- Off previous therapy ≥3 weeks prior to first study drug administration with full recovery from any previous toxicities, except 1) hydroxyurea single agent of in combination (e.g. + 6-Mercaptopurine [6MP]) to control hyperleukocytosis, which should be stopped for ≥48 hours, and 2) rituximab, which should be stopped for ≥3 weeks.