Fasting is invalidated; because the anus is one of the considered openings in Sharia, so fasting is invalidated if something enters it. It should be used before dawn or after breaking the fast. However, if one is compelled to use it, it is permissible for him to do so, and he should continue to refrain for the rest of the day out of respect for Ramadan, and he must make up that day. As mentioned in Badā'iʿ al-Ṣanāʾiʿ 2: 93.