Background: Doxorubicin (DOX) is an effective treatment for many cancers across the age spectrum, but its therapeutic potential is limited because of dose-dependent relation to both progressive and irreversible cardiomyopathy leading to congestive heart failure. While decreases in cardiotoxicity have been reported with liposomal doxorubicin, the long-term cardiac effects are not known. Orotate salts of cytotoxic drugs have been shown to confer antitumor effects with a better safety profile than unconverted drug, and therefore may offer an improved approach to cancer treatment. Materials and Methods: Male, athymic NCr-nu/nu mice with subcutaneously implanted CAKI-1 human renal tumor xenografts were treated with DOX and its orotate salt (DOX-O) to evaluate antitumor activity, measured by median tumor mass doubling time and tumor weight. Nontumored male, athymic NCr-nu/nu mice were treated with DOX, DOX-O and liposomal doxorubicin formulations to determine DOX concentration in liver and heart; and to evaluate their effect on body weight. Non-tumored female, athymic NCr-nu/nu mice were treated with daunorubicin and daunorubicin orotate to evaluate tolerance. Results: DOX and DOX-O exhibited significant, similar levels of antitumor activity. Mice treated with DOX-O had a lower percentage body weight loss. In the animals treated with DOX, DOX-O, or liposomal doxorubicin, liposomal doxorubicin was associated with the lowest percentage of body weight loss, but the highest concentration of DOX in heart. In daunorubicin tolerance experiments, animals showed a better tolerance for daunorubicin orotate as measured by a smaller percentage change in body weight. Conclusions: DOX-O is effective as an antitumor therapy and may offer a less toxic alternative to DOX for maintaining therapy. The lower percentage of body weight loss in animals treated with DOX-O and daunorubicin orotate is a measure of improved tolerance and may translate into better patient outcomes.