Fexofenadine

Fexofenadine (fex-oh-fin’a-deen) is a second generation H1-antagonist for the treatment of allergic rhinitis and idiopathic urticaria that is generally available over-the-counter. It is listed on the World Health Organization’s List of Essential Medicines.

Mechanism of action:
Fexofenadine is a selective peripheral H1 receptor antagonist preventing the activation of the H1 receptors by histamine. It has a relatively longer duration of action of about 24 hours which will allow for for once or twice daily dosing. Absorption is rapid with an onset of action within 1 to 3 hours.
Fexofenadine does not easily cross the blood–brain barrier to act centrally, causing less drowsiness in comparison to the first generation H1 antagonists.

Pharmacokinetics:
Bioavailability is 30–41% with 60-70% protein binding (mostly albumin).
Elimination half-life is 11-15 hours.
Excretion is mostly via the faeces and urine (~10%) as an unchanged drug due to low metabolism (only 5% of an ingested dose undergoes hepatic metabolism).

Brand names: Allegra, Telfast, Almerg, Treathay and many others
Chemical formula: C₃₂H₃₉NO₄

Dosage:
Generally, for adults and children aged over 12: 60mg two times a day, or 180 mg once a day.

Contraindications:
Hypersensitivity; breast feeding; young children

Cautions:
Pregnancy category C; closed angle glaucoma

Interactions:
Include: using erythromycin or ketoconazole while also taking fexofenadine does increase the plasma levels of fexofenadine.
Apple, orange or grapefruit juice could decrease absorption of Fexofenadine.

Side effects:
Most common: Vomiting; headache
Less common: Body and muscle aches; dizziness; drowsiness; menstrual cramps

In Australia, Fexofenadine is on the National Podiatry Scheduled Medicines List for use by authorised Podiatrists.

Examples of other H1 Antagonists (Anti-histamines):

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