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 […]

Herb-Drug Interactions: Cat’s claw

Uncaria tomentosa DC, Uncaria guianensis J.F.Gmel. (Rubiaceae) Synonym(s) and related species Life-giving vine of Peru, Samento, Saventaro, Una de gato. Pharmacopoeias Cat’s Claw (US Ph 32); Powdered Cat’s Claw (US Ph 32); Powdered Cat’s Claw Extract (US Ph 32); Cat’s Claw Tablets (US Ph 32); Cat’s Claw Capsules (The United States Ph 32). Constituents The main constituents of both the closely related species of cat’s claw include the tetracyclic oxindole alkaloids, isorhynchophylline and rhynchophylline, and the indole alkaloids, dihydrocoryynantheine, hirsutine, and hirsuteine. Quinovic acid glycosides have also been isolated. Note that there are two chemotypes of Uncaria tomentosa, one primarily containing the tetracyclic oxindole alkaloids, isorhynochophylline and rhynchopylline, and one primarily containing the pentacychc oxindole alkaloids, (iso)pteropodine and (iso)mitraphylline. Use and indications Cat’s claw roots, bark and leaves have been used for gastric ulcers, arthritis, gonorrhoea, dysentry, herpes zoster, herpes simplex and HIV, and as a contraceptive. In various preclinical studies, antiviral, anti-inflammatory, antirheumatic, immunostimulating, antimutagenic, antitumour and hypotensive 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: Milk thistle

Silybum mahanum (L.) Gaertn. (Asteraceae) Synonym(s) and related species Lady’s thistle, Marian thistle, Mediterranean milk thistle, St Mary’s thistle. Carduus marianus, Mariana lactea Hill. Pharmacopoeias Milk Thistle (US Ph 32); Milk Thistle Capsules (US Ph 32); Milk Thistle Fruit (British Ph 2009, European Ph 2008); Milk Thistle Tablets (US Ph 32); Powdered Milk Thistle (US Ph 32); Powdered Milk Thistle Extract (US Ph 32); Refined and Standardised Milk Thistle Dry Extract (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4). Constituents The mature fruit (seed) of milk thistle contains silymarin, which is a mixture of the flavonolignans silibinin (silybin), silicristin (silychristin), silidianin (silydianin), isosilibinin and others. It may be standardised to contain not less than 1.5% (European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4), or not less than 2% (The United States Ph 32) of silymarin, expressed as silibinin (dried drug). Standardised extracts, containing high levels of silymarin, are often used. Milk thistle fruit also contains various other flavonoids, such as quercetin, and various sterols. Note that milk thistle leaves do not contain silymarin, Read more […]

Herb-Drug Interactions: Ginkgo

Ginkgo biloba L. (Ginkgoaceae) Synonym(s) and related species Fossil tree, Kew tree, Maidenhair tree. Salisburia adiantifolia Sm., Salisburia biloba Hoffmanns. Pharmacopoeias Ginkgo (US Ph 32); Ginkgo capsules (US Ph 32); Ginkgo dry extract, refined and quantified (British Ph 2009, European Ph 2008); Ginkgo leaf (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4); Ginkgo tablets (US Ph 32); Powdered ginkgo extract (The United States Ph 32). Constituents Ginkgo leaves contain numerous flavonoids including the biflavone glycosides such as ginkgetin, isoginkgetin, bilobetin, sciadopitysin, and also some quercetin and kaempferol derivatives. Terpene lactones are the other major component, and these include ginkgolides A, B and C, and bilobalide, Ginkgo extracts may be standardised to contain between 22 and 27% flavonoids (flavone glycosides) and between 5 and 12% terpene lactones, both on the dried basis. The leaves contain only minor amounts of ginkgolic acids, and some pharmacopoeias specify a limit for these. The seeds contain ginkgotoxin (4-O-methylpyridoxine) and ginkgolic acids. Use and indications The leaves of ginkgo are the part usually used. Ginkgo is often used Read more […]

Herb-Drug Interactions: Garlic

Allium sativum L. (Alliaceae) Synonym(s) and related species Ajo, Allium. Pharmacopoeias Garlic (US Ph 32); Garlic Delayed Release Tablets (US Ph 32); Garlic Fluid Extract (US Ph 32); Garlic for Homeopathic Preparations (British Ph 2009, European Ph 2008); Garlic Powder (European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4, British Pharmacopoeia 2009); Powdered Garlic (US Ph 32); Powdered Garlic Extract (The United States Ph 32). Constituents Garlic products are produced from the bulbs (cloves) of garlic and are usually standardised according to the content of the sulphur-containing compounds, alliin, allicin (produced by the action of the enzyme alliinase on alliin) and/or γ-glutamyl-(S)-allyl-L-cysteine. Other sulphur compounds such as allylmethyltrisulfide. allylpropyldisulfide, diallyldisulfide, diallyltrisulfide, ajoene and vinyldithiines, and mercaptan are also present. Garlic also contains various glycosides, monoterpenoids, enzymes, vitamins, minerals and flavonoids based on kaempferol and quercetin. Use and indications Garlic has been used to treat respiratory infections (such as colds, flu, chronic bronchitis, and nasal and throat catarrh) and cardiovascular disorders. It is believed Read more […]