The anti-rejection drugs that keep people alive after a heart transplant also increase the threat of potentially fatal blood clots. But a University of Maryland Medical Center study finds that one popular anti-rejection drug poses less risk of clotting in heart transplant patients than another commonly used medicine. Results of the study are published The Journal of Heart and Lung Transplantation.
"Our findings showed that patients who were on the anti-rejection medication FK506 had a significantly lower risk of forming clots than patients on the drug cyclosporine," says Ronald Fruedenberger, M.D., director of cardiac transplantation at the University of Maryland Medical Center and assistant professor of medicine at the University of Maryland School of Medicine. "This is an important finding that needs further research."
The study included 17 patients who had received a heart transplant and were taking either FK506 or cyclosporine, along with two other anti-rejection medications. For the study, blood from the patients was circulated through a perfusion machine to simulate what happens inside of blood vessels. The machine contained part of a pig's aorta, which is similar in size and function to a human aorta.
"When we looked at how much clotting was left on the sides of the artery taken from the machine, we found that there was 60 percent less clots among patients taking FK506 than among the patients taking cyclosporine," says Dr. Freudenberger. "This finding has important implications for understanding the development of coronary disease after a transplant and may improve the outlook for heart transplant patients."
Clotting is a normal response inside a blood vessel wall that has been injured. However, blood clots that form when a blood vessel wall is intact may eventually grow to block the vessel, preventing oxygen from reaching the organs supplied by that artery. Blood clots that form inside major blood vessels leading to the heart or brain can cause heart attack, stroke or death.
In heart transplant patients, there is an increased likelihood that blood clots will form as a result of the anti-rejection medication patients need to take.
"Previous studies of cyclosporine have revealed that it has a tendency to cause blood clots. This study is the first to look at FK506's propensity to form clots and the first to compare it to another anti-rejection medication," he says.
The University of Maryland Medical Center worked jointly with researchers at the Mount Sinai Medical Center in New York on this study. The study is published in the December 1999 issue of The Journal of Heart and Lung Transplantation.
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