Epirubicin plasma and blood pharmacokinetics after single i.v. bolus in advanced cancer patients.

Plasma and whole blood pharmacokinetics of epirubicin (4'-epidoxorubicin, epiDX), a new doxorubicin (DX) analogue with an improved spectrum of activity and lower toxicity, were investigated in advanced cancer patients after i.v. bolus administration. Drug decay is triphasic, with a long terminal half-life. Plasma and blood levels of the C-13 reduced epiDX metabolite, epirubicinol (epiDXol), are lower than those of the parent compound. Glucuronides of epiDX and epiDXol are also present in plasma, bile and urine; similar compounds are not described in the literature among the metabolites of DX. EpiDX plasma clearance is consistently higher and mean residence time lower than the corresponding DX parameters, thus indicating a more efficient disposition of the new drug. This behaviour is also reflected in a faster elimination of epiDXol with respect to the corresponding Dx metabolite, doxorubicinol. After an initial induction period, epiDX concentration is higher in whole blood than in plasma. Blood clearance is lower than plasma clearance; volume of distribution at steady state Vss is lower if blood concentration data are used in the pharmacokinetic analysis. Mean Residence Time is similar in plasma and blood. A statistically significant reduction of clearance parameters is observed in patients with liver metastases, even in the absence of altered bilirubin levels. Drug clearance problems induced by renal dysfunction become relevant only in severe renal failure.