Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 18 Autocoids and Antihistamines

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Histamine  There are two types of histamine receptors. Histamine 1 receptors are involved with allergic response.  Histamine is released from mast cells when an allergic reaction occurs.  Histamine release causes vasodilation, increased capillary permeability, bronchoconstriction, and pain or itching in cutaneous nerve endings.  Stimulation of histamine 2 receptors is involved with increased gastric acid secretion. 2

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Adverse Reactions  Anaphylaxis is a major adverse reaction of histamine release.  It is characterized by difficulty in breathing, seizures, lapses into unconsciousness, and death.  Other symptoms include apprehension, paresthesia, urticaria, edema, choking, cyanosis, coughing, and wheezing.  Histamine is used in the diagnosis of achlorhydria and pheochromocytoma. 3

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Antihistamines  Antihistamines block histamine 1 receptors and are used to treat allergic rhinitis, allergic reaction, nausea and vomiting, and preoperative sedation.  Antihistamines can also be used as over-the- counter sleep aids, and as local anesthesia.  Antihistamines are categorized as either sedating or nonsedating. 4

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Antihistamines  Pharmacologic Effects  By blocking histamine response these drugs decrease capillary permeability.  Vascular smooth muscle dilation is also blocked.  These drugs cause bronchial relaxation.  They suppress pain and itching by blocking histamine actions at cutaneous nerve endings.  These drugs also cause sedation.  They have weak anticholinergic effects.  They have antiemetic and antimotion sickness effect.  They provide some local anesthetic effects. 5

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Sedating Antihistamines  Adverse reactions of antihistamines are the same as their pharmacologic effects.  The adverse reactions vary in relative amounts among the different drugs.  Sedation is the most common side effect of older antihistamines.  Dizziness, incoordination, and fatigue can occur.  Stimulation or excitement often occurs in children, the elderly, and in those who use high doses.  Some drugs can cause nausea, vomiting, and constipation.  Xerostomia often occurs with older drugs. 6

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Peripheral (Nonsedating) H 1 -Receptor Antagonists  These drugs do not cross the blood-brain barrier.  As a result they are less likely to cause sedation. 7

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Prostaglandins and Thromboxanes  They are members of a biologically active group of agents called eicosanoids.  They are found in most body tissues and fluids.  They are produced in the body in response to many different stimuli.  These agents can cause vascular smooth muscle relaxation or constriction depending on the specific prostaglandin released. 8

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Prostaglandins and Thromboxanes  Thromboxane stimulates platelet aggregation and prostaglandin 1 inhibits platelet aggregation.  Prostaglandins stimulate uterine contractions.  Prostaglandins stimulate the release of growth hormone, increase body temperature, and stimulate the release of female sex hormones. 9

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Prostaglandins and Thromboxanes  Prostaglandins have been implicated in periodontal disease.  They appear to have a role in the inflammation that is associated with periodontal disease.  Prostaglandins also prevent the synthesis of new bone by inhibiting osteoblastic activity. 10

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Other Autocoids  Leukotrienes  Leukotrienes are a group of autocoids derived from arachidonic acid.  They cause powerful bronchoconstriction.  They also contract the uterus and gastrointestinal tract.  Kinins  Kinins may play a role in dental disease.  Plasma kinins may be involved with shock and acute or chronic allergic or inflammatory conditions. 11

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Other Autocoids  Substance P  This peptide is thought to function as a neurotransmitter in the CNS and as a local hormone in the gastrointestinal tract.  It is a vasodilator and produces hypotension.  It causes secretion in the salivary glands.  It increases sodium and water excretion from the kidneys. 12