I say, and with God's success: Whoever applies medicine to a wound that prevents water from reaching it, like an ointment or the like, must pass water over it. If he passes water over the medicine and then the medicine falls off: if the fall was due to healing, he should wash the area if he is not in a state of ritual impurity. If he is in a state of ritual impurity, he should perform a complete ablution. If he is praying and the medicine falls off due to healing, he must repeat the prayer. If the fall was not due to healing, he is not required to wash the area. Refer to: Sharh Al-Wiqayah p.119, and Nihayat Al-Murad p.401, and God knows best.