Effect of (2"R)-4'-O-tetrahydropyranyladriamycin, a new antitumor antibiotic, on the bone marrow function of rabbits. (2) Repeated intravenous injections

(2'R)-4'-O-Tetrahydropyranyladriamycin-HCl (THP), a new antitumor antibiotic, was intravenously injected to New Zealand White rabbits at a dose of 2.5 mg/kg every 2 weeks for 6 weeks (3 courses) or at a dose of 0.5 mg/kg/day daily for the first 5 days of a 2-week course for 6 weeks (3 courses). The total dose was 7.5 mg/kg in both dosing schedules. The peripheral leucocyte and erythrocyte counts decreased. The leucocyte count decreased to 57% of the initial count on Day 3 in the first course and then increased gradually. The decrease was smaller in the divided dosing schedule than the single dosing. The nucleated cells, especially immatured myelocytes and erythroids reduced remarkably. Subsequently the matured myelocyte ratio in bone marrow cell constituents increased and the M/E ratio increased. These changes were observed on Day 3 and reverted by Day 9 in each course. The divided dosing schedule resulted in a higher nadir. All the changes in the peripheral blood and the bone marrow reverted even after the 3 course-treatment.