Adults

For seasonal allergic rhinitis: 48 mg once or twice daily, as directed by a physician. For chronic idiopathic urticaria: 48 mg once or twice daily, as directed by a physician. (Standard Fexofenadine doses are typically 60mg BID or 120/180mg OD)

Elderly

No specific dose adjustment is generally required, but caution should be exercised in elderly patients with renal impairment.

Renal_impairment

For patients with impaired renal function (creatinine clearance <80 mL/min), a lower initial dose should be considered (e.g., 60 mg once daily for standard doses, adjust accordingly for 48mg if severe impairment).

Onset

Onset of action is approximately 1 hour.

Excretion

Primarily excreted unchanged in feces (approximately 80%) and urine (approximately 10%).

Half life

The elimination half-life is approximately 11-15 hours.

Absorption

Rapidly absorbed after oral administration; peak plasma concentrations (Tmax) are typically achieved within 1-3 hours. Bioavailability can be affected by food and certain fruit juices.

Metabolism

Minimally metabolized; approximately 5% of the total dose is metabolized by the liver, indicating a low potential for drug interactions via hepatic enzymes.

Erythromycin and Ketoconazole

Co-administration with erythromycin or ketoconazole has been shown to slightly increase plasma concentrations of fexofenadine, but this is generally not considered clinically significant.

Antacids (aluminum and magnesium-containing)

Concomitant administration of antacids containing aluminum or magnesium hydroxide can reduce the absorption of fexofenadine. Separate administration by at least 2 hours.