acoustically active lipospheres containing paclitaxel a new therapeutic ultrasound contrast agent rationale and objectives paclitaxelcarrying lipospheres mrx552 were developed and evaluated as a new ultrasound contrast agent for chemotherapeutic drug deliverymethods paclitaxel was suspended in soybean oil and added to an aqueous suspension of phospholipids in vials the headspace of the vials was replaced with perfluorobutane gas the vials were sealed and they were agitated at 4200 rpm on a shaking device the resulting lipospheres containing paclitaxel were studied for concentration size acute toxicity in mice and acoustic activity and drug release with ultrasound lipospheres containing sudan black dye were produced to demonstrate the acoustically active liposphere aalultrasound release conceptresults acoustically active lipospheres containing paclitaxel had a mean particle count of approximately 1 x 109 particles per ml and a mean size of 29 microns acute toxicity studies in mice showed a 10fold reduction in toxicity for paclitaxel in aals compared with free paclitaxel the aals reflected ultrasound as a contrast agent increasing amounts of ultrasound energy selectively ruptured the aals and released the paclitaxelconclusions acoustically active lipospheres represent a new class of acoustically active drug delivery vehicles future studies will assess efficacy of aals for ultrasoundmediated drug delivery