Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines; other agents may have antihistaminergic action but are not true antihistamines.In common use, the term "antihistamine" refers only to H In type I hypersensitivity allergic reactions, an allergen (a type of antigen) interacts with and cross-links surface Ig E antibodies on mast cells and basophils.Examples of sedating antihistamines: Sedation is rare with non-sedating antihistamines, however patients should be made aware that a sedative effect may occur and performance of skilled tasks such as operating machinery or driving maybe affected.People with lamellar and other forms of ichthyosis are unable to sweat normally and often develop itching, or “pruritus,” in hot, humid weather or when otherwise overheated by exercise, sunlight, or by overdressing in warm clothes.The reason for this inability to sweat normally is that the excessive skin scale clogs the pores of the sweat glands and traps the sweat.The trapped sweat irritates the skin, leading to itchiness, redness, and occasionally small blisters.Most of the studies reviewed used doses that were twice the recommended amount -- 50 milligrams -- of diphenhydramine, the active ingredient in Benadryl and other first-generation "sedating" allergy medications."We're not saying that there's not a difference," says lead researcher Bruce G.
So concludes a new study published in the current issue of Journal of Allergy and Clinical Immunology in which researchers compared 18 previous trials investigating antihistamine-caused sedation levels in 1,500 people between ages 8 and 81.
The drugs of the first antihistamine generation are: promethazine, alimemazine, dexchlorpheniramine, brompheniramine, buclizine, carbinoxamine and doxylamine, are sedating and elicit a drowsiness which can be awkward.
The first-genaration antihistamines have alpha adrenolytic activity which can decrease the vasoconstrictive effect of adrenaline and noradrenaline and an antimuscarinic effect with the corresponding adverse effects.
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.