Loratadine is a classic, long-acting second-generation antihistamine designed for clean, non-drowsy systemic relief. Upon oral administration, it is metabolized by hepatic cytochrome P450 enzymes into its active form (desloratadine). It competitively blocks peripheral H1 receptors, preventing histamine from triggering sensory nerve irritation (sneezing/itching) and vascular leakage. Because of its large molecular structure and high affinity for peripheral tissues, it has negligible penetration into the central nervous system, keeping cognitive alertness completely unaffected during daily therapy.