Cladribine underdosing in hairy-cell leukemia: a cause for apparent response failure.

While chemotherapy overdose is often readily discovered, underdosing errors are seldom appreciated. We report two patients with hairy-cell leukemia who apparently failed to respond to cladribine administered by continuous portable pump infusion. It was determined that both patients received one-seventh of the prescribed dose, although the orders were written correctly. The errors resulted in the administration of 1 day's dose over I week. The use of 7-day portable pump infusion therapy for cladribine can be associated with misdosing, and is an occult cause of apparent failure to respond in hairy-cell leukemia.