Fexofenadine

Fexofenadine is an antihistamine drug approved by the USFDA in 1996 and used to treat seasonal infections like allergic rhinitis, runny nose, watery eyes, and chronic urticaria. It can be used in the treatment of both adults and children. It is a second-generation antihistamine that exhibits reduced affinity for cholinergic and α-adrenergic receptors, which helps in minimal anticholinergic effects. Fexofenadine was found to be effective in ocular and nasal congestion symptoms. It is also effective in treating cholinergic urticaria. Chronic urticarial causes are mainly due to mast cell degranulation. Fexofenadine is considered safe and effective for allergic rhinitis and urticaria.

BRAND NAMES:

Allegra – Allegra contains a composition of Fexofenadine hydrochloride tablets of 120 mg, which is used in treating seasonal allergic symptoms.

Allegra ODT – It is an orally disintegrating tablet available in the form of Allegra ODT fexofenadine hydrochloride 30 mg tablets.

MECHANISM OF ACTION:

Compared to first-generation antihistamines, fexofenadine reduces the blood-brain barrier and does not cause drowsiness. It lowers affinity for cholinergic and α-adrenergic receptors, leading to minor anticholinergic effects. Histamine works by attaching to histamine receptors on the surfaces of different cells. The H1 receptor is principally important for mediating allergic reactions. By binding to H1 receptors, it effectively prevents histamine from binding to them. This stops histamine from acting on target cells, lowering the symptoms of allergic reactions.

PHARMACOKINETICS:

Absorption: Suspensions attain maximal plasma concentration 1 hour after administration, while tablets require 1.5 hours. 

Distribution: Fexofenadine has a plasma protein binding rate of 60 to 70%. Fexofenadine does not bind to receptors in the central nervous system. 

Metabolism: An estimated 5% of the oral dosage is metabolized. 

Excretion: Faeces will remove about 80%, and urine will eliminate 11%. The bioavailability of fexofenadine hydrochloride has not been assessed; it is uncertain if the fecal component is the product of biliary excretion or an unabsorbed medication.

PHARMACODYNAMICS:

Fexofenadine improves allergy symptoms by inhibiting the effects of histamine, an endogenous molecule primarily responsible for allergic reactions. Fexofenadine's lengthy duration of action allows for once or twice a day administration, and its fast absorption results in a beginning of action within 1-3 hours.

DOSE AND ADMINISTRATION:

Fexofenadine tablets are available in three forms: orally dissolving, suspensions, and tablets. Disintegrating pills should be taken with an empty stomach. 

Allergic Rhinitis: Adults and children over 12 should take 60 mg twice daily, and 180 mg once daily. Patients with reduced renal function should begin with a 60-mg dosage. It is recommended that children aged 6 to 11 years take 30 mg twice daily. Children with impaired renal function should begin with 30 mg once daily. 

Chronic idiopathic urticaria: A dose of 60 mg twice daily is advised for adults and children over the age of twelve. With impaired renal function, a beginning dose of 60 mg is indicated. It is recommended that children aged 6 to 11 years take 30 mg twice daily. A starting dose of 30 mg daily is indicated for pediatric patients with impaired renal function. 

If the dosing schedule is missed, do not take multiple pills at once. Take according to your next regular dose.

CONTRAINDICATIONS:

Patients with renal disease must take possible precautions—hypersensitivity to fexofenadine or related to its components.

DRUG INTERACTIONS:

The combination of fexofenadine, ketoconazole, and erythromycin elevated plasma levels of fexofenadine. It makes no difference to the pharmacokinetics of ketoconazole or erythromycin. Under steady-state circumstances, healthy volunteers responded appropriately when given fexofenadine 120 mg twice a day along with 500 mg of erythromycin every 8 hours and 400 mg once a day. When patients took fexofenadine hydrochloride alone or in combination with erythromycin or ketoconazole, neither the adverse effects nor the QTc interval changed.

It should not be used with aluminum or magnesium-containing antacids.

FOOD INTERACTIONS:

While taking fexofenadine, avoid eating fruits or drinking fruit juices such as oranges, apples, and grapes.

ADVERSE EFFECTS:

•    Headache

•    Upper respiratory tract infection

•    Back pain

•    Fatigue

•    Flu and cold symptoms like sinus, fever, ear pain, and stuffy nose.

•    Cough

•    Fatigue

TOXICITY:

Single doses of fexofenadine up to 800 mg, 690 mg twice a day for one month, or 240 mg once daily for one year were delivered without producing clinically significant side effects compared to a placebo. Symptomatic and supportive care is advised. Hemodialysis did not adequately eliminate fexofenadine from the blood. Fexofenadine oral doses did not result in any deaths. It is a terfenadine metabolite known to have cardiotoxic effects. When taken in high quantities with some medications, such as ketoconazole, it inhibits cardiac potassium channels, resulting in prolonged QT intervals.

STORAGE CONDITIONS:

Store at room temperature. Keep away from moisture, heat, and direct light.