Generic Name

Loratadine

Mechanism

• Selective antagonism of peripheral H₁ receptors → blocks histamine‑mediated vasodilation, pruritus, and secretory activities.
• Minimal crossing of the blood–brain barrier → negligible sedation compared to first‑generation agents.
• Activated by hepatic CYP450 (mainly CYP3A4) to its active metabolite, fexofenadine, which contributes to its antihistaminic effect.

Pharmacokinetics

• Absorption: ~70 % oral bioavailability; peak plasma concentration (t_max) ~3–4 h.
• Distribution: Moderate plasma protein binding (~15 %); little CNS distribution.
• Metabolism: Liver CYP3A4 → primarily fexofenadine; minor renal excretion (~30 % unchanged).
• Half‑life: 8–12 h (dose‑dependent).
• Drug interactions: Strong CYP3A4 inhibitors (ketoconazole, itraconazole) ↑ plasma levels; strong inducers (rifampin, carbamazepine) ↓ levels.

Indications

• Allergic rhinitis (seasonal or perennial) – symptomatic relief of sneezing, nasal congestion, & itching.
• Chronic idiopathic urticaria – reduces hives and angioedema.
• Allergic conjunctivitis – alleviates ocular pruritus and tearing.

Contraindications

• Hypersensitivity to loratadine or any excipients.
• Severe hepatic impairment (Child‑Pugh B/C) – dose reduction or avoidance.
• Pregnancy: Category B; safe in pregnancy if benefits outweigh risks.
• Q T‑prolongation: Rare; caution in patients on QT‑prolonging drugs.
• Concurrent use with other antihistamines or sedatives may enhance CNS effects.

Dosing

• Adults: 10 mg PO once daily.
• Pediatrics (≥6 yrs): 5–10 mg PO once daily (dose = 0.6 mg/kg max 5 mg).
• Children (2–6 yrs): 5 mg PO once daily.
• Infants (<2 yrs): Not recommended.
• Administration: With or without food; avoid excessive alcohol.

Adverse Effects

Monitoring

• Hepatic function tests (AST, ALT, bilirubin) in patients with liver disease or on interacting drugs.
• QTc interval if on concomitant QT‑prolonging agents.
• Renal function may be monitored for high‑dose or prolonged therapy; not routinely required.
• Symptom control (nasal congestion score, wheals) to assess therapeutic response.

Clinical Pearls

• First‑line for non‑sedating antihistamine therapy: Loratadine is favored when sleep disturbance must be minimized.
• Pediatric dosing: Start at 5 mg; increase to 10 mg if tolerated and benefit‑needs support.
• Drug interactions: Strong CYP3A4 inhibitors (ketoconazole, itraconazole) can raise loratadine levels by ~50‑70 %; consider therapeutic drug monitoring or dose adjustment.
• Rapid onset: For breakthrough symptoms, a 10 mg dose can be taken at any time—its long half‑life maintains coverage.
• Oral vs. transdermal: No transdermal formulation exists, but loop‑to‑relate isn’t required compared to intranasal steroids.
• Cost‑effectiveness: Generic loratadine is inexpensive, often covered by insurance, making it a first‑choice for chronic urticaria.
• Combination therapy: Often paired with intranasal corticosteroids for severe seasonal allergic rhinitis; synergistic and reduces overall steroid need.

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• *Key pharmacology terms: H1 receptor antagonist, second‑generation antihistamine, CYP3A4 metabolism, fexofenadine, non‑sedating.*

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