New aspects on the pharmacokinetics of mitoxantrone and its two major metabolites

In spite of its broad clinical application in the treatment of malignant disorders, the pharmacokinetics of mitoxantrone are still not fully understood and warrant further investigation. Information is also limited about interindividual differences in the plasma AUC infinity (area-under-the-curve concentration to time infinity) and renal elimination of mitoxantrone and its main metabolites, mono- and dicarboxylic acid. In the present study, the plasma concentration of mitoxantrone was measured by HPLC during 120 h after the end of a 30-min infusion of 10 mg/m2 in 18 patients undergoing combination therapy with mitoxantrone and high-dose cytosine arabinoside for acute myeloid leukemia. Plasma kinetics and renal elimination of mono- and dicarboxylic acid were analyzed in addition in eight of these patients, and in five cases with chronic lymphocytic leukemia receiving a 30-min infusion of 5 mg/m2 mitoxantrone weekly for 3 consecutive weeks. Fitting the results to a three compartment model, a substantial interindividual variation was observed for plasma and urine pharmacokinetics. Plasma AUC infinity for mitoxantrone differed approximately 13-fold between individual patients and varied between 80-1030 ngh/ml. The corresponding values for mono- and dicarboxylic acid ranged from 23-147 ngh/ml and 51-471 ngh/ml, respectively. The median terminal half-life for mitoxantrone was similar to that of the mono- and dicarboxylic acid and was 75 h. Cumulative renal elimination ranged from 670-1950 micrograms for mitoxantrone, from 366-852 micrograms for monocarboxylic acid, and from 792-3420 micrograms for dicarboxylic acid. Renal clearance of mitoxantrone reached a median level of 69 ml/min and for the total plasma clearance a median of 1136 ml/min was found. The corresponding values for the mono- and dicarboxymetabolites were 57 and 67 ml/min. In contrast to the great interindividual differences in pharmacokinetic results, a low intraindividual variability was observed upon repeated determinations of renal elimination of mitoxantrone and its metabolites at weekly intervals in five patients. These data provide new insights into the pharmacokinetic of mitoxantrone and its main metabolites revealing substantial differences in drug metabolism and elimination between individual patients. Further studies are needed to explore the potential impact on response and/or toxicity and the requirement of a pharmacokinetic directed adjustment of drug dosage in clinical trials.