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Fexofenadine is the active carboxylic acid metabolite of terfenadine, developed after terfenadine was withdrawn due to cardiac toxicity concerns.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.

Choosing Among the Second-Generation Antihistamines

Fexofenadine, cetirizine, and loratadine are all reasonable first choices for seasonal allergic rhinitis, and the differences between them are practical rather than dramatic. Fexofenadine is the least sedating of the three and is the usual pick for patients who drive commercially, operate machinery, or noticed drowsiness on something else. Cetirizine is generally the most potent for hives (urticaria) and for itch, but a minority of patients find it sedating. Loratadine sits between them and is often the cheapest. Because response is individual, a patient who gets little relief from one is worth switching to another before concluding that antihistamines do not work.

None of them is the strongest treatment for nasal congestion. For moderate or persistent rhinitis, an intranasal corticosteroid such as fluticasone outperforms any oral antihistamine on blockage and is the preferred single agent; the antihistamine is then added for sneezing, itch, and eye symptoms. Montelukast is a second-line option reserved for specific situations because of its neuropsychiatric boxed warning.

Getting the Most Out of It, and When It Is Not Enough

Two administration details decide whether fexofenadine works as well as it should. It is taken with water, not with fruit juice: apple, orange, and grapefruit juice measurably reduce how much drug is absorbed, and a patient who swallows it with breakfast juice every morning may be getting a fraction of the intended dose. Aluminum- and magnesium-containing antacids have the same effect and are separated by a couple of hours. Timing matters too — for predictable seasonal exposure, starting a week or two before the season begins works better than waiting for symptoms, and for hay fever in a climate with a long pollen calendar, continuous dosing through the season beats intermittent use.

If symptoms persist on a correctly taken antihistamine plus an intranasal steroid, the diagnosis is worth revisiting rather than the dose being doubled. Non-allergic rhinitis, chronic sinusitis, a deviated septum, and medication-induced congestion from decongestant sprays all mimic allergy and none of them responds to an H1 blocker. Persistent hives beyond six weeks is a separate problem that is managed with higher antihistamine dosing under supervision and sometimes with biologic therapy. The MedlinePlus fexofenadine monograph covers the administration rules, and the MedlinePlus hay fever topic reviews the broader management of allergic rhinitis. Our immunology team evaluates patients whose symptoms outlast standard treatment, and the local pollen calendar is covered in our article on Florida pollen season and in our guide to chronic hives lasting six weeks.

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. Human data in pregnancy are limited, so fexofenadine is used in pregnancy only when the benefit justifies it; discuss it with your obstetric clinician. 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