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Faslodex

Clinical Pharmacology
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Clinical Pharmacology

Faslodex

Pediatric:
The pharmacokinetics of fulvestrant have not been evaluated in pediatric patients.

Drug-Drug Interactions:

There are no known drug-drug interactions. Fulvestrant does not significantly inhibit any of the major CYP isoenzymes, including CYP 1A2, 2C9, 2C19, 2D6, and 3A4 in vitro, and studies of co-administration of fulvestrant with midazolam indicate that therapeutic doses of fulvestrant have no inhibitory effects on CYP 3A4 or alter blood levels of drug metabolized by that enzyme. Although fulvestrant is partly metabolized by CYP 3A4, a clinical study with rifampin, an inducer of CYP 3A4, showed no effect on the pharmacokinetics of fulvestrant. Also results from a healthy volunteerstudy with ketoconazole, a potent inhibitor of CYP3A4, indicated that ketoconazole had no effect on the pharmacokinetics of fulvestrant and dosage adjustment is not necessary in patients co-prescribed CYP 3A4 inhibitors or inducers.

CLINICAL STUDIES

Efficacy of FASLODEX was established by comparison to the selective aromatase inhibitor anastrozole in two randomized, controlled clinical trials (one conducted in North America, the other predominately in Europe) in postmenopausal women with locally advanced or metastatic breast cancer. All patients had progressed after previous therapy with an antiestrogen or progestin for breast cancer in the adjuvant or advanced disease setting. The majority of patients in these trials had ER+ and/or PgR+ tumors. Patients who had ER-/PgR- or unknown disease must have shown prior response to endocrine therapy.

In both trials, eligible patients with measurable and/or evaluable disease were randomized to receive either FASLODEX 250 mg intramuscularly once a month (28 days ± 3 days) or anastrozole 1 mg orally once a day. All patients were assessed monthly for the first three months and every three months thereafter. The North American trial was a double-blind, randomized trial in 400 postmenopausal women. The European trial was an open, randomized trial conducted in 451 patients. Patients on the FASLODEX arm of the North American trial received two separate injections (2 X 2.5 mL), whereas FASLODEX patients received a single injection (1 X 5 mL) in the European trial. In both trials, patients were initially randomized to a 125 mg per month dose as well, but interim analysis showed a very low response rate and low dose groups were dropped.

The effectiveness endpoints were response rates (RR), based on the Union Internationale Contre le Cancer (UICC) criteria, and time to progression (TTP). Survival time was also determined. Confidence intervals (95.4%) were calculated for the difference in RR between the FASLODEX and anastrozole groups. The hazard ratio for an unfavorable event, (such as disease progression or death) between FASLODEX and anastrozole groups was also determined.

Table 2 provides the demographics and baseline characteristics of the postmenopausal women randomized to FASLODEX 250 mg or anastrozole 1 mg.

TABLE 2: STUDY POPULATION DEMOGRAPHICS

 
NorthAmerican Trial
EuropeanTrial
Parameter
FASLODEX
250 mg
Anastrozole
1 mg
FASLODEX
250 mg
Anastrozole
1 mg
No. of Participants
206
194
222
229
Median Age (yrs)
64
61
64
65
Age Range (yrs)
33 - 89
36 - 94
35 - 86
33 - 89
Receptor Status # (%)
ER Positive
170 (83%)
156 (80%)
156 (70%)
173 (76%)
ER/PgR Positive
179 (87%)
169 (87%)
163 (73%)
183 (80%)
ER/PgR Unknown
13 (6%)
15 (8%)
51 (23%)
37 (16%)
Previous Therapy
Tamoxifen
196 (95%)
187 (96%)
215 (97%)
225 (98%)
Adjuvant antiestrogen only
94 (46%)
94 (48%)
95 (43%)
100 (44%)
Brand Name: Faslodex
Generic Name: Fulvestrant
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