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Stockley's Herbal Medicines Interactions

Stockley’s Herbal Medicines Interactions by Elizabeth Williamson, Samuel Driver, and Karen Baxter (eds). Chicago, IL: Pharmaceutical Press; 2009. Hardcover; 423 pages. ISBN 978-0-85369-760-2. $89.95. Available in ABC’s online store.

The editors and their staff (comprised of British pharmacists who are experts in the study of drug interactions) produced this first edition to address herbal interactions with conventional drugs from a clinical perspective. Co-editor Elizabeth Williamson was relied on for her herbal medicine expertise, as chair of the Expert Advisory Group for Herbal and Complementary Medicines for the British Pharmacopoeia Commission. The other contributors appear well-qualified to assess the interactions data from a pharmaceutical perspective.

My first impression involved the inappropriateness of the cover title. The title page provides a subtitle for clarification: “A guide to the interactions of herbal medicines, dietary supplements and nutraceuticals with conventional medicines.” Though the book is enhanced by its broad perspective, the inclusion of nonbotanical health agents such as acidophilus, chitosan, chondroitin, coenzyme Q10, creatine, glucosamine, and melatonin under the title “herbal medicines” is unfortunate. We are far past the time when agents derived from animals should be considered under this heading. Other items covered include berberine, caffeine, beta-carotene, lycopene, and resveratrol, which could be described better as plant-derived isolates, in contrast to complex herbal medicines. Due to widespread media perpetuation of such confusion, it is especially important in a science-based text that such distinctions are patently acknowledged.

Coming from their work on the well-respected and clinically-based Stockley’s Drug Interactions, the editors and staff acknowledge that most of the experimental evidence for herbal-drug interactions does not meet the standards necessary to establish their clinical relevance. Nonetheless, a growing body of data indicates that pertinent evidence should be scrutinized to help health practitioners avoid foreseeable risks and be appropriately alerted to concerns. Based on their relative popularity, some herbs are included even when data are unavailable on pharmacokinetic or pharmacodynamic interactions, e.g., avens (Geum urbanum, Rosaceae) and pumpkin (Cucurbita pepo, Cucurbitaceae).

Consequently, the inclusion of over 150 common herbs and nutraceuticals does not reflect the number with documented interactions. Some chemical categories of agents that can be found in a wide variety of plants are discussed as separate items, i.e., flavonoids, isoflavones, and natural coumarins. The index serves as a useful resource to identify specific compounds from these groups along with herbs and a listing of the associated drugs with which they individually interact, and vice versa.

The herbs are arranged alphabetically in the text according to their common names, with the scientific and pharmacopeial nomenclature also provided. Short summaries on constituents, uses/indications, the impact on drug pharmacokinetics, and an interaction overview are given for each. Since no separate heading is designated for the therapeutic part of the plant, sometimes this important information fails to be recorded. When interactions are identified for a natural medicinal agent, they are presented as separate sections (“monographs”) on single drugs or groups of drugs, occasionally along with other monographs for foods, herbal medicines, and supplements. Clinical evidence is given when the interactions are documented in humans. Experimental evidence from animal and in vitro studies is used to describe the mechanism of interaction as well as theoretical interactions. The authors explain that the sparsity of clinical interaction research for botanicals requires including this speculative approach. All interaction data are referenced.

The relative importance of the listed interactions is addressed, based on the weight of evidence and severity of outcome, suggesting appropriate actions such as substituting safer alternative agents. The potential seriousness of the listed interactions is designated according to a simple rating system using 5 symbols to indicate a clinical course: (1) avoiding due to potential life-threatening outcome, (2) adjusting dosage and monitoring closely for significant hazards, (3) advising about potential hazards when evidence is poor, (4) giving guidance on possible adverse effects and monitoring when the outcome is doubtful, and (5) reassuring the patient when there is no clinically-significant risk.

Many, if not most, of the designations given for the listed interactions in the text are indicative of uncertainty (numbers 3 and 4). The judgements are based on objective data but also involve subjective assessment, so obviously not every ranking will meet with universal agreement. In light of the challenging subject matter, some assessments could have been enhanced by greater collaboration with herbal medicine authorities. Since all degrees of actual or potential interactions are listed together under each herb, these symbols do provide a simple visual means of identifying their relevance.

This books provides a comparatively comprehensive and reliable source of information regarding pre-clinical and clinical research on mostly herbal medicinal agents. Under the heading of “General Considerations” at the beginning, the authors acknowledge the complexities and limitations of organizing and delivering information on this subject. Difficulties in drawing conclusions arise from variations in herbal preparations and dosage, types and qualities of evidence, and differences between individuals in regard to age, genetic and metabolic profiles, pathophysiology, etc. They have done a respectable job of keeping the information in a clinical context by establishing criteria for judging clinical relevance and identifying it with an easily grasped system of symbols.

I would recommend this book especially for those practitioners who are not experts in botanical prescribing and therefore need to rely heavily on others’ knowledge and judgements. The authors themselves recognize that the variety of preparations for any given botanical changes the degree of potential risk associated with a particular preparation, depending on its specific phytochemical content and concentration. The accuracy and value of this and similar books will undoubtedly increase in succeeding editions as better research data and knowledge continue to accrue. The necessary generalizations provided in this text are best utilized when adapted by practitioners according to the particular herbal preparation used and the individual patient under their care. Given its inherent limitations, this book can serve as an important resource to help sort through the varying shades of likelihood and uncertainty.

–Francis Brinker, ND Clinical Assistant Professor Department of MedicineUniversity of Arizona Tucson, AZ