK contain doxycycline as doxycycline hyclate. They are also listed as containing lactose.
Why is the lactose helpful?
Lactose is a disaccharide sugar found in milk. Many tablets contain lactose. It is not an active ingredient but simply a filler and is chosen because it has excellent compressibility properties and is biologically safe. It can also be used to form the powder in dry powder inhalers.
While people who have a true allergy to lactose should not use tablets that contain it, there is not usually enough lactose to cause problems for people who have lactose intolerance.