I always thought that Dramamine was first generation, and Benadryl. Chlorpheniramine and Dex, and bromo were 2nd, and
the new ones like Claritin, Allegra 3rd. Back when the pheniramines were advertised and promoted, they were suggested as "less drowsy" than Benadryl and Atarax tended to be.
But some places list them differently.
The distinction is that only a few have little or no CNS effects and are the most recent. Things like Zyrtec contain some drowsiness factors and really aren't 3rd generation, IMO.
Allegra is the metabolite of Seldane, and works pretty well with little or no CNS effects. Claritin is overused, and useless IMO.
We used to get RXs from doctors using it themselves, taking 2 or 3 a day to try and get some effects!
Here is one example:
http://www.ncbi.nlm.nih.gov/pubmed/15992014
Quote:
Expert Opin Investig Drugs. 1998 Jul;7(7):1045-54.
Therapeutic advantages of third generation antihistamines.
Handley DA1, Magnetti A, Higgins AJ.
Author information
Abstract
A third generation of antihistamines is emerging for the treatment of allergic rhinitis and chronic urticaria. First generation antihistamines are among the most widely used drugs in the world, and provide symptomatic relief from allergies and the common cold to millions of patients, mainly in OTC combination preparations. Their full potential is limited by the sedation caused by their effects on histamine receptors in the brain. Second generation antihistamines (terfenadine, astemizole, loratadine and cetirizine), which block peripheral H1 receptors without penetrating the blood-brain barrier, were developed and introduced from 1981 onwards to provide comparable therapeutic benefit without the CNS side-effects. Although largely successful in this goal, terfenadine and astemizole were found to cause potentially serious arrhythmias when plasma concentrations became elevated subsequent to impaired metabolism. It was established that the cardiac toxicity was mainly due to the parent drugs. As active metabolites could account for most of the clinical benefit, the goal for the third generation of antihistamines became to develop therapeutically active metabolites that were devoid of cardiac toxicity. The first of these drugs, fexofenadine (the active metabolite of terfenadine), was approved in July 1996, after an unusually rapid development programme. Its introduction set a new standard of safety that led the FDA to request the withdrawal of terfenadine in 1997 on the grounds that a safer version of an equivalent drug was now available. Norastemizole and descarboethoxy loratadine, the metabolites of astemizole and loratadine, respectively, are also in clinical development. These offer comparable or superior clinical benefits.
PMID:
15992014
[PubMed]
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