Fexofenadine

Usage

• Fexofenadine is prescribed for the relief of symptoms associated with seasonal allergic rhinitis (hay fever) and chronic idiopathic urticaria (hives).
• Pharmacological Classification: Second-generation non-sedating antihistamine.
• Mechanism of Action: Selectively antagonizes peripheral histamine H1-receptors, thereby reducing the effects of histamine release in allergic reactions.

Alternate Names

• Fexofenadine hydrochloride.
• Brand Names: Allegra, Telfast, and various generic formulations.

How It Works

• Pharmacodynamics: Fexofenadine competitively binds to peripheral H1 receptors, inhibiting histamine-mediated responses such as vasodilation, bronchoconstriction, and increased capillary permeability. It reduces symptoms like sneezing, itching, rhinorrhea, and urticaria. It exhibits minimal penetration into the central nervous system, leading to a lower incidence of sedation compared to first-generation antihistamines.

• Pharmacokinetics:

  • Absorption: Well absorbed orally, with peak plasma concentrations reached in approximately 1-3 hours. Food may slightly decrease the rate of absorption, especially for the 120mg and 180mg tablets, but not the extent.
  • Metabolism: Minimally metabolized in the liver (about 5%).
  • Elimination: Primarily excreted unchanged in feces (approximately 80%) and urine (approximately 11%), with a half-life of 11-15 hours.

• Mode of Action: Competitive antagonism of peripheral H1-receptors.

• Receptor Binding: Selective for peripheral H1-receptors, minimal affinity for other receptor types.

• Elimination Pathways: Primarily fecal excretion, some renal excretion.

Dosage

Standard Dosage

Adults:

• Seasonal Allergic Rhinitis: 120mg once daily OR 60mg twice daily.
• Chronic Idiopathic Urticaria: 180mg once daily OR 60 mg twice daily.
• Administer with water. For 120mg and 180mg tablets, administration before meals is recommended. 30mg tablets can be taken with or without food.

Children:

• 6 months to <2 years: 15mg twice daily (for chronic idiopathic urticaria only).
• 2-11 years: 30mg twice daily (for both indications).
• 12 years and older: Follow adult dosing.

Special Cases:

• Elderly Patients: Initiate with a lower dose (60mg once daily) and adjust as needed based on renal function.
• Patients with Renal Impairment: Initial dose of 60mg once daily, with further adjustments based on the degree of impairment.
• Patients with Hepatic Dysfunction: No specific dosage adjustment is usually necessary.
• Patients with Comorbid Conditions: Exercise caution in patients with heart disease or long QT syndrome, and consider potential drug interactions.

Clinical Use Cases

Fexofenadine’s clinical use is primarily limited to the treatment of allergic rhinitis and urticaria. The dosages mentioned in the standard dosage section apply across various clinical settings. Fexofenadine is not indicated for intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations.

Dosage Adjustments

• Renal impairment necessitates dosage reductions. See special cases section.
• Drug interactions with erythromycin, ketoconazole, aluminum/magnesium-containing antacids, and fruit juices (especially grapefruit, apple, and orange juice) may necessitate dosage adjustments or other precautions.

Side Effects

Common Side Effects:

Headache, back pain, dizziness, nausea, vomiting, diarrhea, fatigue, drowsiness, dysmenorrhea, cough, upper respiratory tract infection, fever, and ear infection.

Rare but Serious Side Effects:

Allergic reactions (including anaphylaxis, angioedema), rash, urticaria, pruritus, chest tightness, and dyspnea.

Long-Term Effects:

Limited data exist on the long-term effects of Fexofenadine. Monitor for any new or worsening symptoms with prolonged use.

Adverse Drug Reactions (ADR):

Severe allergic reactions requiring immediate medical attention.

Contraindications

• Hypersensitivity to Fexofenadine or any components of its formulation.

Drug Interactions

• Antacids: Aluminum and magnesium-containing antacids reduce Fexofenadine absorption. Administer at least 2 hours apart.
• CYP3A4 Inhibitors (e.g., Ketoconazole, Erythromycin): May increase Fexofenadine plasma concentrations. Monitor for adverse effects and consider dosage adjustments.
• Fruit Juices: Grapefruit, apple, and orange juices may reduce Fexofenadine absorption. Avoid concomitant administration.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: C (consult specialist before prescribing during pregnancy; weigh benefits against potential risks).
• Fetal Risks: Limited human data. Animal studies have shown no adverse fetal effects. Use only if clearly needed.
• Breastfeeding: Fexofenadine is excreted in breast milk. Exercise caution and consider the potential for infant effects.

Drug Profile Summary

• Mechanism of Action: Peripheral H1-receptor antagonist.
• Side Effects: Headache, dizziness, nausea, fatigue, upper respiratory tract infection. Rarely, severe allergic reactions.
• Contraindications: Hypersensitivity.
• Drug Interactions: Antacids, CYP3A4 inhibitors (ketoconazole, erythromycin), fruit juices.
• Pregnancy & Breastfeeding: Category C; excreted in breast milk; use with caution.
• Dosage: Adults: 120mg/180mg once daily or 60mg twice daily. Children: See pediatric dosing.
• Monitoring Parameters: Observe for allergic reactions and adverse events. Periodically assess symptom control and renal function, especially in elderly and renally impaired patients.

Popular Combinations

Fexofenadine is sometimes combined with pseudoephedrine (a decongestant) for treating allergic rhinitis with nasal congestion. Brand examples include Allegra-D.

Precautions

• General Precautions: Assess for allergies, renal/hepatic function, and concomitant medications.
• Specific Populations: See dosage section for pregnancy, breastfeeding, children, and elderly patients.
• Lifestyle Considerations: Alcohol may potentiate drowsiness. Advise patients to avoid driving or operating machinery until their individual response to Fexofenadine is determined.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Fexofenadine?

A: Adults: 120mg once daily for hay fever or 180mg once daily for hives; alternatively, 60mg twice daily for either condition. Children: see detailed pediatric dosing in the dosage section.

Q2: Can Fexofenadine be taken with food?

A: 30mg tablets can be taken with or without food. 120mg and 180mg tablets are preferably taken before meals.

Q3: How does Fexofenadine differ from first-generation antihistamines?

A: Fexofenadine is less sedating due to its reduced penetration into the central nervous system.

Q4: Can pregnant or breastfeeding women take Fexofenadine?

A: Consult a specialist. Category C drug; use only if clearly needed. Excreted in breast milk.

Q5: What should I do if a patient misses a dose?

A: Take the missed dose as soon as remembered, unless it is close to the next scheduled dose. Do not double the dose.

Q6: What are the signs of a Fexofenadine overdose?

A: Dizziness, drowsiness, fatigue, and dry mouth. Seek immediate medical attention if an overdose is suspected.

Q7: Are there any specific monitoring parameters for Fexofenadine?

A: Monitor for allergic reactions and other adverse effects. Evaluate symptom control. Periodically assess renal function in elderly patients and those with renal impairment.

Q8: What are the most common drug interactions with Fexofenadine?

A: Antacids, CYP3A4 inhibitors (e.g., ketoconazole, erythromycin), and fruit juices (grapefruit, apple, and orange) can affect Fexofenadine absorption or metabolism.

Q9: Can Fexofenadine be used to treat acute urticaria?

A: Yes, Fexofenadine is effective for both chronic and acute urticaria.