Over-the-Counter Drugs - Antihistamines and allergy drugs

Over The Counter Drugs Antihistamines And Allergy Drugs 2748
Photo by: Dmitry Kalinovsky

The body's immune system protects the body from sickness and infection. To do so it must recognize and respond to any foreign substance it encounters. Histamine is an organic substance that plays an important role in the human body's response to injury or invasion. When an injury or allergic reaction occurs, the body releases histamine in response. An allergic reaction occurs when the immune system responds aggressively to a foreign substance. There are two main types of allergies; each is triggered by different substances. Perennial (year-round) allergies are usually a reaction to things such as animal dander, paint fumes, certain foods, drugs, dyes, or chemicals. Seasonal (occurring at certain times of the year) allergies are generally environmental. They are a reaction to pollens, trees, grass, ragweed, and mold spores.

Antihistamine drugs used to treat allergies are called H1 blockers because they only block histamine on H1 receptors. H1 receptors are found mostly in the small blood vessels in the skin, nose and eyes. High levels of histamine in these receptors cause an allergic reaction, usually in the way of a stuffy nose or sneezing. Allergic reactions may include itching or swelling skin such as hives, eczema, itching from insect bites, or irritation of the eyes. Antihistamines are synthetic (human-made) drugs that block the action of histamine by replacing it at one of two sites where it binds to the receptor, which prevents reactions from occurring. This reduces the irritation in the eyes and nose, congestion and breathlessness in the lungs, and redness, itching, or swelling of the skin.

Antihistamines also pass from the blood to the brain where they cause general sedation (drowsiness) and depression of certain brain functions, such as the vomiting and coughing mechanisms. Since most antihistamines have this sedative effect on the brain, they are often used in sleep aid drugs (see section on sleep aids). They are also used to control nausea and motion sickness.


Some people may know that drinking grapefruit juice when taking medication can help with the body's absorption of certain drugs. But a recent study at the University of California at San Francisco has shown that in some cases, grapefruit juice may actually decrease the absorption of drugs.

Grapefruit juice increases absorption of drugs by reducing the level of an intestinal enzyme known as CYP3A4. This enzyme breaks down drug molecules before they reach the bloodstream. A University of California study, however, found that an unknown substance in grapefruit juice activates a mechanism in the intestinal tract increasing the likelihood that certain drugs will not enter the bloodstream. Some of the drugs affected by this mechanism are those used to combat cancer, treat congestive heart failure, suppress organ rejection after a transplant, control high blood pressure, and treat allergy symptoms.

Depending on the drug, grapefruit juice may either increase or decrease levels of the drug in the bloodstream; thus, people may get too much or too little medication, both of which could be dangerous situations. In most cases, doctors recommend that people avoid taking drugs with grapefruit juice until more is known about how it affects drug absorption.

Some experts believe that antihistamines should not be available over the counter because of the drowsiness and sluggishness that is associated with their consumption. Other side effects include blurred vision, dry mouth, constipation, and light-headedness (all of which are particularly prominent in elderly users). Pregnant women and sufferers of chronic bronchitis, emphysema, and glaucoma should avoid antihistamines. Like many drugs, most antihistamines should not be taken with alcohol, antidepressants, or sedatives.

Antihistamines are not usually helpful in treating the common cold. They are sometimes used to treat fever, rash, and breathing problems that result from reactions to blood transfusions, and allergic reactions to drugs. Anti-histamines containing diphenhydramine are sometimes used in the early stages of Parkinson's disease.

These drugs should not be used for longer than seven days or by children under the age of six. Avoiding the substances that cause allergic reactions is usually the best treatment for allergies, when possible. If OTC allergy drugs do not help alleviate symptoms, allergy shots administered by a physician may be a viable alternative.


The lining of the nasal (nose) passages is called the mucous membrane. When infection, such as a cold or an allergic reaction, occurs, the blood vessels that supply the mucous membrane become enlarged and the mucous membrane swells. Fluid accumulates in nearby body tissue and mucus (the sticky substance secreted by the mucous membrane) is produced in larger amounts than usual. The result is a stuffy nose. Decongestants relieve a stuffy nose by limiting the production of mucus and reducing the swelling in the mucous membrane by constricting the blood vessels in the nose. This opens the airways and promotes drainage of nasal passages.

There are two types of decongestants: topical (applied to the body) and oral (taken by mouth). Topical decongestants are sprays or drops that are used directly in the nose, such as Neosenephrine. There are short- and long-acting topical decongestants that can provide relief from four to twelve hours; they usually start to work within a few minutes. Topical decongestants should not be used for more than three days because there is a risk of developing a problem called rebound congestion. When a person stops using a topical decongestant after using it for longer than recommended, the blood vessels in the mucous membrane will suddenly widen because they are no longer constricted by the drug. This causes congestion to occur all over again.

Oral decongestants, such as Drixoral, are taken through the mouth. Their effects are usually longer lasting than those of topical decongestants but they also take longer to yield noticeable relief. They are also more likely to cause side effects, such as increased heart rate and trembling, than topical decongestants. Both topical and oral decongestants should be used only by adults or children over the age of twelve unless advised by a doctor.

People with high blood pressure, diabetes, heart disease or an overactive thyroid should only use decongestants with their physician's approval. If a

Decongestant nose drops help clear stuffed nasal passages on contact. (Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission.)
Decongestant nose drops help clear stuffed nasal passages on contact. (Photograph by
Robert J. Huffman. Field Mark Publications
. Reproduced by permission.)

person uses decongestants too frequently, she or he may develop problems, such as nervousness, insomnia, dizziness, headaches, or palpitations.

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