Loratadine Classification
Loratadine is a second-generation, nonsedating histamine H1-receptor antagonist 1.
Key Distinguishing Features
Second-Generation H1 Antihistamine Characteristics
Loratadine belongs to the class of peripheral-selective H1-receptor antagonists that differ fundamentally from first-generation antihistamines 2:
- Nonsedating at recommended doses: Loratadine does not cause sedation when used at standard therapeutic doses (10 mg once daily), unlike first-generation antihistamines such as diphenhydramine or chlorpheniramine 2
- Peripheral selectivity: Loratadine demonstrates approximately 10-fold greater potency against peripheral H1 receptors compared to central nervous system H1 receptors, indicating poor blood-brain barrier penetration 3
- Minimal anticholinergic effects: Unlike first-generation agents, loratadine lacks significant anticholinergic side effects (no dry mouth, urinary retention, or constipation) 4, 5
Pharmacological Profile
The FDA labels loratadine specifically as an antihistamine 6, and clinical guidelines consistently classify it among the nonsedating H1 antihistamines licensed for once-daily dosing 1.
Important clinical distinction: While loratadine may cause sedation at doses exceeding the recommended dose, it does not cause sedation at the standard 10 mg daily dose 2. This contrasts with cetirizine (another second-generation agent), which may cause sedation even at recommended doses.
Additional Properties
Beyond H1-receptor antagonism, loratadine demonstrates "antiallergic" effects on mast-cell mediator release, particularly at higher doses 1. This provides additional therapeutic benefit beyond simple histamine receptor blockade.
Clinical Context
Loratadine is classified as a long-acting antihistamine with high selectivity for peripheral H1 receptors 7. Its active metabolite is desloratadine, which has an even longer elimination half-life (27 hours) 1.