Determination of droloxifene and two metabolites in serum by high-pressure liquid chromatography

Pharmacokinetics and metabolism of the anti-oestrogen droloxifene in female human subjects

1. Single oral doses of a solution formulation of (14)C-droloxifene citrate (141 mg) appeared to be rapidly and well absorbed in four post-menopausal female subjects. Peak plasma concentrations (C(max)) of total (14)C (1260 ng eq. ml(-1)), droloxifene (196 ng ml(-1)) and the major metabolite droloxifene glucuronide (851 ng eq. ml(-1)) occurred at 0.9-1.1 h (T(max)) and declined bi-exponentially with terminal half-lives of 45.0, 31.6 and 32.0 h respectively. The mean AUCs of droloxifene and the major metabolite were 21 and 37% respectively that of total (14)C. 2. Total (14)C was excreted slowly, mainly in the faeces. Mean totals of 6.6 and 90.3% of the dose were excreted in the urine and faeces respectively during 11 days. The data were consistent with biliary excretion and enterohepatic circulation of the major metabolite, droloxifene glucuronide. 3. GC-MS showed that the major (14)C-components in 0-24-h urine were droloxifene (mean 0.4% dose) and its glucuronide (2.3% dose), and in faeces were droloxifene (60.2% dose) and N- desmethyldroloxifene (4.2% dose). Other components in faeces corresponded chromatographically to reference standards, droloxifene N-oxide (1.9% dose), side-chain hydroxylated droloxifene (dimethylamine moiety of droloxifene side-chain replaced by hydroxyl, 1.3% dose) and droloxifene glucuronide (10.7% dose). The latter was resistant to enzymic hydrolysis by the beta-glucuronidase used. 4. Intersubject variability in the pharmacokinetics of droloxifene in this study was relatively low (CV < 20% for AUC and half-life).

Selective oestrogen receptor modifiers (SERMs) and breast cancer therapy

Antioestrogen therapy is currently receiving renewed interest for several reasons. Tamoxifen was introduced in the treatment of metastatic breast cancer more than three decades ago. The drug significantly reduces long term mortality and also reduces the risk of contralateral tumours when administered in early breast cancer. Five years of tamoxifen is now standard in adjuvant endocrine therapy, and the drug is currently being evaluated for breast cancer prevention. Despite this, several aspects regarding the pharmacology of the drug are still unclear, and the scientific rationale for dose selection has recently been challenged. Several novel antioestrogen compounds, called selective oestrogen receptor modifiers (SERMs), express selective oestrogen agonistic or antagonistic properties depending on the organ or test system evaluated. Some of these drugs, like raloxifene, do not seem to promote the development of endometrial cancer, although they still have selected oestrogen-like beneficial effects. This paper reviews the pharmacologic and the pharmacokinetic aspects of the different SERMs with particular emphasis on their potential use in therapy and prevention of breast cancer.