Introduction
Loratadine is a second-generation, long-acting antihistamine with selective peripheral H₁-receptor antagonist activity. It is widely used for the symptomatic relief of allergic conditions due to its efficacy and favorable side effect profile compared to first-generation antihistamines. First approved by the FDA in 1993, loratadine has become one of the most commonly prescribed antihistamines worldwide.
Mechanism of Action
Loratadine competitively inhibits histamine release at H₁-receptor sites, preventing histamine-mediated allergic responses. Unlike first-generation antihistamines, loratadine has minimal affinity for central nervous system receptors due to its limited ability to cross the blood-brain barrier. This results in effective peripheral antihistaminic effects with significantly reduced sedative properties.
Indications
- Seasonal allergic rhinitis
- Perennial allergic rhinitis
- Chronic idiopathic urticaria
- Allergic conjunctivitis (off-label)
- Other allergic skin conditions (off-label)
Dosage and Administration
Adults and children ≥6 years: 10 mg orally once daily Children 2-5 years: 5 mg orally once daily Renal impairment (CrCl <30 mL/min): Initial dose 10 mg every other day Hepatic impairment: Initial dose 10 mg every other day Administration: May be taken with or without foodPharmacokinetics
Absorption: Rapidly absorbed from GI tract; Tmax = 1-2 hours Distribution: Volume of distribution = 119 L; 97-99% protein bound Metabolism: Extensive first-pass metabolism via CYP3A4 and CYP2D6 to active metabolite descarboethoxyloratadine Elimination: Half-life = 8.4 hours (parent drug), 28 hours (active metabolite); primarily excreted in urine (40%) and feces (40%)Contraindications
- Hypersensitivity to loratadine or any component of the formulation
- Patients with known hypersensitivity to similar chemical compounds (azatadine, cyproheptadine)
Warnings and Precautions
- Use with caution in patients with hepatic impairment
- Elderly patients may be more susceptible to adverse effects
- Not recommended for children under 2 years
- Pregnancy Category B: Use only if clearly needed
- Excreted in breast milk; caution advised in nursing mothers
Drug Interactions
Strong CYP3A4 inhibitors: Ketoconazole, erythromycin, cimetidine - may increase loratadine levels CNS depressants: Additive effects possible, though less likely than with first-generation antihistamines Alcohol: Minimal interaction, but caution advisedAdverse Effects
Common (≥1%):- Headache (12%)
- Somnolence (8%)
- Fatigue (4%)
- Dry mouth (3%)
- Tachycardia
- Palpitations
- Hypersensitivity reactions
- Hepatitis (rare)
- Seizures (rare)
Monitoring Parameters
- Symptom relief and therapeutic response
- Adverse effects, particularly CNS effects in elderly patients
- Liver function tests in patients with hepatic impairment
- Renal function in patients with pre-existing renal disease
Patient Education
- Take medication as directed, typically once daily
- May take with or without food
- Report any persistent drowsiness, palpitations, or unusual symptoms
- Avoid alcohol while taking medication
- Notify healthcare provider if pregnant, planning pregnancy, or breastfeeding
- Store at room temperature away from moisture and heat
References
1. FDA Prescribing Information: Claritin (loratadine) 2. Simons FER. Advances in H₁-antihistamines. N Engl J Med. 2004;351(21):2203-2217 3. Meltzer EO. The role of nasal corticosteroids in the treatment of rhinitis. Immunol Allergy Clin North Am. 2011;31(3):545-560 4. Zuberbier T, et al. EAACI/GA²LEN/EDF guideline: management of urticaria. Allergy. 2018;73(7):1393-1414 5. Church MK, Maurer M. H₁-antihistamines and urticaria: how can we predict the best drug for our patient? Clin Exp Allergy. 2012;42(10):1423-1429