Pharmaniaga Loratadine Mechanism of Action

Loratadine is a long-acting tricyclic antihistamine with selective peripheral histamine H₁-receptor antagonistic activity. It is a piperidine derivative related to azatadine and has little central sedative or antimuscarinic activity.
Loratadine is rapidly absorbed from the gastro-intestinal tract after oral administration, peak plasma concentrations being attained in about one hour. Bioavailability is increased and time to peak plasma concentrations is delayed when administered with food. Loratadine undergoes extensive metabolism. The major metabolite, descarbo-ethoxyloratadine has potent histamine-H₁ blocking activity. Reported half-lives for loratadine and descarbo-ethoxyloratadine are 12 and 18 hours respectively. Loratadine is about 98% bound to plasma proteins; descarbo-ethoxyloratadine is less extensively bound. Loratadine and its metabolites have been detected in breast milk, but do not appear to cross the blood brain barrier to a significant extent. Loratadine and its metabolites are excreted in the urine and faeces.