Letrozole (trademark Femara) is a new orally active, potent and selective aromatase inhibitor for the hormonal treatment of advanced breast cancer in postmenopausal women. The pharmacokinetics of letrozole and the suppression of peripheral estrogens were studied in 28 breast cancer patients after a single dose and at steady state. The pharmacokinetics of two distinct age groups (> or =50, < or =65, N=15 and > or =70 years old, N=9) were compared. There were no significant differences in area under the curve (AUC) or terminal half-life between the two age groups neither after a single dose nor at steady state. However, when comparing steady state to single dose kinetics, half-life and AUC increased significantly by 42% (90% CI: 1.13, 1.78) and 28% (90% CI: 1.12, 1.47), respectively. This deviation from linearity was probably due to a partial saturation or auto-inhibition of the dominant metabolic clearance mechanism of letrozole. At steady state, approximately 70% of the administered dose was excreted in urine as unchanged letrozole (6.0+/-3.8%) or as the glucuronide of the major, pharmacologically inactive metabolite CGP44645 (64.2+/-22.7%). A single dose of letrozole caused suppression of serum estrogen levels close to the quantification limit of the assay. No difference between single dose suppression and suppression at steady state could be detected.

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From February 1987 to January 1989, 60 patients with advanced breast cancer and no prior chemotherapy for advanced disease were randomized and studied, with 31 treated with fluorouracil, epirubicin, and cyclophosphamide (FEC) and 29 patients with fluorouracil, mitoxantrone, and cyclophosphamide (FNC). Doses were 500 mg/m2 fluorouracil, 500 mg/m2 cyclophosphamide, and 50 mg/m2 epirubicin2 or 10 mg/m mitoxantrone, i.v. Day 1 every 3 weeks. There were no statistically significant differences in pretreatment patient characteristics between the groups. Fifty-six patients were evaluable for response (29 in the FEC arm and 27 in the FNC arm). The response rates were 48.2% for the FEC group (complete response (CR) 10.3% and partial response (PR) 37.9%) and 40.7% for the FNC group (CR 3.7% and PR 37%) (not significantly different, NS). The median response duration was 247 and 267 days, respectively (NS), the median time to progression and time to treatment failure was 244 and 155.5 days for the FEC group and 86 and 98 days for the FNC group, respectively (NS). The incidence of nausea/vomiting was 87.1% in the FEC group and 79.3% in the FNC group, with comparable severity. Alopecia occurred in 80.6% of FEC patients and 44.8% of FNC patients (p less than 0.05). The incidences and degrees of severity of leukopenia, anemia, and cardiotoxicity were comparable in the two treatment groups. Efficacy and toxicity of the two regimens were quite similar. FNC can improve the quality of life of patients by providing significantly less alopecia.

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