What does loratadine do?

Loratadine: Mechanism and Clinical Effects

Loratadine is a second-generation antihistamine that blocks peripheral histamine H1-receptors to effectively relieve symptoms of allergic rhinitis with minimal sedative effects at recommended doses. 1

Mechanism of Action

Loratadine works by:

• Selectively blocking peripheral histamine H1-receptors
• Demonstrating threefold greater affinity for peripheral vs. central H1-receptors 2
• Being metabolized to descarboethoxyloratadine, its active metabolite which is four times more potent than the parent drug 2

Clinical Effects

Loratadine effectively treats:

• Sneezing
• Nasal itching
• Rhinorrhea (runny nose)
• Itchy/burning eyes 3

However, it has:

• Limited effect on nasal congestion compared to other symptoms 1
• Less effectiveness for nonallergic rhinitis syndromes 1

Pharmacokinetics

• Onset of action: Within 1 hour 2
• Duration of action: At least 24 hours, allowing once-daily dosing 2
• Peak plasma concentration: 1-2 hours for parent drug, 3-4 hours for active metabolite 2
• Elimination half-life: Approximately 10 hours for loratadine, 20 hours for metabolite 2

Advantages Over First-Generation Antihistamines

Loratadine offers significant advantages over first-generation antihistamines:

• No sedation at recommended doses 1, 4
• No performance impairment at recommended doses 1
• No anticholinergic effects (dry mouth, urinary retention) 5
• No significant drug interactions reported 2

Clinical Efficacy

In clinical studies, loratadine (10mg once daily) has demonstrated:

• Superior efficacy to placebo 3
• Faster onset of action than astemizole 4, 6
• Comparable efficacy to terfenadine, clemastine, and other antihistamines 4, 6, 3
• 46% reduction in combined nasal and non-nasal symptoms from baseline 3

Safety Profile

Loratadine is well-tolerated with:

• Side effect profile similar to placebo in most studies 4, 5
• No sedation at recommended doses (10mg daily) 1, 4
• No serious ventricular arrhythmias reported (unlike some other second-generation antihistamines) 4
• Occasional mild side effects including headache and fatigue 4

Therapeutic Position

Loratadine is appropriate for:

• First-line treatment of allergic rhinitis 4
• Chronic urticaria 4, 6
• Patients who need to maintain alertness and cognitive function 1

Important Clinical Considerations

• Dosing: Loratadine can be used at higher than recommended doses without sedation, unlike desloratadine which may cause sedation at higher doses 1
• Combination therapy: For patients with inadequate symptom control, loratadine may be combined with intranasal corticosteroids for better efficacy 1, 7
• Treatment approach: Continuous use is more effective than as-needed use for persistent allergic rhinitis 1

Common Pitfalls to Avoid

• Expecting significant relief of nasal congestion with loratadine alone; it's less effective for this symptom 1
• Using loratadine as monotherapy for severe allergic rhinitis; intranasal corticosteroids are more effective 1
• Assuming all second-generation antihistamines have identical sedation profiles; cetirizine and intranasal azelastine may cause sedation at recommended doses, while loratadine does not 1

Loratadine represents an excellent choice for allergic rhinitis treatment when a non-sedating antihistamine is required, offering once-daily dosing convenience with minimal side effects.