Allerzet Mechanism of Action

Pharmacology: Pharmacodynamics: Levocetirizine, the active enantiomer of cetirizine, is a second generation antihistamine.
It selectively antagonizes histamine H₁-receptors. In vitro studies have shown that levocetirizine has twice the H₁-receptor affinity of cetirizine.
Levocetirizine (at half of cetirizine dosage) appears to be as potent as cetirizine in inhibiting histamine-induced sneezing, increased nasal airway resistance, and skin wheal and flare.
Compared with other antihistamines (e.g., desloratadine, fexofenadine, loratadine), it exhibits greater and more consistent inhibition of histamine-induced wheal and flare.
Pharmacokinetics: Levocetirizine is rapidly and extensively absorbed after oral administration. Peak plasma concentrations are seen at 0.5 hour for oral solution and 0.9 hour for tablets following oral administration. Food has no effect on the extent of exposure of levocetirizine, but time to peak plasma concentration is delayed by approximately 1.25 hours and peak plasma concentration is decreased by approximately 36% after administration with a high fat meal. Levocetirizine can, therefore, be administered with or without food.
No tissue distribution data are available in humans, neither concerning the passage of levocetirizine through the blood-brain barrier. Levocetirizine is 90% bound to plasma proteins. The apparent volume of distribution is approximately 0.4 L/kg.
In humans, the extent of levocetirizine metabolism is less than 14% of the dose. Therefore, differences resulting from genetic polymorphism or concomitant intake of enzyme inhibitors are expected to be negligible. Metabolic pathways include aromatic oxidation, N- and O-dealkylation, and taurine conjugation. Due to its low metabolism and absence of metabolic inhibition potential, the interaction of levocetirizine with other substances, or vice-versa, is unlikely.
The plasma elimination half-life of levocetirizine is approximately 8 to 9 hours following oral administration. Mean oral total body clearance is approximately 0.63 mL/kg/min. The major route of excretion of levocetirizine and its metabolites is via urine, accounting for a mean of 85.4% of the dose. Excretion via feces accounts for only 12.9% of the dose. Levocetirizine is excreted both by glomerular filtration and active tubular secretion.
Special Population: Renal Impairment: The area under the plasma concentration-time curve (AUC) is increased by 1.8-, 3.2-, 4.3-, or 5.7-fold in those with mild, moderate, severe impairment, or end-stage renal disease, respectively. The corresponding increases of half-life estimates were 1.4-, 2.0-, 2.9-, and 4-fold, respectively.