Antihistamine.

An antihistamine is an over the counter medicine available (mostly tablets are used) without prescription  usually taken as an anti allergy pill to treat allergy, itching, hay fever, common cold, itching and watery eyes, chest congestion. It is also used to induce sleep.

How Antihistamines Work.

• For Insomnia. Antihistamines block the action of histamine,  a chemical messenger of the brain which promotes wakefulness. By this action, antihistamines promote sleep. Though they produce drowsiness, they should not be taken if you have chronic insomnia. Antihistamines are more sedating than some hypnotics.
• For Allergy. Histamines are part of the body’s defense system which is released as part of the body’s reaction to a foreign substance called the allergen. This released histamine binds to the histamine receptors causing a chain reaction which results in increased blood flow to the concerned area and release of certain other chemicals which give rise to the allergic response such as itching. Antihistamines block the histamines receptors and prevent the chain reaction which causes the allergic responses such as itching.

Uses of Antihistamines.

Antihistamines are used to relieve allergy symptoms such as itching associated with  hives, insect bite, hay fever, eczema. It is also used to treat allergic bronchitis and cold which may be due to allergic substances. Itching of allergy is worse in the evening and night and are therefore advised to be taken at night. Daytime dose is usually avoided because of the drowsiness that these medicines cause. Antihistamines are available as tablets, syrups, eye drops, nasal sprays and creams.

List of Antihistamines and Brands.

Commonly used antihistamines include diphenhydramine (Benadryl) and doxylamine (Unisom). Diphenhydramine is the only antihistamine that is considered safe by the Food and Drug Administration.

Contraindications.

Antihistamines (such as Diphenhydramine and Doxylamine)  are contraindicated in the following conditions as their safety is not established and can cause harm.

• During pregnancy and lactation -can harm the development of the fetus.
• In children under the age of 12 years.
• When other sedatives are being used.
• When you have consumed alcohol, antihistamines can add to the sedative effect of alcohol.
• In patients who have a history of heart disease, glaucoma, asthma, peptic ulcer  and enlarged prostrate as symptoms of these diseases may worsen.
• These medicines should not be used when alertness is required such as when driving or operating machinery.

Side Effects of Antihistamines.

• Drowsiness during the next day.
• Dryness of mouth, throat or nose.
• Decreased memory.
• Confusion.
• Muscle weakness.
• Tremors.
• Stomach problems.

Types of Antihistamines.

There the old types of antihistamines which enter the brain and cause drowsiness and the new type which do not cause drowsiness.

Examples of the old type include promethazine (Phenergan), hydroxyzine (Atarax), or alimemazine (Vallergan).

Examples of new non drowsy antihistamines which do not cause drowsiness are cetirizine and loratadine. They are however not effective in controlling the severe itching of eczema.

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