Pharmacodynamics
NOVALDEX (tamoxifen) is a non-steroidal, triphenylethylene-based drug which displays a complex spectrum of oestrogen antagonist and oestrogen-like pharmacological effects in different tissues. In breast cancer patients, at the tumour level, tamoxifen acts primarily as an antioestrogen, preventing oestrogen binding to the oestrogen receptor. In the clinical situation, it is recognised that tamoxifen leads to reductions in levels of blood total cholesterol and low density lipoproteins in postmenopausal women.
Pharmacokinetics
After oral administration, tamoxifen is absorbed rapidly with maximum serum concentrations attained within 4-7 hours. Steady state concentrations (about 300 ng/mL) are achieved after four weeks treatment with 40 mg daily. The medicine is highly protein bound to serum albumin (> 99 %). Metabolism is by hydroxylation, demethylation and conjugation. Excretion occurs primarily via the faeces. An elimination half-life of approximately seven days has been calculated for the drug itself, whereas that for N-desmethyltamoxifen is 14 days.