Study of dose escalation and sequence switching of administration of the combination of docetaxel and doxorubicin in advanced breast cancer.

The objectives of the present study were to evaluate whether a schedule-dependent pharmacokinetic and/or pharmacodynamic interaction exists between two sequences of docetaxel and doxorubicin administration and to determine the maximal tolerated dose (MTD) of this combination. Patients with chemotherapy-naïve metastatic or recurrent advanced breast cancer were enrolled. In the crossover design, tandem dose escalation of docetaxel and doxorubicin was performed. Docetaxel, in doses ranging from 50-70 mg/m2, was administered for 1 h by drip infusion either just before or after a 5-min bolus i.v. injection of doxorubicin at dosages from 40-50 mg/ m2. The sequence of drug administration was switched after the first course in each patient, and the sequence of drug administration thereafter depended on the patient's choice. Twenty-five patients were initially assessable for toxicity. The MTD in the sequence of doxorubicin after docetaxel was 40 and 50 mg/m2, respectively, with the dose-limiting toxicity of neutropenia. On the other hand, the MTD of the sequence of docetaxel after doxorubicin was 70 and 50 mg/m2, respectively. The dose-limiting toxicities in this sequence were neutropenia and diarrhea. Duration of grade 4 neutropenia in the sequence of docetaxel followed by doxorubicin was significantly longer than that in the alternate sequence (P = 0.0062). However, there was no difference in pharmacokinetic parameters of docetaxel, doxorubicin, and doxorubicinol between the two sequences. The sequence of 50 mg/m2 doxorubicin followed by 60 mg/m2 docetaxel is recommended for subsequent clinical trials for practical reasons.