According to the Everyday Health website, milk should not be consumed while on tetracyclines, a particular family of antibiotics. The calcium present in the milk binds with tetracyclines, preventing absorption of the antibiotics in the gut.
Oral antibiotics are only effective when absorbed from the gastrointestinal tract and delivered to the infected region of the body through the bloodstream. The relative acidity of the stomach and the nutrients present in the stomach are among the factors influencing proper absorption of antibiotics. According to Everyday Health, food helps with the absorption of some antibiotics, but for the most part has no effect or decreases absorption. A person should always take antibiotics as directed to by a doctor or pharmacist.