Stevia: Stevioside

Absorption, distribution and metabolism In the rat, stevioside (125 mg/kg; p.o.) has a half-life of 24 hour, and is largely excreted in the feces in the form of steviol. Other metabolites include steviolbioside. In this species, at least, metabolism appears to be mediated primarily by the gut microflora. Thus, [17-14C] stevioside is converted to steviol by suspensions of rat intestinal microflora. Conversion is complete within two days. The distribution of a derivative, [131I]iodostevioside (position of the label not reported), has been studied in rats following i.v. administration. Radioactivity rapidly accumulated first in the small intestine and then in the liver. Within two hours, 52% of the radioactivity administered appeared in the bile. The largest biliary component was [131I]iodosteviol (47% of total radioactivity), followed by [131I]iodostevioside (37%) and an unidentified metabolite (15%). Non-enzymatic conversion of stevioside to steviol does not occur. Acid hydrolysis yields isosteviol, while incubation for up to three months under conditions ranging pH 2–8 and 5 to 90 °C does not result in detectable formation of steviol. Stevioside appears to be poorly transported across the cell membrane. No Read more […]

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 […]

CALCIUM-CHANNEL BLOCKERS

CALCIUM-CHANNEL BLOCKERS are agents that literally block or close any of the many types of calcium channels. However, in common usage the term is mainly used to describe a class of drugs finding increasing application in therapeutics (also called calcium antagonists or calcium-entry blockers) typified by the dihydropyridines (DHPs). In a more general usage of the term, there are many different classes of calcium-channel blockers, and many types of calcium channels. See CALCIUM-CHANNEL ACTIVATORS. First, in the cell membrane, the voltage-gated calcium channels are of at least six types — termed L, N, T, P, Q, R — that may be differentiated by electrophysiological, molecular cloning and pharmacological criteria. The L- and N-channels are high-voltage activated, voltage-dependent and undoubtedly of great importance in normal physiology; L mainly in smooth, cardiac and skeletal muscle (and some neurons), but N only in neurons. T-channels are important in repetitive activity in cardiac SA node of the heart, neurons and some endocrine cells. The remainder have been found more recently in neurons. These channels are products of different genes, but they all share great structural similarity — both with respect to Read more […]

Herb-Drug Interactions: Valerian

Valeriana officinalis L. (Valerianaceae) Synonym(s) and related species All-heal, Belgian valerian, Common valerian, Fragrant valerian, Garden valerian. Many other Valerian species are used in different parts of the world. Pharmacopoeias Powdered Valerian (The United States Ph 32); Powdered Valerian Extract (The United States Ph 32); Valerian (British Ph 2009, The United States Ph 32); Valerian Dry Aqueous Extract (European Ph 2008); Valerian Dry Hydroalcoholic Extract (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4); Valerian Root (European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4); Valerian Tablets (The United States Ph 32); Valerian Tincture (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4). Constituents Valerian root and rhizome contains a large number of constituents which vary considerably according to the source of the plant material and the method of processing and storage. Many are known to contribute to the activity, and even those that are known to be unstable may produce active decomposition products. The valepotriates include the valtrates, which are active constituents, but decompose on storage to form other Read more […]

Herb-Drug Interactions: Turmeric

Curcuma longa L. (Zingiberaceae) Synonym(s) and related species Indian saffron. Curcuma domestica Valeton is generally accepted to be the same species as Curcuma longa. The related species Curcuma aromatica Salisb. is known as wild or aromatic turmeric and Curcuma xanthorrhiza D. Dietr. is known as Javanese turmeric. Not to be confused with Curcuma zedoaria (Christmann) Roscoe, which is zedoary. Pharmacopoeias Javanese Turmeric (British Ph 2009, European Ph 2008); Turmeric (US Ph 32); Powdered Turmeric (US Ph 32); Powdered Turmeric Extract (The United States Ph 32). Constituents The active constituents are curcuminoids, and include a mixture known as curcumin which contains diferuloylmethane (sometimes referred to as curcumin or curcumin I), desmethoxycurcumin (curcumin II), bisdesmethoxycurcumin (curcumin III) and cyclocurcumin (curcumin IV). Most commercially available preparations of ‘curcumin’ are not pure, but also contain desmethoxycurcumin and bisdesmethoxycurcumin. The related species Curcuma aromatica and Curcuma xanthorrhiza also contain curcuminoids. The essential oil contains mainly turmerones, including zingiberene. Use and indications Turmeric has many biological activities, which 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: Senna

