PURPOSE To define the maximum-tolerated dose (MTD) and better tolerated sequence of paclitaxel by 3-hour infusion plus bolus doxorubicin (DOX) and to evaluate antitumor efficacy. PATIENTS AND METHODS Thirty-five women with metastatic breast cancer (dominant visceral metastases in 56%, and involvement of > or = three sites in 67%) who never received chemotherapy of any type were studied. Paclitaxel every 3 weeks (125 mg/m2 starting dose) was increased by 25-mg/m2 steps in subsequent cohorts of patients. DOX (60 mg/m2 fixed dose) was administered 15 minutes before the start of or after the end of paclitaxel for a maximum of eight cycles. Subsequently, patients in continuous response could receive single-agent paclitaxel (175 to 200 mg/m2 every 3 weeks). The drug sequence was alternated in consecutive patients and in the first two cycles. RESULTS Severe neutropenia that lasted greater than 7 days (n = 4), febrile neutropenia (n = 7) and grade III oral mucositis (n = 6) defined the MTD of paclitaxel at 200 mg/m2 in 34 assessable patients. Grade II peripheral neuropathy occurred in 33% of patients. Six women (18%) developed clinically reversible congestive heart failure (CHF) after a median of 480 mg/m2 total DOX. Drug sequence had no effect on toxicities. High efficacy on all metastatic sites in 32 assessable patients accounted for a 41% complete response (CR) rate (95% confidence interval [CI], 24% to 59%) and 94% overall-response rate (95% CI, 79% to 99%). After a median follow-up of 12 months (range 3 to 18), the median response duration is 8 months (range, 2+ to 18+) for complete responders and 11 months (range 1+ to 15+) for partial responders. CONCLUSION The rate of CR and incidence of CHF may be an expression of therapeutic and toxic enhancement due to the schedule used in this trial. Until clarification of this possibility, this promising combination should be used in investigational trials.

PTX, as clinically formulated in CEL, is responsible for a nonlinear disposition of DOX and DOL. Nonlinearity is PTX- and DOX-dependent, and possibly caused by competition for biliary excretion of taxanes and anthracyclines mediated by P-gp. Nonlinearity indicates that even minor modifications of dose and infusion duration of DOX and PTX may lead to unpredictable pharmacodynamic consequences. The postulated role of P-gp suggests that CEL is clinically active, and advises caution in designing combinations of PTX with other drugs that are substrate for P-gp.

Paclitaxel by a 3-hour infusion in combination with doxorubicin should be investigated in patients with metastatic breast cancer. Unless randomized trials demonstrate greater efficacy of the more toxic higher dose, it is suggested that a dose of 175-200 mg/m2 be administered with the 3-hour infusion schedule.

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ET is feasible, devoid of excessive cardiac toxicity, and active. A reciprocal pharmacokinetic interference between the two drugs has pharmacodynamic consequences, and suggests a direct effect of PTX on EPI metabolism requiring ad hoc investigation.