Drugs online research references
Clin Exp Allergy. 1990 May;20(3):269-72.
Does reversed-type anaphylaxis in healthy subjects mimic a real allergic reaction?
Henocq E, Rihoux JP.
Rue Beaujon, Paris, France.
Immediate and late cutaneous reactions were induced in healthy and atopic subjects by anti-IgE challenge and a skin-window technique was used in order to verify if the pattern of cells observed at 24 hr was similar in both groups. The study was first performed under basal conditions, and in a second double-blind cross-over step, it was performed again during treatment with cetirizine 10 mg b.i.d. and terfenadine 60 mg b.i.d. Anti-IgE challenge was followed by a significant eosinophil accumulation in atopic subjects only. Cetirizine significantly inhibited this phenomenon while terfenadine showed a mild non-significant inhibitory effect.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1973069&dopt=Abstract
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J Allergy Clin Immunol. 1990 Oct;86(4 Pt 2):606-12.
Pharmacology of antihistamines.
Woodward JK.
Merrell Dow Research Institute, Merrell Dow Pharmaceuticals Inc., Cincinnati, OH 45215.
Unlike the classic antihistamines, the new H1-receptor antagonists do not block cholinergic or central H1 receptors and thus do not produce the side effects, such as sedation, impaired psychomotor performance, and excessive mucosal drying, that are commonly associated with the older agents. Important pharmacokinetic and pharmacodynamic differences that exist among this class of antihistamines translate into varying pharmacologic effectiveness. Terfenadine, loratadine, and cetirizine are all rapidly absorbed in healthy and allergic volunteers (peak plasma levels, 2 to 5 hours); astemizole, however, has an initial distribution phase of 2 to 3 days. Further, astemizole has the longest time to relief of symptoms in this class; histamine wheal inhibition is not apparent until the second day of 10 mg dosing and does not peak for 9 to 12 days. In comparison, terfenadine's antihistaminic action peaks at 3 to 4 hours, loratadine's at 4 to 6 hours, and cetirizine's at 4 to 10 hours. However, whereas the recommended dose of loratadine (10 mg) confers 50% wheal inhibition, 60 mg terfenadine produces an 85% to 90% inhibition. In addition, loratadine and cetrizine have apparent dose-related sedative effects.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1977782&dopt=Abstract
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J Allergy Clin Immunol. 1990 Dec;86(6 Pt 2):1025-8.
Cetirizine: actions on neurotransmitter receptors.
Snowman AM, Snyder SH.
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2105.
First-generation H1-antagonist antihistamines, such as hydroxyzine, have the ability to cross the blood-brain barrier and cause sedation, which limits their usefulness in the treatment of allergic disorders. Cetirizine, a carboxylated metabolite of hydroxyzine, possesses the parent compound's antihistaminic activity but causes less sedation. We compared the activity of cetirizine at central H1 sites with that of hydroxyzine and terfenadine. We also compared the ability of cetirizine and three antihistamines to cross the blood-brain barrier. In each case we found that the drug's potency at H1 receptors in the central nervous system was similar to its activity in displacing H1 receptors in the lung. However, the selectivity for H1 receptors varied widely from drug to drug. Cetirizine did not bind at any of the receptors investigated, except H1 sites, even at concentrations as high as 10 mumol/L. Hydroxyzine and dexchlorpheniramine and, to a lesser extent, terfenadine crossed the blood-brain barrier in significant amounts. Cetirizine passed into the central nervous system only half as readily as terfenadine. These findings suggest that cetirizine's low incidence of sedative effects is most likely caused by its diminished potential to cross the blood-brain barrier and also may be partly the result of its greater selectivity for H1 receptors, compared with its effect at other receptors that may be involved in sedation.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1979798&dopt=Abstract
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