All second generation antihistamines tested, significantly increased net accumulation of [3H]-colchicine to a level similar to that caused by the Pgp inhibitor verapamil.
By contrast, the first generation antihistamines showed no affinity for Pgp.
Ive heard that second generation antihistamines are nonsedating because they dont cross the blood brain barrier. Or is this just a assumption based on not feeling drowsy after.
Abstract First generation H1 receptor antagonists are often associated with adverse CNS effects such as sedation, whereas modem, second generation antihistamines are generally non-sedating.
Cetirizine was significantly more likely than loratadine to cause drowsiness and have a negative effect on motivation in one study of 60 patients with allergic rhinitis. Trials have shown both Zyrtec and Claritin are significantly more effective than placebo (a pretend pill) for reducing symptoms associated with allergic rhinitis, hay fever, and other allergies.
Trials have not consistently shown that one antihistamine is more effective than another, although one trial did report cetirizine reducing symptoms to a greater extent.
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Mechanism of Action Desloratadine is a long-acting tricyclic histamine antagonist with selective H1-receptor histamine antagonist activity.Histamines attach to the cells in your body and cause them to swell and leak fluid.This can cause itching, sneezing, runny nose, and watery eyes.The results indicate that differences in the ability of classical and modern antihistamines to interact with Pgp at the BBB may determine their CNS penetration and as a consequence the presence or absence of central side-effects.Abstract Background: Antihistamines are among the most frequently used medications in the United States. Two types of OTC antihistamines are available: first-generation and second-generation antihistamines. First-generation antihistamines are also sometimes used in OTC medicines.When your body is exposed to allergens, it releases histamines.Results of a radiolabeled tissue distribution study in rats and a radioligand H1-receptor binding study in guinea pigs showed that desloratadine did not readily cross the blood brain barrier. Dosing: Oral: Children: 6-11 months: 1 mg once daily 12 months to 5 years: 1.25 mg once daily 6-11 years: 2.5 mg once daily Children /= 12 years and Adults: 5 mg once daily Supplied Syrup (Clarinex®): 0.5 mg/m L (480 m L) [bubble gum flavor] Tablet (Clarinex®): 5 mg Tablet, orally-disintegrating (Clarinex® Redi Tabs®): 5 mg [contains phenylalanine 1.75 mg/tablet] Adult (usual) Chronic idiopathic urticaria: 60 mg orally twice daily.Seasonal allergic rhinitis: 60 mg orally twice daily or 180 mg once daily.We have tested the hypothesis that non-sedating antihistamines fail to enter the CNS due to recognition by the P-glycoprotein (Pgp) drug efflux pump expressed on the luminal surface of cerebral endothelial cells forming the BBB in vivo.The ability of several sedating and non-sedating antihistamines to affect the uptake of the Pgp model substrate [3H]-colchicine was examined using the immortalised rat brain endothelial cell line, RBE4, an established in vitro model of the BBB expressing Pep.