Docetaxel in combination with epirubicin in metastatic breast cancer: pharmacokinetic interactions

Epirubicin (75 mg/m2) and docetaxel (75 mg/m2) were administered to 16 patients affected by metastatic breast cancer following two different schedules: (1) docetaxel as infusion administered 1 h after epirubicin administration (schedule A); and (2) docetaxel as infusion immediately (10 min) after the end of epirubicin i.v. bolus administration (schedule B). Experimental non-compartmental analyses such as AUC and Css, were affected very little by the drug combination, irrespective of whether the administration of docetaxel was immediately after the epirubicin bolus (10 min) or delayed (1 h). However, serum levels showed evidence of transient drug interaction: in schedule A, docetaxel infusion was associated with a transient increase of plasma epirubicin in correspondence with Cssmax of docetaxel. Bi-compartmental analysis showed a significant difference in epirubicin clearance between protocols A and B. It is suggested that polysorbate 80, used in minimal amounts to formulate docetaxel, may interfere with epirubicin plasma level.