The Relation between the Initial Type of Schedule Used to Administer Doxorubicin and Long-Term Doxorubicin Cardiotoxicity

Abstract

Background: As more patients survive cancer chemotherapy, problems associated with the late complications of therapy have become increasingly apparent; late doxorubicin cardio-myopathy being one of the most pressing. The relationship between initial dose, schedule employed, and etiology are still not well defined. This study attempts to clarify some of these issues. Methods: Patients receiving large total doses of doxorubicin by schedules designed to minimize peak drug levels were monitored in regard to their cardiac status for up to 31 years following completion of doxorubicin therapy. A computer program predicting the amount of doxorubicin retained by the heart vs. schedules employed was devised with the predictions of the computer program being compared to the clinical findings. Results: 1365 patients receiving doses of doxorubicin greater than 610 mgm./M 2 were monitored for up to 31 years following completion of such therapy. No patient developed unequivocal clinical and pathologic evidence of a doxorubicin related cardiomyopathy. Knowing that human cardio-myocytes contain enzymes capable of neutralizing doxorubicin, a computer program predicted that by increasing their efficiency, the schedules employed substantially l decreased the relative amount of drug retained by the heart, findings compatible with both animal experiments and clinical results. Conclusions: administration of doxorubicin by schedules in which peak plasma levels of drug were minimized resulted in marked decreases in both acute and long-term cardiac toxicity; believed to be due to potentiation of myocardial enzymes capable of inactivating the drug.