Top Gene Interactions
- Metabolism: Hepatic. Tamoxifen is extensively metabolized after oral administration. N-Desmethyl-tamoxifen is the major metabolite found in plasma. N-Desmethyl-tamoxifen's activity is similar to tamoxifen. 4-hydroxy-tamoxifen and a side chain primary alcohol derivative of tamoxifen have been identified as minor metabolites in plasma. 4-Hydroxy-tamoxifen formation is catalyzed mainly by cytochrome P450 (CYP) 2D6, and also by CYP2C9 and 3A4. At high tamoxifen concentrations, CYP2B6 also catalyzes 4-hydroxylation of the parent drug. 4-Hydroxy-tamoxifen possesses 30- to 100-times greater affinity for the estrogen receptor and 30- to 100-times greater potency at inhibiting estrogen-dependent cell proliferation compared to tamoxifen. It is also metabolized by flavin monooxygenases FMO1 and FMO3 to form tamoxifen-N-oxide. Route of Elimination: 65% of the dose was excreted from the body over 2 weeks in which fecal excretion was the primary route of elimination. Tamoxifen is excreted mainly as polar conjugates, with unchanged drug and unconjugated metabolites accounting for less than 30% of the total fecal radioactivity. Half Life: The decline in tamoxifen plasma concentrations is biphasic with a terminal elimination half-life of approximately 5 to 7 days. The estimated half-life of N-desmethyl tamoxifen is 14 days.
- Uses/Sources: Tamoxifen is indicated for the treatment of metastatic breast cancer in women and men and ductal carcinoma in Situ.
- Symptoms: Signs observed at the highest doses following studies to determine LD50 in animals were respiratory difficulties and convulsions.
- Route of Exposure: When a single oral dose of 20 mg is given, the average peak plasma concentration (Cmax) is 40 ng/mL which occurred approximately 5 hours after dosing (Tmax). The Cmax of N-desmethyl tamoxifen is 15 ng/mL. Steady-state concentrations for tamoxifen is achieved in 4 weeks, while steady-state concentrations for N-desmethyl tamoxifen is achieved in 8 weeks.
Mechanism of Action
|Target Name||Mechanism of Action||References|
Estrogen receptor beta
Cytochrome P450 19A1
Nuclear receptor subfamily 1 group I member 2
Sodium-dependent dopamine transporter
Sodium-dependent noradrenaline transporter
D(1A) dopamine receptor
5-hydroxytryptamine receptor 6
Nuclear factor erythroid 2-related factor 2
Protein kinase C