Disclosed are compositions and methods for treating a disease, such as infection, pain, or inflammation, by using the compositions. Particularly, disclosed is a method of treating oral pain, wherein, the above-described compositions are applied to the oral mucosa; the compositions undergo in-situ gelation, optimal adhesion to the oral mucosa, controlled erosion and controlled release of the active ingredient, i.e., benzocaine, which provides a superior degree of pain relief or analgesia for an extended period of time.