What is Loratadine?
Loratadine is a second-generation oral antihistamine (H1-receptor antagonist) used primarily for treating allergic rhinitis and chronic urticaria, with the key advantage of being non-sedating at recommended doses. 1
Drug Classification and Mechanism
- Loratadine is a long-acting antihistamine with high selectivity for peripheral histamine H1-receptors, exhibiting minimal central nervous system penetration 2, 3
- It has a threefold greater affinity for peripheral versus central H1-receptors, which accounts for its non-sedating profile 4
- The drug has one main active metabolite, descarboethoxyloratadine (desloratadine), which is four times more active than the parent compound 4
Pharmacokinetics
- Onset of action: Within 1 hour 4, 5
- Peak plasma concentration: 1-2 hours for loratadine; 3-4 hours for the active metabolite 4
- Elimination half-life: Approximately 10 hours for loratadine and 20 hours for its metabolite 4
- Duration of action: At least 24 hours, allowing once-daily dosing 4, 6
Approved Indications
Allergic Rhinitis (Seasonal and Perennial)
- Effective for reducing rhinorrhea, sneezing, nasal itching, and associated ocular symptoms 1
- Less effective for nasal congestion compared to other nasal symptoms 1
- Continuous use is more effective than intermittent use for seasonal or perennial allergic rhinitis, though appropriate for as-needed use in episodic allergic rhinitis 1
Chronic Urticaria
- Demonstrated efficacy comparable to other second-generation antihistamines 2, 3
- Well-tolerated with minimal adverse effects 7
Dosing
Standard Dosing (FDA-Approved) 8
- Adults and children ≥6 years: 10 mg (2 teaspoonfuls of 5 mg/5 mL solution) once daily
- Children 2 to <6 years: 5 mg (1 teaspoonful) once daily
- Children <2 years: Consult physician
- Patients with liver or kidney disease: Consult physician 8
Important Dosing Considerations
- Do not exceed recommended daily dose within 24 hours 8
- Patients with low body mass may reach elevated dosage levels (mg/kg basis) and potentially develop drowsiness or performance impairment even at standard doses 1
Side Effects and Safety Profile
Sedation Profile
- At recommended doses: Loratadine does NOT cause sedation compared to placebo 1
- Above recommended doses: May cause sedation 1
- Sedation incidence in clinical trials: approximately 3-10%, comparable to placebo 6, 5
Common Adverse Effects
- Headache, fatigue, and somnolence are most commonly reported, though incidence is similar to placebo 2
- Dry mouth: approximately 4% incidence 6
- Overall adverse event incidence: 14% 6
Comparative Safety
- Significantly less sedation than first-generation antihistamines (azatadine, cetirizine, chlorpheniramine, clemastine, mequitazine) 2, 3
- No serious ventricular arrhythmias reported, unlike some other second-generation antihistamines 2
- No anticholinergic effects compared to first-generation antihistamines 1
Special Populations
Renal Impairment
- Use with caution in severe renal impairment (creatinine clearance <10 mL/min) 7
Hepatic Impairment
- Consult physician before use 8
Pregnancy and Lactation
- U.S. FDA Pregnancy Category B (no evidence of harm, but well-controlled human studies lacking) 7
- Avoidance or caution recommended, particularly in first trimester 7
Pediatric Use
- Well-tolerated with good safety profile in children when used at appropriate doses 1
- Not contraindicated in children ≥12 years 7
Clinical Positioning
Preferred Status
- Second-generation antihistamines like loratadine are generally preferred over first-generation antihistamines for allergic rhinitis treatment due to lack of sedation, performance impairment, and anticholinergic effects at recommended doses 1
Comparative Efficacy
- No single second-generation antihistamine has been conclusively found superior to others in overall response rates 1
- Comparable efficacy to terfenadine, cetirizine, and other second-generation agents 2, 6, 5
- Faster acting than astemizole 2, 3
Limitations
- Less effective than intranasal corticosteroids for allergic rhinitis 1
- Generally ineffective for nonallergic rhinitis 1
- Limited objective effect on nasal congestion 1
Key Clinical Pearls
- Loratadine should be discontinued 3-4 days before skin prick testing (based on its elimination half-life) 7
- Performance impairment can occur in patients with low body mass even at standard doses due to elevated mg/kg dosing 1
- Once-daily dosing improves compliance compared to twice-daily alternatives 4
- Appropriate as first-line monotherapy for mild-to-moderate allergic rhinitis and chronic urticaria 2, 3