- Patients must have recovered from the toxic effects of prior therapy: 4 weeks from prior cytotoxic therapy and/or at least 2 weeks from vincristine, 6 weeks from nitrosoureas, 3 weeks from procarbazine administration, and 1 week for non-cytotoxic agents, e.g., interferon, tamoxifen, thalidomide, cis-retinoic acid, etc. (radiosensitizer does not count), 4 weeks for experimental biologic agents (epidermal growth factor receptor [EGFR] inhibitors, etc) and 7 weeks from Gliadel implantation