Cassia senna L, Cassia angustifolia Vahl. (Fabaceae) Synonym(s) and related species Indian senna. Cassia acutifolia Delile, Senna alexandrina Mill. Senna obtained from Cassia senna is also known as Alexandrian senna or Khartoum senna, and senna obtained from Cassia angustifolia is also known as Tinnevelly senna. Pharmacopoeias Alexandrian Senna Fruit (British Ph 2009); Senna Fluid Extract (US Ph 32); Senna Leaf (British Ph 2009, European Ph 2008, US Ph 32); Senna Liquid Extract (British Ph 2009); Senna Oral Solution (US Ph 32); Senna Pods (US Ph 32); Senna Pods, Alexandrian (European Ph 2008); Senna Pods, Tinnevelly (European Ph 2008); Senna Tablets (British Ph 2009); Sennosides (US Ph 32); Standardised Senna Granules (British Ph 2009); Standardised Senna Leaf Dry Extract (British Ph 2009, European Ph 2008); Tinnevelly Senna Fruit (British Pharmacopoeia 2009). Constituents Anthraquinone glycosides are major components of senna. In the leaf the anthraquinones include sennosides A, B, C and D, and palmidin A, rhein anthrone and aloe-emodin glycosides. The fruit contains sennosides A and B and a closely related glycoside, sennoside Al. Senna is usually standardised to the content of sennosides, generally Read more […]

Herb-Drug Interactions: Pepper

Piper nigrum L. (Piperaceae) Synonym(s) and related species Black and white pepper are derived from the fruits of the same species, Piper nigrum L. Black pepper is the unripe fruit which has been immersed in hot water and dried in the sun, during which the outer pericarp shrinks and darkens into a thin, wrinkled black layer. White pepper consists of the seed only, prepared by soaking the fully ripe berries, removing the pericarp and drying the naked seed. Long pepper, Piper longum L., is a closely related species where the fruits are smaller and occur embedded in flower ‘spikes’, which form the seed heads. Constituents Alkaloids and alkylamides, the most important being piperine, with piperanine, piperettine, piperlongumine, pipernonaline, lignans and minor constituents such as the piperoleins, have been isolated from the fruits of both species of pepper. Black pepper and long pepper also contain a volatile oil which may differ in constitution, but is composed of bisabolene, sabinene and many others; white pepper contains very little. The pungent taste of pepper is principally due to piperine, which acts at the vanilloid receptor. Use and indications Pepper is one of the most popular spices in the world, 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 […]

Herb-Drug Interactions: Flavonoids

Bioflavonoids The flavonoids are a large complex group of related compounds, which are widely available in the form of dietary supplements, as well as in the herbs or foods that they are originally derived from. They are the subject of intensive investigations and new information is constantly being published. You may have come to this monograph via a herb that contains flavonoids. Note that the information in this general monograph relates to the individual flavonoids, and the reader is referred back to the herb (and vice versa) where appropriate. It is very difficult to confidently predict whether a herb that contains one of the flavonoids mentioned will interact in the same way. The levels of the flavonoid in the particular herb can vary a great deal between specimens, related species, extracts and brands, and it is important to take this into account when viewing the interactions described below. Types, sources and related compounds Flavonoids are a very large family of polyphenolic compounds synthesised by plants that are common and widely distributed. With the exception of the flavanols (e.g. catechins) and their polymers, the proanthocyanidins, they usually occur naturally bound to one or more sugar molecules Read more […]