Allermed Mechanism of Action

Pharmacology: Cetirizine hydrochloride is a long-acting antihistamine causing little or no drowsiness. It does not demonstrate any antimuscarinic activity. This drug competes reversibly with histamines which are released from mast cells. Once bound to H₁ receptor sites in the tissues, cetirizine inhibits histamine-induced allergic reactions by blocking eosinophil infiltration to the site of allergen-induced cutaneous reactions.
Pharmacokinetics: Upon oral administration, cetirizine hydrochloride is rapidly absorbed from the gastrointestinal tract. Peak plasma concentration (C_max) is achieved after an hour. C_max of the drug may be delayed by food. However, it does not change the amount of drug absorbed. It has higher affinity to peripheral rather than central histamine H₁ receptors and does not penetrate the blood-brain barrier to a significant extent.
Cetirizine hydrochloride is highly protein bound (93%) and has a half life of approximately 11 hours in adults. This is mainly excreted in the urine as unchanged drug.
Cetirizine has been detected in breast milk.