Idarubicin metabolism and pharmacokinetics after intravenous and oral administration in cancer patients: a crossover study

Summary

The pharmacokinetics and metabolism of 4-demethoxydaunorubicin (idarubicin, IDA) were studied in 21 patients with advanced cancer after i.v. (12 mg/m²) and oral (30–35 mg/m²) treatment according to a balanced crossover design. Patients were divided into four groups: subjects who showed normal liver and kidney function (group N), those who presented with normal kidney function and liver metastases (group L), those with kidney dysfunction (creatinine clearance, ≤60 l/h; group R), and those with both liver and kidney dysfunction (group LR). Five patients showed variations in liver or kidney function after the first treatment and were considered to be nonevaluable for the crossover study but evaluable for the liver/kidney function study; some of them appeared in different groups for the i.v. as opposed to p.o. treatments. After i.v. administration, IDA plasma levels followed a triphasic decay pattern. The main metabolite observed in all patients was the 13C-reduced compound (IDAol), which attained plasma levels 2–12 times higher than those of the parent compound. IDA pharmacokinetics was not dependent on the presence of liver metastases but was related to the integrity of kidney function. Analysis of variance indicated a significant correlation between IDA plasma clearance and creatinine clearance; it was also found that IDA plasma clearance was lower in patients whose creatinine clearance was <60 ml/min [group N, 122.8±44.0 l/h; group L, 104.4±27.7 l/h (P=0.58) vs group R, 83.4±18.3 l/h (P=0.037)]. The IDAol terminal half-life and mean residence time (MRT) were significantly increased in patients with impaired kidney function [MRT: group N, 63.6±10.8 h; group L, 69.9±10.2 h (P=0.27) vs group R, 83.2±10.9 h (P=0.025) andt _1/2γ: group N, 41.3±10.1 h; group L, 47.0±7.4 h (P=0.31) vs group R, 55.8±8.2 h (P=0.025)]. After oral treatment, drug absorption occurred during in the first 2–4 h after IDA administration; a biphasic decay pattern was observed thereafter. The main metabolite observed in all patients was again IDAol. The AUC of IDAol was greater after oral administration than after i.v. treatment in proportion to the AUC of IDA (i.v.: AUC-IDAol/AUC-IDA, 2.4–18.9; p.o.: AUC-IDAol/AUC-IDA, 4.1–21.4). Following oral dosing, a substantial amount of 4-demethoxydaunomycinone (AG1) was found in 11/21 patients. No AG1 was detected after i.v. treatment, nor was the corresponding aglycone derived from IDAol found after p.o. or i.v. administration. IDA bioavailability, computed as the ratio of the dose-corrected AUC after p.o. and i.v. treatments in the same patient, was in the 25.2%–35.7% range for groups N, L, and R. Group LR showed a significantly reduced IDA bioavailability (15.7%±5.2%). However, a better description of the actual bioavailability was obtained by taking into account the AUCs of both IDA and IDAol after i.v. and p.o. administration and the relative potency of the two compounds.