13. Patients who have received the following types of prior or concurrent therapy, or who have not recovered from the toxic effects of such therapy: 1) investigational drugs less than 4 weeks prior to entry on this study. 2) intrathecal chemotherapy within 2 weeks prior to entry into this study. 3) systemic cytotoxic chemotherapy within 4 weeks prior (6 weeks for nitrosourea or mitomycin-C or 2 weeks for vincristine) to entry on this study. 4) radiation therapy within 2 weeks prior to entry on this study. 5) any medication known to cause QT interval prolongation.