Asteraceae: Drug Interactions, Contraindications, And Precautions

Patient survey data from Canada, the U.S., and Australia show that one in five patients use prescription drugs concurrently with CAM. The inherent polypharmaceutical nature of complementary and alternative medicine increases the risk of adverse events if these complementary and alternative medicine either have pharmacological activity or interfere with drug metabolism. Since confirmed interactions are sporadic and based largely on case reports, advice to avoid certain drug-CAM combinations is based on known pharmacological and in vitro properties. Known Hypersensitivity to Asteraceae Cross-reactive sesquiterpene lactones are present in many, if not all, Asteraceae. Patients with known CAD from one plant may develop similar type IV reactions following contact with others. Affected patients are often advised to avoid contact with all Asteraceae, yet this advice is based on limited knowledge of cross-reactivity between relatively few members of this large family. Some authorities recommend avoiding Asteraceae-derived complementary and alternative medicine if, for example, the patient is known to have IgE-mediated inhalant allergy to ragweed. While a reasonable approach, this ignores a number of important facts: (1) Read more […]


IMMUNOSUPPRESSANTS are agents that inhibit the body’s reaction to infection or foreign bodies. In this capacity, drugs with this property may be used to prevent tissue rejection following donor grafting or transplant surgery (though there is then the risk of unopposed infection). Also, immunosuppressants are used to treat autoimmune diseases (where the immune system is triggered into acting against systems in the body), including disorders such as rheumatoid arthritis or lupus erythematosus, and also to treat collagen disorders. These agents include cyclosporin, rapamycin and tacrolimus, cytotoxic agents such as azathioprine and cyclophosphamide. and the glucocorticoids. These will be discussed in turn. Cyclosporin is technically an antibiotic, which was discovered serendipitously during a search for antifungal agents and is unique in having a selective action on lymphocytes. It is a cyclic peptide of 11 residues – some previously unknown. It is particularly important as an immunosuppressant in limiting tissue rejection during and following organ transplant surgery. It can also be used to treat severe active rheumatoid arthritis and some skin conditions, such as severe resistant atopic dermatitis and (under supervision) Read more […]

Herb-Drug Interactions: Tea

Camellia sinensis (L.) Kuntze (Theaceae) Synonym(s) and related species Camellia thea Link, Thea sinensis L. Note that Green tea (predominantly produced in China and Japan) is produced from steam-treated tea leaves. Black tea or Red tea (predominantly produced in India, Sri Lanka and Kenya) is processed by fermentation and heating, whereas Oolong tea is partially fermented. Pharmacopoeias Powdered Decaffeinated Green Tea Extract (The United States Ph 32). Constituents Tea contains caffeine (around 1 to 5%), with minor amounts of other xanthines such as theophylline and theobromine. Tea also contains flavonoids, the content of which varies between green (unfermented) and black (fermented) tea. Green tea appears to contain greater quantities of the flavonol-type flavonoids than black tea. Black tea also contains theaflavins, which are produced during the fermentation process. Other flavonols present include quercetin and kaempferol. Oolong tea contains some unique flavones known as oolonghomobisflavins. Tea also contains up to 24% tannins. Use and indications The leaf buds and very young leaves of tea are used as a stimulant and diuretic, actions that can be attributed to the caffeine content. They are Read more […]

Herb-Drug Interactions: St John’s wort

Hypericum perforatum L. (Clusiaceae) Synonym(s) and related species Hypericum, Millepertuis. Hypericum noeanum Boiss., Hypericum veronense Schrank. Pharmacopoeias St John’s Wort (British Ph 2009, European Ph 2008, US Ph 32); St John’s Wort Dry Extract, Quantified (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4). Constituents The main groups of active constituents of St John’s wort are thought to be the anthraquinones, including hypericin, isohypericin, pseudohypericin, protohypericin, protopseudohypericin and cyclopseudohypericin, and the prenylated phloroglucinols, including hyperforin and adhyperforin. Flavonoids, which include kaempferol, quercetin, luteolin, hyperoside, isoquercitrin, quercitrin and rutin; biflavonoids, which include biapigenin and amentoflavone, and catechins are also present. Other polyphenolic constituents include caffeic and chlorogenic acids, and a volatile oil containing methyl-2-octane. Most St John’s wort products are standardised at least for their hypericin content (British Pharmacopoeia 2009), even though hyperforin is known to be a more relevant therapeutic constituent, and some preparations are now standardised for both (The United Read more […]

