title: Inhibition of human cytochrome p450 metabolism by blended herbal products and vitamins.
abstract: OBJECTIVE
  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 tBC 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.
authors.affiliation: Centre for Research in Biopharmaceuticals and Biotechnology, University of Ottawa, Ottawa, ON, Canada.
authors.forename: Teresa W
authors.initials: TW
authors.lastname: Tam
authors.forename: Humayoun
authors.initials: H
authors.lastname: Akhtar
authors.forename: John Thor
authors.initials: JT
authors.lastname: Arnason
authors.forename: Kosta
authors.initials: K
authors.lastname: Cvijovic
authors.forename: Heather
authors.initials: H
authors.lastname: Boon
authors.forename: D William
authors.initials: DW
authors.lastname: Cameron
authors.forename: Cathy E
authors.initials: CE
authors.lastname: Drouin
authors.forename: Walter
authors.initials: W
authors.lastname: Jaeger
authors.forename: Ross T
authors.initials: RT
authors.lastname: Tsuyuki
authors.forename: Sunita
authors.initials: S
authors.lastname: Vohra
authors.forename: Brian C
authors.initials: BC
authors.lastname: Foster
mesh_terms: D000328:Adult; D002762:Cholecalciferol / Q000009:adverse effects / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D019587:Dietary Supplements; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000009:adverse effects* / Q000494:pharmacology; D005260:Female; D006801:Humans; D010936:Plant Extracts / Q000009:adverse effects* / Q000494:pharmacology; D014815:Vitamins / Q000009:adverse effects* / Q000494:pharmacology; D019207:beta Carotene / Q000009:adverse effects / Q000494:pharmacology
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010936:Plant Extracts; D014815:Vitamins; D019207:beta Carotene; D002762:Cholecalciferol; D003577:Cytochrome P-450 Enzyme System