Age-related pharmacokinetics of daunorubicin and daunorubicinol following intravenous bolus daunorubicin administration in the rat.

Age-related differences in pharmacokinetics may be important in determining altered anthracycline cardiotoxicity in the senescent rat and also in older humans. This study examined the effect of aging on daunorubicin pharmacokinetics in the Fischer 344 rat. Daunorubicin 7.5 mg/kg was administered i.v. to 6- and 24-month-old male Fischer 344 rats and plasma and tissue sampling was performed over 168 h for assay of daunorubicin and daunorubicinol concentrations by high-performance liquid chromatography. Systemic clearance of daunorubicin was decreased in older compared to younger animals (56 +/- 4 versus 202 +/- 17 ml min-1 kg-1; P < 0.05). In addition, the area under the plasma daunorubicinol concentration/time curve was significantly increased in older rats. In the heart, the area under the concentration/time curve was significantly increased in senescence both in the case of daunorubicin (201 +/- 12 versus 86 +/- 4 micrograms h g-1; P < 0.05) and daunorubicinol (1347 +/- 118 versus 182 +/- 4 micrograms h g-1; P < 0.05). Furthermore, the peak mean concentrations of daunorubicin were increased in older compared to younger rats both in plasma (1078 +/- 82 versus 663 +/- 66 ng ml-1; P < 0.05) and in heart (27 +/- 1 versus 10 +/- 1 micrograms g-1; P < 0.05). This also was true for daunorubicinol in plasma (284 +/- 39 versus 168 +/- 27 ng ml-1; P < 0.05) and in myocardium (8.6 +/- 0.6 versus 2.4 +/- 0.2 micrograms g-1; P < 0.05). Following daunorubicin injection, the ratio of daunorubicinol to daunorubicin concentrations in tissues increased with time, particularly in plasma and heart in senescent rats. Thus, there are significant age-related changes in daunorubicin and daunorubicinol kinetics in the rat that could alter susceptibility to acute systemic toxicity and to chronic cardiotoxicity.