Vik SA, Hanley DA, Patten SB, Verhoef M, Brasher P, Hopman W, Anastassiades T, Towheed T.

A preliminary assessment of potential drug-herb interactions in a Canadian population-based study.

University of Calgary, Department of Community Health Sciences, 3330 Hospital Drive NW, Calgary, Alberta T3G 1L4, Canada. savik@ucalgary.ca

PURPOSE: To assess the prevalence of selected potential drug-herb interactions among Canadian Multicentre Osteoporosis participants.

METHODS: Subjects were participants in the Canadian Multicentre Osteoporosis Study (CaMos), a prospective cohort study, evaluating prevalence, incidence and determinants of osteoporosis. Participants were recruited to the study in 1995 from an age-sex stratified random sample of non-institutionalized persons aged >25 years, living within 50 kilometres of one of the nine CaMos study centers. The present analysis is restricted to data collected between 2001-2002, during the 5-year follow-up interviews. Potential drug-herb interactions were selected based on review articles and a recently published book that provided an assessment of the quality of the evidence or clinical impact of drug-herb interactions. The specific criteria included: type of study (e.g. clinical trials versus case reports), report reliability, biological plausibility and the clinical significance of interactions. In this preliminary analysis, the proportion of subjects at-risk for potentially dangerous drug-herb interactions is reported for subjects using the selected cardiovascular (digoxin, furosemide and warfarin) and neuroleptic agents (alprazolam, levodopa, lithium, phenelzine and selective seratonin reuptake inhibitors). The concomitant use of St. John's Wort with cyclosporin, spironolactone or venlafaxine was also examined.

RESULTS: At 5-years, 7652 (81 %) of the original 9423 cohort participants were remaining. The average age was 70 years (range 31-99) and 70% were female. Of the 7652, 1069 (14%) were taking at least one of the prescription medications for which drug-herb interactions were assessed. In total, only 14 (1.3%) of the 1069 participants were using at least one contraindicated drug-herb combination. Of the 514 subjects on one of the cardiovascular medications, 13 (2.5%) were concomitantly using a contraindicated herb. Only one of the 514 subjects taking a neuroleptic agent was identified as at-risk for a potential drug-herb interaction (lithium and psyllium). No subjects were concomitantly using the potentially dangerous combination of St. John's Wort with cyclosporin, spironolactone or venlafaxine.

CONCLUSIONS: Concerns regarding interactions between herbal supplements and prescribed medications have been the subject of much speculation, and previous studies have been limited to convenience samples, primarily on older adults. In this randomly selected, population-based sample we found a relatively low rate of potential drug-herb interactions, most of which were among subjects using specific cardiovascular medications.

 

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