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: 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 […]


ANGIOTENSIN RECEPTOR ANTAGONISTS act principally at the AT1 and/or AT2 receptors (see ANGIOTENSIN receptor AGONISTS). The first antagonists were derived in the early 1970s by substitutions within the angiotensin sequence. Saralasin ((Sar1,Ala8]-AII) blocks at both AT, and AT2 receptors, and is quite active experimentally, but is not stable in the body and was not used clinically. The first nonpeptide antagonists, announced in the early 1980s, were imidazole-5-acetic acid derivatives (e.g. S 8307 and S 8308), and acted as lead compounds from which stepwise modifications (through EXP 6155. EXP 6803, EXP 7711) led to orally active agents. The first of these registered for clinical usage (in 1995 in the UK and USA) was losartan, which can be used as an ANTIHYPERTENSIVE. This, and several other nonpeptide antagonists under clinical development, are more active at AT, receptors. Examples include candesartan, eprosartan, irbesartan, telmisartan. valsartan and zolasartan. There is currently little incentive to develop drugs that work by blocking angiotensin AT2 receptors since the role of these in body function is not clear. Nevertheless, there are experimental agents that act at both receptors (e.g. saralasin and others Read more […]


ANGIOTENSIN RECEPTOR AGONISTS are a family of potent agents with notable actions on the cardiovascular system and electrolyte balance, but have many other possible pathophysiological functions, including a putative central neurotransmitter role. The peptides are normally formed from a precursor molecule — angiotensinogen — an α2-globulin in the blood, by the action of a 340 amino acid glycoprotein called renin, which acts as an aspartyl protease enzyme (see RENIN INHIBITORS). Renin, and its precursor protein, are both stored in the juxtaglomerular cells of the kidney, and release is controlled by three different pathways within the kidney sensitive to Na+-transport, blood vessel stretch and β1-adrenoceptor activation, respectively. Overall, activation of the renin-angiotensin systems is hypertensive, but serves to increase renal perfusion. The relationships and actions of the members of the angiotensin peptides formed within the body pathways is complex. Cleavage of angiotensinogen initially forms the decapeptide angiotensin I (AI), which has little cardiovascular potency, but is immediately converted to an octapeptide, angiotensin II, through the C-terminal deletion of two residues, by angiotensin-converting Read more […]


ANTIHYPERTENSIVE AGENTS are used to reduce high blood pressure when it is raised in disease, though such drugs are not necessarily hypotensive (i.e. they may not lower blood pressure in normotensive subjects). Hypertension is an elevation of arterial blood pressure above the normal range expected in a particular age group, sex etc. It can have several different causes, which to some extent determine the treatment. Above certain values, after making lifestyle corrections, intervention with drug therapy may reduce the risk of heart attacks, kidney failure or a stroke, and may help in the treatment of angina pectoris. There are several large groups of drugs used as antihypertensives, each with a specific mode of action. DIURETICS are in common use as antihypertensives, and often a mild diuretic may be all that is required: e.g. amiloride. chtorothiazide, ethacrynic acid, frusemide, hydrochlorothiazide, spironolactone, triamterene. Beta-blockers, of which there are many, may be used if further treatment is necessary, with or without simultaneous administration of a diuretic: e.g. acebutolol, oxprenolol, propranolol and sotalol. See β-ADRENOCEPTOR ANTAGONISTS. Other antihypertensive drugs work as antisympathetic Read more […]