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.
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.
The difference between them is really blurred." "Under some circumstances, the nonsedating formulas do cause sedation and in some cases, these sedating formulas do not," he tells Web MD.
"In some studies we reviewed, some people actually experienced more sedation with the newer, nonsedating formulas than with the older, sedating products.
" April 25, 2003 -- Timely research for the start of hay fever season: Despite their higher cost, the newer, so-called "second generation" of more expensive "nonsedating" prescription antihistamines may be no more effective at preventing fatigue and memory lapses than older over-the-counter formulas such as Benadryl.
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.