Fexofenadine

• Seasonal allergic rhinitis (hay fever)
• Chronic idiopathic urticaria (chronic hives)
• Allergic symptoms relief without sedation
• Long-term allergy management

Fexofenadine is a second-generation antihistamine used for the relief of symptoms associated with allergic rhinitis and chronic idiopathic urticaria. As a selective histamine H1-receptor antagonist with minimal sedating properties and no anticholinergic effects, it provides effective allergy relief without the drowsiness associated with first-generation antihistamines.

Mechanism of Action

Fexofenadine is the active carboxylic acid metabolite of terfenadine, developed after terfenadine was withdrawn due to cardiac toxicity concerns. It selectively blocks histamine H1 receptors on effector cells in the respiratory tract, blood vessels, and gastrointestinal tract, preventing histamine from causing the symptoms of allergic reactions including sneezing, rhinorrhea, itching, and urticaria.

Importantly, fexofenadine does not significantly cross the blood-brain barrier at therapeutic doses, which accounts for its non-sedating properties. It also lacks significant affinity for muscarinic, adrenergic, and other receptor types, avoiding the anticholinergic side effects common with first-generation antihistamines.

Available Formulations

Fexofenadine (Allegra) is available in multiple formulations. Oral tablets come in 30 mg, 60 mg, and 180 mg strengths. An oral suspension (30 mg/5 mL) is available for pediatric use. Orally disintegrating tablets are available for patients who prefer not to swallow tablets. Many formulations are available over-the-counter, while some remain prescription-only depending on the specific product and indication.

FDA-Approved Indications

Fexofenadine is FDA-approved for the relief of symptoms associated with seasonal allergic rhinitis in adults and children 2 years of age and older, treatment of uncomplicated skin manifestations of chronic idiopathic urticaria in adults and children 6 months of age and older, and significantly reduces pruritus and number of wheals in urticaria patients.

Dosing Guidelines

For seasonal allergic rhinitis in adults and children 12 years and older, the recommended dose is 60 mg twice daily or 180 mg once daily. For children 6-11 years, the dose is 30 mg twice daily. For children 2-5 years, use the oral suspension 30 mg twice daily. For chronic idiopathic urticaria in adults and children 12 years and older, 60 mg twice daily or 180 mg once daily is recommended; lower doses are used for children based on age. Doses should be taken with water and should not be taken with fruit juices.

Advantages Over First-Generation Antihistamines

Fexofenadine offers significant advantages over older antihistamines like diphenhydramine and chlorpheniramine. It does not cause significant sedation, allowing patients to maintain normal activities including driving. It lacks anticholinergic effects, avoiding dry mouth, urinary retention, constipation, and blurred vision. There are no cardiac conduction effects (unlike its parent compound terfenadine). These properties make it suitable for long-term use in chronic conditions.

Important Safety Considerations

Fexofenadine is generally well tolerated with a safety profile similar to placebo in clinical trials. Fruit juices (apple, orange, grapefruit) can decrease absorption by approximately 36%, so the medication should be taken with water only. While generally non-sedating, some patients may experience drowsiness. Use with caution in patients with renal impairment, as the medication is primarily excreted renally.

Drug Interactions

Fruit juices significantly reduce fexofenadine absorption and should be avoided when taking the medication. Antacids containing aluminum and magnesium can decrease absorption; separate administration by at least 2 hours. Erythromycin and ketoconazole may increase fexofenadine levels. Unlike some other antihistamines, fexofenadine does not interact with alcohol to enhance sedation.

Special Populations

Dose reduction is recommended in patients with renal impairment: 60 mg once daily is the recommended starting dose in adults with decreased renal function. Fexofenadine is pregnancy category C; use only if benefits outweigh risks. The medication is excreted in breast milk; use caution during breastfeeding. Safety and dosing have been established in children as young as 6 months for urticaria and 2 years for allergic rhinitis.

Learn more at MedlinePlus