Introduction
Claritin (loratadine) is a second-generation antihistamine medication widely used for the management of allergic conditions. As a selective peripheral H1-receptor antagonist, it provides effective relief from allergy symptoms with minimal sedative effects compared to first-generation antihistamines. First approved by the FDA in 1993, loratadine has become one of the most commonly prescribed and over-the-counter antihistamines worldwide.
Mechanism of Action
Loratadine competitively inhibits histamine H1 receptors in the gastrointestinal tract, blood vessels, and respiratory tract. Unlike first-generation antihistamines, loratadine demonstrates minimal penetration of the blood-brain barrier due to its zwitterionic properties at physiological pH, resulting in significantly reduced central nervous system effects. The drug prevents histamine-mediated inflammatory responses, including vasodilation, increased vascular permeability, and smooth muscle contraction.
Indications
- Seasonal allergic rhinitis (hay fever)
- Perennial allergic rhinitis
- Chronic idiopathic urticaria (hives)
- Allergic conjunctivitis (when administered as eye drops)
- Relief of itching and redness associated with allergic skin conditions
Dosage and Administration
Adults and children ≥6 years: 10 mg once daily Children 2-5 years: 5 mg once daily Patients with hepatic impairment: Initial dose of 10 mg every other day Renal impairment (CrCl <30 mL/min): Initial dose of 10 mg every other dayAvailable formulations include tablets, rapidly-disintegrating tablets, syrup, and combination products with pseudoephedrine. Administration with food may increase bioavailability but is not required for efficacy.
Pharmacokinetics
Absorption: Rapidly absorbed from GI tract; Tmax = 1-2 hours; bioavailability approximately 40% due to first-pass metabolism Distribution: Volume of distribution = 119 L; 97% protein-bound; minimal CNS penetration Metabolism: Extensive hepatic metabolism via CYP3A4 and CYP2D6 to active metabolite descarboethoxyloratadine Elimination: Biphasic elimination; terminal half-life = 8.4 hours (parent drug) and 28 hours (active metabolite); excreted equally in urine and fecesContraindications
- Hypersensitivity to loratadine or any component of the formulation
- Concurrent use with certain antifungal agents (ketoconazole, itraconazole) or macrolide antibiotics (erythromycin, clarithromycin) in patients with hepatic impairment
Warnings and Precautions
- Use with caution in patients with hepatic impairment (dose adjustment required)
- Elderly patients may be more sensitive to adverse effects
- Not recommended for children under 2 years due to limited safety data
- May cause drowsiness in susceptible individuals (approximately 2% of patients)
- Use during pregnancy only if clearly needed (Pregnancy Category B)
- Excreted in breast milk; use with caution in nursing mothers
Drug Interactions
Strong CYP3A4/CYP2D6 inhibitors: Ketoconazole, erythromycin, cimetidine - may increase loratadine levels CNS depressants: Alcohol, benzodiazepines, opioids - potential additive sedative effects P-glycoprotein substrates: Possible increased concentrations of co-administered P-gp substrates Anticholinergic agents: Potential additive anticholinergic effectsAdverse Effects
Common (≥1%):- Headache (12%)
- Somnolence (8%)
- Fatigue (4%)
- Dry mouth (3%)
- Gastrointestinal disturbances (nausea, diarrhea)
- Tachycardia
- Hypersensitivity reactions (anaphylaxis, angioedema)
- Hepatotoxicity (rare)
- Seizures (rare case reports)
Monitoring Parameters
- Allergy symptom control and relief
- Signs of excessive sedation or CNS effects
- Hepatic function in patients with pre-existing liver disease
- Heart rate in patients with cardiac conditions
- Adverse effects requiring dose adjustment
Patient Education
- Take as directed, typically once daily with or without food
- Report any excessive drowsiness, palpitations, or unusual symptoms
- Avoid alcohol and other sedating medications
- Notify healthcare provider if pregnant, planning pregnancy, or breastfeeding
- Store at room temperature away from moisture
- Seek immediate medical attention for signs of allergic reaction (difficulty breathing, swelling)
- Do not crush or chew rapidly-disintegrating tablets; allow to dissolve on tongue
References
1. Simons FER. Advances in H1-antihistamines. N Engl J Med. 2004;351(21):2203-2217. 2. FDA prescribing information: Claritin (loratadine). Revised 2022. 3. Meltzer EO. The prevalence and medical and economic impact of allergic rhinitis in the United States. J Allergy Clin Immunol. 1997;99(6):S805-S828. 4. Bachert C. A review of the efficacy of desloratadine, fexofenadine, and loratadine in the treatment of nasal congestion in patients with allergic rhinitis. Clin Ther. 2009;31(5):921-944. 5. UpToDate. Loratadine: Drug information. Accessed January 2024. 6. Zuberbier T, et al. EAACI/GA²LEN/EDF/WAO guideline: management of urticaria. Allergy. 2018;73(7):1393-1414. 7. Church MK, Maurer M. H1-antihistamines and urticaria: how can we predict the best drug? Br J Dermatol. 2012;166(5):954-958.