FDA resumes review process for ultrasound contrast agents

New clinical trials seek to broaden agents' utility

The Food and Drug Administration's review of ultrasound contrast agents is back on track following the FDA's decision last month to review all products intended for diagnostic ultrasound as drugs. The U.S. District Court in Washington, DC, has lifted the preliminary injunction that had barred the FDA from continuing any approval or review procedures on four ultrasound contrast agents.

The injunction had prohibited any review by the FDA until 10 days after the agency had responded to the citizen's petitions filed by Sonus Pharmaceuticals, Bracco, ImaRx Pharmaceutical, and ImaRx marketing partner Du Pont Merck. The district court lifted the injunction on Aug. 5, a week after FDA Deputy Commissioner Dr. Michael Friedman ruled that the FDA would regulate all ultrasound contrast agents as drugs under the Center for Drug Evaluation and Research (SCAN 8/6/97).

With the regulatory process under way again, the next legal fight will be over patents. On Aug. 1, MBI and its marketing partner Mallinckrodt filed suit against Sonus, Nycomed, ImaRx and Du Pont Merck, and Bracco (SCAN 8/6/97). MBI and Mallinckrodt are charging that their competitors' patents are invalid.

Meanwhile, clinical trials for ultrasound contrast agents are continuing. MBI has completed patient enrollment in two phase II trials of Optison for use with echocardiography. The studies of myocardial perfusion will be the next indication for Optison, according to the company.

The first study, to be conducted at five U.S. sites, will compare the ability of exercise stress echo using Optison with SPECT nuclear imaging for identifying resting and stress-induced myocardial perfusion. The second study will evaluate the ability of Optison-enhanced echocardiography performed during balloon angioplasty to demonstrate acute myocardial perfusion defects, acute reperfusion, and collateral perfusion, according to MBI. The trial will be conducted at one site in the U.K.

Sonus, on the other hand, has begun a phase III clinical trial investigating the use of EchoGen in transrectal ultrasonography of the prostate. The study is designed to show the ability of EchoGen to aid in the diagnosis of prostate cancer by assisting in the identification of biopsy sites and facilitating the visualization of normal and abnormal blood flow patterns, structures, masses, and lesions, according to Sonus. Ten locations in the U.S., Europe, and Canada will participate in the trial.