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Antihistamines H1 Antagonists

H1-antihistamines have been used for more than fifty years in treating various allergic manifestations.  H1-antihistamines which penetrate into brain elicit drowsiness by inhibiting stimulant effect of histamine.

Antihistamines inhibit histamine receptors from responding to the stimulant affects of histamine such as drowsiness, vasodilation and capillary permeability.  They do not prevent  cell degranulation, and they do not inhibit antigen/antibodies reactions, nor histamine release, they inhibit H1 effects.

In addition to this antihistamine effect, they can have parallel pharmacological properties, for example antimuscarinic and adrenolytic effects which must be considered.

It is usual to classify H1-antihistamines into two classes: old ones, called first-generation agents, which are sedating and recent ones, called second-generation agents which have slight or no sedating effects because they do not cross the blood-brain barrier.

In addition, each compound can have or not have parallel properties, antimuscarinic effects for example. This distinction between generations must be taken with caution because a product considered as non sedative or not antimuscarinic can, in certain circumstances, large doses or particular susceptibility of the patient ,have these effects.

List of most common H1 Antagonist Antihistamines

Brompheniramine Diphenhydramine
Ceterizine Fexofenadine
Chlorpheniramine Hydroxizine
Clemastine Levoceterizine
Cyproheptadine Loratadine
Desoloratadine Promethazine

Urticaria Medication
First Generation H1 Blockers
First, Second and Third Generation H1 Blockers (Includes list of Antihistamines)

Clinical Trial Comparing Cyproheptadine and Chlorpheniramine

Nuggets of Wisdom

Yes, there is such a thing as having an allergic type reaction to temperatures. This is defined as a physical urticaria. Other physical urticarias include Solar, Aquagenic, Pressure, Vibration and Exercise.

Most reactions are pseudo-allergic. By definition, an allergy involves inhaling or consuming an allergen. Physical urticarias have no known allergen. Despite the terminology and medical definitions, systemic reactions can be life threatening.

Cold has an arbitrary definition based on an individual feeling. For a person with a cold urticaria, cold can be defined as any temperature cooler than their own body temperature.

You do not have to be cold to have a reaction to the cold; contact with cold can trigger a reaction.

You can have an allergic type reaction to both cold and heat simultaneously.

Most reactions considered anaphylactic are really anaphylactoid by definition.

Moving to a warmer climate as a treatment for Cold Urticaria is a myth. Warmer climates present their own issues for those with Cold Urticaria.

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