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.
Histamine-1 receptors are located in the airways, blood vessels and gastrointestinal tract (stomach and esophagus).
Stimulation of these receptors can lead to conditions such as a skin rash or inflammation, a narrowing of the airways (bronchoconstriction), hay fever, or motion sickness.
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.
It is not advised to prescribe a sedating a H1-antihistamine to infants because, although this is not documented, it could increase the risk of sudden death.Antihistamines are inhibitors of histamine receptors. H1-antihistamines, inhibit competitively H1 receptors and the corresponding effects i. They do not inhibit antigen/antibodies reactions, nor histamine release, they inhibit H1 effects. H1-antihistamines have been used for more than fifty years in treating various allergic manifestations. H1-antihistamines which penetrate into brain elicit, by inhibiting stimulant effect of histamine, drowsiness.Histamine-1 receptors are also found in the brain and spinal cord, and stimulation of these receptors makes you more awake and alert.Sedating antihistamines oppose the effects of histamine on H1 receptors in your brain, which is why they cause sedation and drowsiness.