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What is Levocetirizine and explain in detail?
Levocetirizine, sold under the brand name Xyzal among others, is a second-generation antihistamine used for the treatment of allergic rhinitis (hay fever) and long term hives of unclear cause. It is less sedating than older antihistamines. It is taken by mouth.Common side effects include sleepiness, dry mouth, cough, vomiting, and diarrhea. Use in pregnancy appears safe but has not been well studied and use when breastfeeding is of unclear safety. It is classified as a second-generation antihistamine and works by blocking histamine H1-receptors.Levocetirizine was approved for medical use in the United States in 2007. It is available as a generic medication. In 2019, it was the 193rd most commonly prescribed medication in the United States, with more than 2 million prescriptions.

Medical uses
Levocetirizine is used for allergic rhinitis. This includes allergy symptoms such as watery eyes, runny nose, sneezing, hives, and itching.

Side effects
Levocetirizine is referred to as a non-sedating antihistamine as it does not enter the brain in significant amounts and is therefore unlikely to cause drowsiness. Cardiac safety with repolarization may be better than some other antihistamines, as levocetirizine does not significantly prolong the QT interval in healthy individuals. However, some people may still experience some slight sleepiness, headache, mouth dryness, lightheadedness, vision problems (mainly blurred vision), palpitations and fatigue.

Pharmacology
Levocetirizine is an antihistamine. It acts as an inverse agonist that decreases activity at histamine H1 receptors. This in turn prevents the release of other allergy chemicals and increases the blood supply to the area, providing relief from the typical symptoms of hay fever. Levocetirizine, (R)-(-)-cetirizine, is essentially a chiral switch of (±)-cetirizine. This enantiomer, the eutomer, is more selective and less sedative and the (S)-counterpart, the distomer, is inactive.

Chemistry
Chemically, levocetirizine is the active levorotary enantiomer of cetirizine, also called the l-enantiomer of cetirizine