Inhibition of Human Cytochrome P450 Metabolism by Blended Herbal Products and Vitamins

Teresa W Tam1, Humayoun Akhtar2, John Thor Arnason1, Kosta Cvijovic3, Heather Boon3, D William Cameron4, Cathy E Drouin1, Walter Jaeger5, Ross T Tsuyuki6, Sunita Vohra7, Brian C Foster8

1Centre for Research in Biopharmaceuticals and Biotechnology, University of Ottawa, Ottawa, ON
2Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, ON
3Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, ON
4Faculty of Medicine, Univeristy of Ottawa, Ottawa, ON
5Department of Clinical Pharmacy and Diagnostics, University of Vienna, Vienna
6Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB
7CARE Program, Faculty of Medicine and School of Public Health, University of Alberta, Edmonton, AB
8Office of Science, Therapeutic Products Directorate, Health Canada, Ottawa, ON


Purpose. The use of supplements as herbal and micronutrient natural health products with conventional health products has become increasingly popular. It has been reported that some herbal products can inhibit the activity of cytochrome P450-mediated metabolism and drug disposition. This study was designed to investigate a case report of a severe adverse event to determine the potential interactions of femMED, Thyrosense and vitamins on cytochrome P450-mediated drug metabolism.
Methods. The effect of extracts from these commercially available herbal formulations, trans-ß-carotene, multivitamins, and vitamin D3 supplements on cytochrome P450-mediated drug metabolism of marker substrates was determined in vitro.
Results. The blended herbal products femMED and Thyrosense had a high potential to affect the safety and efficacy of many health products. Some vitamin and trans-β-carotene containing products also have the potential to affect drug disposition. The ß-carotene content of various products was analyzed and significant discrepancies were found among them and between values indicated on product labels. Product extracts also exhibited a low to moderate capacity to inhibit cytochrome P450 2C9, 2C19 and 3A4-mediated metabolism.
Conclusions. The findings of this study suggest that these herbal products and most vitamin products may have an inhibitory effect on cytochrome P450 activity that could contribute to development of an adverse event. Further work is warranted to determine how supplementation with these products may affect drug metabolism in an in vivo context.

J Pharm Pharm Sci, 14 (1): 1-16, 2011

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