Investigation of herb-drug interactions with ginkgo biloba in women receiving hormonal treatment for early breast cancer

Women receiving treatment for breast cancer commonly ingest herbal medicines. Little is known about the potential for herb-drug interactions in this population. The aim of this study is to investigate the effect of ginkgo biloba co-administration on the pharmacokinetics of tamoxifen, anastrozole and letrozole. This was a prospective open-label cross-over study in 60 women with early stage breast cancer taking either tamoxifen, anastrozole or letrozole (n=20/group). Participants received ginkgo biloba (EGb 761) for 3 weeks (120 mg twice daily). Trough concentrations of drugs were measured before and after ginkgo biloba treatment using LC-MS/MS. Toxicities were graded according to National Cancer Institute Common Terminology Criteria for Adverse Events. Trough concentrations before and after treatment with ginkgo biloba were not significantly different for tamoxifen (93.5 ± 29.0, 86.5 ± 25.3 ng/mL; p=0.16), letrozole (91.1 ± 50.4, 89.6 ± 52.14 ng/mL; p=0.60) or anastrozole (29.1 ± 8.6, 29.1 ± 7.6 ng/mL; p=0.97). Ginkgo biloba was well tolerated, with no difference in toxicity during ginkgo biloba. Co-administration of ginkgo biloba does not significantly affect the pharmacokinetics of tamoxifen, anastrozole or letrozole. There was no difference in the toxicity profile of hormone therapy with ginkgo biloba use in women with early stage breast cancer.