Although CYP3A4 inducers may reduce exposure to gefitinib, further work is required to define any resultant effect on the efficacy of gefitinib. Exposure to gefitinib is increased by coadministration with CYP3A4 inhibitors, but since gefitinib is known to have a good tolerability profile, a dosage reduction is not recommended. Gefitinib is unlikely to exert a clinically relevant effect on the pharmacokinetics of drugs that are dependent on CYP2D6-mediated metabolism for their clearance, but the potential to increase plasma concentrations should be considered if gefitinib is coadministered with CYP2D6 substrates that have a narrow therapeutic index or are individually dose titrated.

The gefitinib 250 mg tablet is orally bioavailable in both healthy volunteers and cancer patients; bioavailability is independent of dose and unaffected by food to any clinically significant extent. Gefitinib undergoes rapid plasma clearance and has an extensive volume of distribution, resulting in a pharmacokinetic profile supportive of a once-daily dosage regimen.

These data support the further clinical investigation of ZD 1839. The elimination half-life suggests that once daily oral administration is appropriate.

While tamoxifen use is associated with clear benefits in the treatment of hormone-sensitive breast cancer, it also exhibits partial oestrogen agonist activity that is associated with adverse events, including endometrial cancer. Fulvestrant ('Faslodex') is a new oestrogen receptor antagonist that downregulates the oestrogen receptor and has no known agonist effect. This singlecentre, double-blind, randomised, parallel-group trial was conducted to determine the direct effects of fulvestrant on the female endometrium when given alone and in combination with the oestrogen, ethinyloestradiol. Following a 14-day, pretrial screening period, 30 eligible postmenopausal volunteers were randomised to receive fulvestrant 250 mg, fulvestrant 125 mg or matched placebo administered as a single intramuscular injection. Two weeks postinjection, volunteers received 2-weeks concurrent exposure to ethinyloestradiol 20 mg day 71 . Endometrial thickness was measured before and after the 14-day screening period with further measurements predose (to confirm a return to baseline) and on days 14, 28 and 42 posttreatment with fulvestrant. Pharmacokinetic and safety assessments were performed throughout the trial. Fulvestrant at a dose of 250 mg significantly (P=0.0001) inhibited the oestrogen-stimulated thickening of the endometrium compared with placebo. Neither the 125 mg nor 250 mg doses of fulvestrant demonstrated oestrogenic effects on the endometrium over the initial 14-day assessment period. Fulvestrant was well tolerated and reduced the incidence of ethinyloestradiol-related side effects. At the same dose level that is being evaluated in clinical trials of postmenopausal women with advanced breast cancer, fulvestrant (250 mg) is an antioestrogen with no evidence of agonist activity in the endometrium of healthy postmenopausal women.

No abstract