A delivery apparatus useful for infusing a therapeutic agent into a body lumen, the apparatus including a lumenal body defining at least one infusion port for infusing the therapeutic agent into the body lumen, and a sensing element which is distal of the at least one infusion port and adapted to sense the amount of infused therapeutic agent or any compound derived therefrom in the body lumen. Another embodiment of the apparatus includes a lumenal body defining at least one infusion port for infusing the therapeutic agent into the body lumen, and a filtration element which is distal of the at least one infusion port and adapted to deliver a reaction agent which may react with the therapeutic agent in the body lumen. A sensing element may be provided distal of the filtration element for sensing the amount of infused therapeutic agent or compounds derived therefrom in the body lumen.