Fexofenadine

Absorption

Fexofenadine is rapidly absorbed following oral administration and its absolute bioavailability is approximately 33%. The Tmax following oral administration is approximately 1-3 hours. The steady-state AUCss(0-12h) and Cmax following twice daily dosing of 60mg are 1367 ng/mL.h and 299 ng/mL, respectively.
Fexofenadine AUC is decreased by >20% when coadministered with fruit juices (e.g. apple, orange, grapefruit) due to their inhibition of OATP transporters - for this reason, prescribing information recommends administering fexofenadine only with water. Similarly, coadministration of fexofenadine with a high-fat meal appears to decrease AUC and Cmax by >20%.

Toxicity

No deaths were observed following the oral administration of up to 5000 mg/kg in both mice and rats (equivalent to approximately 100-200x the recommended human dose). Single doses of up to 800 mg and chronic exposure of up to 690 mg twice daily for 1 month in humans did not result in clinically significant adverse events. Symptoms of overdosage are consistent with fexofenadine's adverse effect profile and are likely to include dizziness, drowsiness, and dry mouth.
If overdosage occurs, employ symptomatic and supportive treatment. Hemodialysis does not effectively remove fexofenadine from the blood and is therefore of no benefit.

Description

Fexofenadine, the carboxylic acid metabolite of terfenadine, is widely available. It accounts for the antihistaminic properties of terfenadine, which is very rapidly metabolized via CYP3A4-catalyzed processes. Members of the organic anion transporter protein family and the drug efflux transporter P-glycoprotein are involved in the disposition of fexofenadine. Fexofenadine does not have the antiarrhythmic side effects of terfenadine.

The Uses of Fexofenadine

A metabolite of of terfenadine, a H1-Histamine receptor antagonist

Background

Fexofenadine is an over-the-counter second-generation antihistamine used in the treatment of various allergic symptoms. It is selective for the H1 receptor, carries little-to-no activity at off-targets, and does not cross the blood-brain barrier - this is in contrast to previous first-generation antihistamines, such as diphenhydramine, which readily bind to off-targets that contribute to side effects such as sedation. Fexofenadine is the major active metabolite of terfenadine and is administered as a racemic mixture in which both enantiomers display approximately equivalent antihistamine activity.

What are the applications of Application

Fexofenadine is A metabolite of of terfenadine, a H1-Histamine receptor antagonist

Indications

In the United States, fexofenadine is indicated for the symptomatic treatment of allergic rhinitis in patients ≥2 years old and chronic idiopathic urticaria in patients ≥6 months old. In Canada, fexofenadine carries the same indications but is approved only for patients ≥12 years old. Fexofenadine is also available in combination with pseudoephedrine for the symptomatic treatment of season allergic rhinitis in patients ≥12 years old.

Pharmacokinetics

Fexofenadine relieves allergy symptoms by antagonizing the actions of histamine, an endogenous compound predominantly responsible for allergic symptomatology. The relatively long duration of action of fexofenadine (approximately 24 hours) allows for once or twice daily dosing, and its rapid absorption allows for an onset of action within 1-3 hours. Fexofenadine should not be taken with fruit juice, as this may impair its absorption.

Metabolism

Fexofenadine is very minimally metabolized, with only 5% of an ingested dose undergoing hepatic metabolism. The only identified metabolites are a methyl ester of fexofenadine (3.6% of the total dose) and MDL 4829 (1.5% of the total dose). The enzymes responsible for this metabolism have not been elucidated.