Common cold, histamine

Histamine is a potent vasodilator. It has various functions. It contracts the smooth muscles in the bronchi and gut and relaxes other muscles, such as those in the walls of fine blood vessels. Histamine is also responsible for the nasal congestion associated with common cold and allergic response to pollen. 

Antihistamines are used to alleviate allergic conditions such as rashes and runny eyes and nose and are decongestants that are used for swelled sinuses and nasal passages during the common cold. These symptoms are caused by histamine and hence the drugs that get rid of them are antihistamines. Antihistamines are also sleep inducers. 

Agents generally referred to as antihistamines are those that antagonize the action of histamine at H3 receptors. They act in a competitive manner and are primarily used in situations such as urticaria, hay fever, and insect bites. They are available for both local and oral administration. At the time of the development of the first antihistamines in the 1940s, they were hailed as the cure for the common cold. 

Antihistamines bind to the same active site of the enzyme that binds histamine in the cell, but they evoke a different response. An antihistamine like bFompheniramine, for example, inhibits vasodilation, so it is used to treat the symptoms of the common cold and allergies. Cimetidine (trade name Tagamet) is a histamine mimic that blocks the secretion of hydrochloric acid in the stomach, so it is used to treat individutils with ulcers. 

Hence, the treatment for the common cold remains largely palliative rather than curative. Administration of anti-inflammatory agents like aspirin, decongestants like ephedrine, and anti-histamines will relieve many of the symptoms without necessarily reducing the period of infection. The codeinelike drug dextromorphan is also used and this acts upon the A-methyl-D-aspartate (NMDA) receptors in the brain to increase the threshold for cough induction. One new experimental treatment involves the intranasal administration of ICAM-1 fragments to saturate the receptors. 

The combination possesses antihistamine/deconges-tant/anticholinergic properties. Chorpheniramine competitively antagonizes histamine at Hj-receptor sites phenylephrine stimulates postsynaptic alpha-receptors, resulting in vasoconstriction, which reduces congestion methscopolamine competitively inhibits action of acetylcholine at muscarinic receptors. The combination is indicated for temporary relief of symptoms of allergic rhinitis, casomotor rhinitis, sinusitis, and the common cold. 

Phenylephrine stimulates postsynaptic alpha receptors, resulting in vasoconstriction, which rednces nasal congestion. Chlorpheniramine competitively antagonizes histamine at Hi-receptor sites. They are indicated in the symptomatic relief of coryza and nasal congestion associated with common cold, sinusitis, allergic rhinitis, and other upper respiratory tract conditions. 

Prometh with codeine syrup 10 mg codeine phosphate and 6.25 mg promethazine hydrochloride) Promethazine competitively antagonizes histamine at H,-receptor sites and prodnces sedative as well as antiemetic effects. Codeine stimnlates opiate receptors in the CNS in addition to cansing respiratory depression, peripheral vasodilation, inhibition of intestinal peristalsis, stimulation of the chemoreceptors that cause vomiting, increased bladder tone, and suppression of cough. They are indicated in the temporary relief of coughs and upper respiratory tract symptoms associated with allergy or the common cold. 

A number of amines are vitamins. These include nicotinic acid and nicotinamide, pyridoxine (vitamin Be, see The Chemistry of... Pyridoxal Phosphate in WileyPLUS for Chapter 16), and thiamine chloride (vitamin B-, see The Chemistry of... Thiamine," in WileyPLUS for Chapter 17). Nicotine is a toxic alkaloid found in tobacco that makes smoking habit forming. Histamine, another toxic amine, is found bound to proteins in nearly all tissues of the body. Release of free histamine causes the symptoms associated with allergic reactions and the common cold. Chlorpheniramine, an antihistamine, is an ingredient of many over-the-counter cold remedies. 

First-generation antihistamines provide symptomatic relief from allergies and the common cold to patients. However, their therapeutic potential is hampered by the sedation caused by their effects on histamine receptors in the brain (1-3). Second-generation antihistamine (astemizole, as an example) block peripheral HI receptors were introduced to provide comparable therapeutic benefit without the CNS side effects under manufactures recommended doses (1-4). It was reported that astemizole was found to cause arrhythmias when drug exposures became... 

Release of free histamine causes the symptoms associated with allergic reactions and the common cold. Chlorpheniramine, an "antihistamine," is an ingredient of many over-the-counter cold remedies. 

In addition to airway inflammation, asthmatics commonly exhibit bronchial hyperreactivity. The concentration of a bronchial spasmogen (e.g., methacholine or histamine) needed to produce a 20% increase in airway resistance in asthmatics is often only 1-2% of the equally effective concentration in healthy control subjects. This bronchial hyperreactivity most often is nonspecific such that the airways are also inordinately reactive to stimuli such as strong odors, cold air, and pollutants. 

Vecuronium and atracurium. These are commonly used agenUs, Vecuronium has no cardiovascular effects. It depends on hepatic inactivation and recovery can occur within 20—30 minutes, making it an attractive drug for short procedures. Atracurium has a duration of action of 15-30 minutes. It is only stable when kept cold and at low pH. At body pH and temperature it decomposes spontaneously in plasma and llterefore does not depend on renal or hepatic function for its elimination. It is the drug of choice in patients with severe renal or hepatic disease. Atracurium may cause histamine release with flushing and hypotension. 

---