Herb-Drug Interactions: Schisandra

Schisandra chinensis K.Koch (Schisandraceae) Synonym(s) and related species Gomishi (Japanese), Magnolia vine, Wu-Wei-Zi (Chinese). Kadsura chinensis Turcz. Schisandra sphenanthera Rehder & EH Wilson is often used with, or substituted for, Schisandra chinensis. Other species of Schisandra are also used medicinally in China. Constituents The major active components of the fruits of Schisandra chinensis are dibenzocyclooctene lignans. The identity and nomenclature are confusing, because, when originally isolated by different researchers, the same compounds were given different names. The main groups of compounds are the schisandrins (schizandrins) and the gomisins (some of which were originally called wuweizu esters) and their derivatives. Schisandrin is also referred to in the literature as schisandrol A, gomisin A as schisandrol B, deoxyschisandrin as schisandrin A or wuweizu A, and schisantherin B as gomisin B or wuweizu B, for example. An essential oil contains borneol, 1,8-cineole, citral, sesquicarene and other monoterpenes. Extracts of Schisandra sphenanthera are reported to have a fairly similar chemical composition. Use and indications Schisandra is a very important herb in Chinese medicine. Read more […]

Herb-Drug Interactions: Grapefruit

Citrus paradisi Macfad. (Rutaceae) Synonym(s) and related species Citrus paradisi Macfad. Grapefruit is a hybrid of the Pummelo or Pomelo (Citrus maxima (Burm.) Merr) with the sweet orange (Citrus sinensis (L.) Osbeck). Constituents Grapefruit contains furanocoumarins including bergamottin, 6′,7′-dihydroxybergamottin, bergapten, bergaptol, geranyl-coumarin and paradisin A, flavonoid glycosides such as naringin and flavonoid aglycones galangin, kaempferol, morin, naringenin, quercetin and others. The peel contains a volatile oil, mostly composed of limonene. Note that some grapefruit seed extracts have been found to contain preservatives such as benzethonium chloride, triclosan and methyl-p-hydroxybenzoate, which might be present because of the methods of production. Use and indications Grapefruit is used as a source of flavonoids (citrus bioflavonoids), which are widely used for their supposed antioxidant effects, and are covered under flavonoids. Grapefruit seed extracts are used for their antimicrobial properties, but there is some controversy that this might be due to preservative content rather than natural constituents. Grapefruit and grapefruit juice are commonly ingested as part of the diet, Read more […]

St John’s wort: Significant Interactions

St John’s wort is one of the few herbal medicines that has been subjected to controlled studies in order to determine the significance of its interaction with numerous drugs. Although this can be reassuring, the clinical significance of many interactions is still unpredictable because of the variable chemical composition of products. It is important to note that interactions due to CYPand P-gp induction do not appear significant with low hyperforin extracts (ZE 117). Clinical note— Mechanisms responsible for reported interactions Based on the herb’s pharmacology, there are several mechanisms by which it may interact with drugs. Considering St John’s wort has significant serotonin reuptake inhibitor activity and significantly upregulates both 5-HT1A and 5-HT2A receptors, concomitant use of drugs that elevate serotonin levels, such as tricyclic antidepressants or SSRIs, may result in additive or synergistic effects and increase the risk of serotonergic syndrome. As the constituent hyperforin has a significant and selective induction effect on CYP3A4 and 2C19 activity and induces the drug transporter P-glycoprotein, a number of pharmacokinetic interactions are possible with those drugs that are substrates for Read more […]