Abstract
Background: Tamoxifen is an important drug in chemotherapy being part of various protocols in cancer treatment, but is not universally effective even when used before surgery or in preventing recurrence. Pharmacogenetic variability in drug metabolism is one possible mechanism of treatment failure. We hypothesize that Drug-Herb Interactions (DHI) contribute in disease outcomes, nevertheless the functional single nucleotide polymorphisms in drug metabolizing enzymes that activate cytochrome enzymes. Methods: We performed a retrospective study in the last 9 years of clinical cases enrolled in follow up of Observatory of Drug-Herb Interactions, University of Coimbra - Portugal (www.oipm.uc.pt), and the data collected will be discussed in this paper. Data obtained from PubMed and from PubChem Compounds with preference given to the data obtained during the last 10 years, was also obtained. The search terms were varied depending of the Clinical situation. Results: From our experience, in order to avoid the major predictable DHI more observational trials should be carried out for therapeutic protocols associated to tamoxifen. The most consumed, fruits and vegetables, medicinal plants and other natural products associated to the intake of tamoxifen were, for example, Orange and Better juice, Aloe, Geranium, Saint John Wort leaves and flowers, roots as Astragalus, Curcuma, Ginger, Ginseng, Rehmanniae and Valeriana, mushrooms as Coriolus, Maitake, Shiitake and Reishi. Conclusions: Based on the major compounds involved in those products will be predictable how to advice patients doing this kind of treatment and follow a possible therapy failure, or even a toxic event. Our group did a flyer with the main possible interactions selected for DHI with Tamoxifen. This it will be given to patients doing therapy with tamoxifen, helping them to be a aware of the situation and involving all in the resolution for a better outcome (it will be available in our website as other materials for download already posted there).
Highlights
Tamoxifen can be used in several ways, as for instance, to lower the chances of cancer coming back and is usually taken for 5 to 10 years but can be prescribed before surgery too [1]
Our group did a flyer with the main possible interactions selected for Drug-Herb Interactions (DHI) with Tamoxifen
These data was corroborate by Knox et al, showing that “the 2-year relapse-free survival was 68% in patients who are poor metabolizers of CYP2D6 and patients on strong inhibitors of CYP2D6 compared to 98% in patients who are extensive metabolizers of CYP2D6” [4]
Summary
Tamoxifen can be used in several ways, as for instance, to lower the chances of cancer coming back and is usually taken for 5 to 10 years but can be prescribed before surgery too (neoadjuvant therapy) [1]. In both situations, the effectiveness of the drug is crucial for the outcome. The genetic idiosyncrasy, since that 7% of the Caucasian population are slowly (poor metabolizers) of CYP2D6 [2]. Tamoxifen is one among other drugs that suffer often DHI with one of the two possible outcomes, increased side effects or therapeutic failure
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