Dairy products contain more protein and calcium ions. Calcium ions can form complexes or chelates with tetracyclines and isoniazid, which are not easily absorbed by gastrointestinal tract and weaken antibacterial effect; Calcium ion reacts with phosphate and sulfate to produce calcium phosphate and calcium sulfate precipitate with less solubility, which reduces the curative effect.
So if you are taking medicine, you'd better take it after you get well!