While protamine is effective in reversing the blood-thinning properties of heparin, recent studies have shown that its use can cause changes in blood pressure which have been linked to increased mortality in some patients. In addition to its negative effects on blood pressure, protamine can also depress heart function, activate certain immune responses, and lead to pulmonary hypertension, the researchers said. However, they emphasized, the drawbacks of protamine do not compromise the overall success of heart bypass surgery, and patients should not be overly concerned by those drawbacks.
The latest candidate alternative to protamine is heparinase I, a compound naturally produced by Flavobacterium heparinum, a bacterium commonly found in soil and water. The bacterial enzyme from which heparinase I is derived deactivates heparin through a mechanism different than protamine.
However, the current Phase IIB/IIIA safety and efficacy trial conducted at 47 sites in the U.S, Canada and Germany, was halted early because patients receiving heparinase I had higher incidences of negative side effects, such as bleeding and infections. The trial was halted after 167 of a planned 600 patients were enrolled.
The results of the trial were published in the August, 2005, issue of the journal Anesthesiology.
"The trial was designed to determine if this new drug could work as well as protamine without its known side effects," said Mark Stafford-Smith, M.D., Duke cardiovascular anesthesiologist and lead author of the study. "However, after reviewing the safety profiles during the trial, the data safety monitoring board decided to
Contact: Richard Merritt
Duke University Medical Center