Fexofenadine is a second-generation antihistamine used to relieve allergy symptoms. It functions by selectively blocking peripheral histamine h1 receptors without crossing the blood-brain barrier. This receptor antagonism prevents histamine from binding to its sites and reduces the cascade of inflammatory signals that cause sneezing, itching, and rhinorrhea. The drug is metabolized minimally in the liver and is primarily excreted unchanged in the bile, contributing to its low systemic absorption. Its pharmacokinetic profile yields a prolonged duration of action allowing once-daily dosing for most patients. By limiting histamine activity in vascular and mucosal tissues the medication improves nasal airflow and reduces ocular irritation. Overall the compound provides symptomatic relief through competitive inhibition of histamine receptors and minimal central nervous system penetration.

Fexofenadine is a second-generation antihistamine used to relieve allergy symptoms such as sneezing, itching, and watery eyes. It works by blocking histamine h1 receptors on cells that trigger the allergic response. Unlike first-generation antihistamines it does not enter the brain easily, which reduces drowsiness. The drug is a metabolite of the prodrug terfenadine and is formed in the liver after oral administration. Its active form binds to the h1 receptor and prevents histamine from attaching, thereby stopping the cascade of allergic signs. After oral intake it is absorbed in the intestine, circulates in the bloodstream, and is eliminated mainly by the kidneys unchanged.

Headache is a frequently reported side effect of Fexofenadine. Dizziness may occur, especially when standing up quickly. Nausea or mild stomach discomfort can be experienced by some users. Fatigue or a feeling of low energy is occasionally noted. Dry mouth or a metallic taste sometimes appears. Rash or mild skin irritation may develop in rare cases. Swelling of the lips or tongue, though rare, may indicate a serious reaction.

Fexofenadine may cause drowsiness in some individuals and this effect is generally mild and infrequent. It can also lead to headache which typically resolves without intervention. Some users experience nausea that is usually transient and manageable. A sensation of fatigue may occur, especially when starting treatment. Dry mouth is reported occasionally but is not considered severe. Rarely, mild abdominal discomfort has been noted in clinical observations.