Antihistamines

Antihistamines seem to be known by everyone whether they have allergies or not. They are heavily advertised. And millions and millions of people take them everyday for various types of allergies. Unfortunately, this drug is often misused in the treatment of colds and allergies.

For most people, it is considered the drug of choice in the fight against seasonal allergies. They are often less expensive than topical nasal steroid sprays. These sprays don't relieve symptoms in the eyes like antihistamines do. And many of the seasonal airborne allergens that affect our nasal passages also affect our eyes.

The thing to watch out for is the tolerance that it produces. At first, they may make you feel sleepy. Later, with continued use, they might not do so. At first glance, this may seem to be a positive. However, the other side is that they may no longer be as effective. Switching to a different kind may be recommended by your doctor when this happens.

With the many studies that have been conducted on this drug, it has been shown to be effective in most studies for:

• various forms of hay fever
• hives
• allergic conjunctivitis (eye allergies)
• used in treatment of anaphylaxis (along with other medications such as epinephrine).

In order to understand what antihistamines do and how they work, we need to understand what histamine does so we know what it is that it is trying to prevent. Histamine is an important factor in the allergic reaction.

Histamine Explained

Histamine is a chemical produced by the body. It is important for our sleep and being awake. It helps to stimulate stomach acids and it is necessary for the production of mucus. It is a chemical that our body produces and is necessary for our good health.

Unfortunately, the release of too much (at one time) produces in us what we know as allergy symptoms. This is how many of us have come to know about histamine.

When mast cells or basophil cells burst open during an allergic reaction, a lot of chemicals along with histamine is released.

Histamine travels through the body looking for specific receptors on cells that are able to receive them. The body has many different kinds of receptors. Those involve with nasal allergies are known as H1 receptors.

When the inflammatory chemicals reach the H1 receptors, they cause the following conditions:

• Blood vessels become more permeable. They allow leakage into the surrounding tissue.
• Itchiness occurs from the irritation on nerve endings.
• Smooth muscles get smaller (contract).
• Blood flow increase and affected areas turn red and swell.

How Antihistamines Works

For histamine to produce allergy symptoms, it has to be able to connect with the receptors on cells. The histamine and the receptor fits much like a lock and key does. Antihistamine has a molecular structure very similar to histamine. Thus, they can connect with the same receptors.

Antihistamine works by getting to the receptor on the cells before the histamine. This leaves no place for the histamine to go. With the receptors being filled, the histamine is blocked from reaching its destination. Without being able to connect to the receptor on the cells, histamine cannot start the process of producing allergy symptoms.

They are most effective if taken before the body releases histamine from the mast cells. This is because allergy symptoms are initiated when the histamine reaches the receptors on the cells.

On the other hand, if the histamine has already been released, then they are not very effective. They can't block the histamine if they have already reached their destination. They are not going to "knock out" the histamine from the receptor.

The best approach for treating allergic rhinitis is to begin taking antihistamines before the exposure to the allergen. Anticipating your need before the sneezing and sniffling starts is the most effective approach. To be really effective, continuous use is needed throughout the duration of the exposure.

Classification

Antihistamines generally fall into two broad categories:

• First generation: sedating and available over-the-counter.
• They penetrate into the blood stream and the central nervous system. As a result, they cause more side effects than the newer, second generation. Drowsiness is the predominant side effect. But they also cause dry mouth, constipation, and nervousness. They affect your coordination and concentration. These over-the-counter drugs are cheaper in cost than those available only by prescription.
• Second generation: non-sedating and available by a prescription.
• The improvement made in the second generation is the decrease in penetration into the central nervous system from the blood. This allows them to be effective without causing the drowsiness. Available only by prescription, they do not need to be taken as often as the first generation.

Sedation verses non-sedation can be both an advantage and disadvantage. Rest and sleep is important for the body to recover. Taking sedation medication at bedtime can help us fall asleep. On the other hand, drowsiness causing medication can be a problem in the daytime. Pilots, for example, are prohibited from using sedation medication 24 hours before a flight.

Most people are unaware of how sedating medication can affect their daily life. Driving while taking the drowsiness-causing medication can be dangerous to you and to the cars around you. These drugs do come with warnings about operating a vehicle and operating machinery.

Good or Bad?

As with most drugs, know the side effects and weigh the pros and cons. A few are mentioned below:

Advantages

• can block the effects of histamine.
• contributes to blocking the allergic reaction from occurring.
• helps in minimizing allergic symptoms.

Disadvantages

• drowsiness, sleepiness, or sluggishness. This can be an issue in our automobile-dependent society.
• cannot reduce swelling once it has occurred.
• the drying effect in the nose tends to thicken the mucus. This increases the risk of blocking the sinuses from draining. This will also inhibits the cilia from working properly.
• increases the effects of alcohol and further reduce a persons ability or coordination.
• causes dry eyes or mouth.
• can cloud your concentration.
• can slow your reaction time.
• rather than sleepiness, they can cause nervousness or insomnia in others.

Summary

Antihistamines competes with histamine for specific binding sites. By reaching the receptor sites before histamine, it leaves the histamine with no place to go.

The effectiveness of these drugs varies from person to person. And they are not very effective on the common cold because the common cold is caused by a virus. One kind that is effective in relieving symptoms for one person may be ineffective for another. Your physician can prescribe another type if you are not getting the type of relief that you are looking for.

If you would like more information, the FamilyDoctor.org has a good article on antihistamines. Remember, the pharmacist at your local store can be a great resource!

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