An apparatus for delivering ultrasound energy and a drug solution to a treatment site in a vessel is disclosed. The apparatus includes an elongate, hollow sheath having a distal opening and an energy delivery section at least partially constructed from a material that transmits ultrasound energy. The apparatus also includes a drug delivery lumen positioned along at least a portion of the sheath, the drug delivery lumen having at least one drug delivery port within the energy delivery section. The apparatus further includes an elongate body having an ultrasound element, the elongate body configured to be movably positioned within the sheath, such that ultrasonic energy can be transmitted from the ultrasound element through the energy delivery section.