va substance that performs many functions. It is involved in nerve impulse transmission in the central nervous system (CNS), dilation of capillaries, contraction of smooth muscle, stimulation of gastric secretion, and acceleration of the heart rate. There are two types of cellular receptors for histamine. Histamine 1 (H1) receptors mediate smooth muscle contraction and dilation of capillaries; histamine 2 (H2) receptors mediate acceleration of the heart rate and gastric acid secretion. The release of excessive amounts of histamine can lead to anaphylaxis and severe allergic symptoms and may result in any or all of the following physiologic changes: • Constriction of smooth muscle, especially in the stomach and lungs • Increase in body secretions • Vasodilatation and increased capillary permeability, which results in the movement of fluid out of the blood vessels and into the tissues and thus causes a drop in blood pressure and edema Safety: Herbal Therapies and Dietary Supplements Echinacea (Echinacea) Overview The three species of echinacea used medicinally are Echinacea angustifolia, Echinacea pallida, and Echinacea purpurea. Echinacea has been shown in clinical trials to reduce cold symptoms and recovery time when taken early in the illness. This is believed to be due to its immunostimulant effects. At this time, there is no strong research evidence to warrant recommending the herb for urinary tract infections, wound healing, or prevention of colds; further study is needed to provide evidence of its therapeutic effects and indications. Common Uses Stimulation of the immune system, antisepsis, treatment of viral infections and influenza-like respiratory tract infections, promotion of wound healing, and chronic ulcerations Adverse Effects Dermatitis, upset stomach or vomiting, dizziness, headache, unpleasant taste Potential Drug Interactions Amiodarone, cyclosporine, phenytoin, methotrexate, ketoconazole, barbiturates; tolerance likely to develop if used for more than 8 weeks. Because some preparations have a high alcohol content, they may cause acetaldehyde syndrome with disulfiram (Antabuse) (see Chapter 17). Contraindications Contraindicated for patients with acquired immunodeficiency syndrome, tuberculosis, connective tissue diseases, multiple sclerosis 567 Safety: Herbal Therapies and Dietary Supplements Goldenseal (Hydrastis canadensis) Overview Goldenseal is found in wooded areas from the northeastern to midwestern United States. It is the dried root of the plant that is most commonly used. These components have been shown to have antibacterial, antifungal, and antiprotozoal activity. The alkaloid berberine has both anticholinergic and antihistaminic activity. Common Uses Treatment of upper respiratory tract infections, allergies, nasal congestion, and numerous genitourinary, skin, ophthalmic, and otic conditions Adverse Effects Gastrointestinal (GI) distress, emotional instability, mucosal ulceration (e.g., when used as a vaginal douche) Potential Drug Interactions Gastric acid suppressors (including antacids, histamine H2 blockers [e.g., ranitidine], proton pump inhibitors [e.g., omeprazole]): reduced effectiveness due to acid-promoting effect of herb Antihypertensives: reduced effectiveness due to vasoconstrictive activity of herb Contraindications Acute or chronic GI disorders; pregnancy (has uterine stimulant properties); should be used with caution by those with cardiovascular disease. Antihistamines are drugs that directly compete with histamine for specific receptor sites. For this reason, they are also called histamine antagonists. Antihistamines that compete with histamine for the H2 receptors are called H2 antagonists or H2 blockers and include cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), and nizatidine (Axid). Because they act on the gastrointestinal (GI) system, they are discussed in detail in Chapter 50. This chapter focuses on the H1 antagonists (also called H1 blockers); they are the drugs commonly known as antihistamines. They are very useful drugs, because approximately 10% to 20% of the general population is sensitive to various environmental allergens. Histamine is a major inflammatory mediator in many allergic disorders, such as allergic rhinitis (e.g., hay fever; mold and dust allergies), anaphylaxis, angioedema, drug fevers, insect bite reactions, pruritus (itching), and urticaria (hives). H1 antagonists include drugs such as diphenhydramine (Benadryl), chlorpheniramine (generic), fexofenadine (Allegra), loratadine (Claritin), and cetirizine (Zyrtec). They are of greatest value in the treatment of nasal allergies, particularly seasonal hay fever. They are also given to relieve the symptoms of the common cold, such as sneezing and runny nose. In this regard they are palliative, not curative; that is, they can help alleviate the symptoms of a cold but can do nothing to destroy the virus causing it. The clinical efficacy of the different antihistamines is very similar, although they have varying degrees of antihistaminic, anticholinergic, and sedating properties. The particular actions and indications for a particular antihistamine are determined by its specific chemical makeup. All antihistamines compete with histamine for the H1 receptors in the smooth muscle surrounding blood vessels and bronchioles. They also affect the secretions of the lacrimal, salivary, and respiratory mucosal glands, which are the primary anticholinergic actions of antihistamines. These drugs differ from each other in their potency and adverse effects, especially in the degree of drowsiness they produce. The antihistaminic, anticholinergic, and sedative properties of some of the more commonly used antihistamines are summarized in Figure 36-1. Because of their antihistaminic properties, they are indicated for the treatment of allergies. They are also useful for the treatment of problems such as vertigo, motion sickness, insomnia, and cough. Several classes of antihistamines are listed in Table 36-1, along with their various anticholinergic and sedative effects.