The present invention provides methods and formulations for optimizing the anti-cancer and anti-HIV activities of a camptothecin drug, including camptothecin and its related analogs including 9-aminocamptothecin and 9-nitrocamptothecin. The invention involves methodologies and formulations that limit human serum albumin-mediated reduction of the anti-cancer and anti-HIV effects of the camptothecins, and the methods and formulations provide combination therapies in which binding of the camptothecin agent to human serum albumin can be modulated by the administration of a competing agent that also binds human serum albumin. Reduced camptothecin drug binding to human serum albumin can result in elevated camptothecin free drug levels and thus improve the effectiveness of treatment regimens involving these drugs. Further agents such as methotrexate and AZT can also be used in cancer and HIV-positive patients employing camptothecin drugs.