Studies of hydroxyurea administered by continuous infusion: toxicity, pharmacokinetics, and cell synchronization.

Hydroxyurea was administered by means of two schedules designed to provide continuous 72-hour exposure of tumor cells to therapeutic drug levels. Toxicity and pharmacokinetics were determined for both an oral pulse dose schedule (every 4 hours x 18 doses) and continuous intravenous (IV) infusion for 72 hours. The maximal tolerated dose (MTD) was 800 mg/m2 every 4 hours for the oral route and 3.0 mg/m2/min x 72 hours for IV infusion. Granulocytopenia was dose-limiting for both schedules and correlated well with plasma-HU levels. Serial sampling of normal bone marrow (10 patients) and tumor tissue (3 patients) showed a modest degree of synchronization induced by continuous IV infusion of hydroxyurea. Interindividual pharmacokinetic variations severely limit the usefulness of the oral pulse schedule as a potential means of synchronizing cells. Hydroxyurea administered by continuous IV infusion may be useful as a synchronizing agent in humans.