Tamoxifen inhibits cytochrome P450 2C9 activity in breast cancer patients.

Article Details

Citation

Boruban MC, Yasar U, Babaoglu MO, Sencan O, Bozkurt A

Tamoxifen inhibits cytochrome P450 2C9 activity in breast cancer patients.

J Chemother. 2006 Aug;18(4):421-4. doi: 10.1179/joc.2006.18.4.421.

PubMed ID
17024799 [ View in PubMed
]
Abstract

Tamoxifen has been reported to potentiate the anticoagulant effect of warfarin and also to increase the plasma level of phenytoin, which are mainly metabolized by CYP2C9. The aim of this study was to determine the influence of tamoxifen on CYP2C9 activity in vivo in humans. Thirteen breast cancer patients who would start tamoxifen following cytotoxic chemotherapy were enrolled in the study. A single oral dose of 25 mg losartan was given to the patients 2 days before and 2 weeks after starting tamoxifen therapy. Losartan and E3174 in 8-hour urine samples were measured by HPLC. Tamoxifen significantly increased the average urinary losartan/E3174 ratio from 0.73 (CI 95% = 0.15 - 2.30) to 1.66 (CI 95% = 0.68 - 5.20), after 2 weeks of treatment (p = 0.002). Tamoxifen inhibited CYP2C9 activity in breast cancer patients within two weeks of its administration. The inhibition of CYP2C9 activity may be a possible explanation for the drug-drug interaction of tamoxifen with CYP2C9 substrates.

DrugBank Data that Cites this Article

Drug Enzymes
DrugEnzymeKindOrganismPharmacological ActionActions
TamoxifenCytochrome P450 2C9ProteinHumans
Unknown
Substrate
Inhibitor
Details