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Fexofenadine (Allegra) - Uses, Dosage, Side Effects, Drug Warnings, and Precautions

Published on Feb 24, 2022 and last reviewed on Aug 22, 2022   -  7 min read


Fexofenadine is a drug used to relieve symptoms of allergies such as runny nose, watery eyes, body itching, itchy eyes, sneezing, hives, etc. Learn about its uses, dosage, drug warnings, side effects, precautions, drug interactions, and more.

Fexofenadine (Allegra) - Uses, Dosage, Side Effects, Drug Warnings, and Precautions


Fexofenadine is the active form of Terfenadine, which is the first non-sedating second-generation antihistamine (H1 receptor blocker). Terfenadine was withdrawn because of several deaths due to polymorphic ventricular tachycardia occurring with its higher doses or when it was coadministered with CYP3A4 inhibitors (Erythromycin, Clarithromycin, Ketoconazole, Itraconazole, etc.). This toxicity is based on the blockage of delayed rectifier K+ channels in the heart at higher concentrations.

But Fexofenadine blocks potassium channels comparatively lower than Terfenadine so, it does not prolong QTc interval, but it is not entirely safe in patients with long QT, bradycardia, or hypokalemia. On the other hand, Fexofenadine is widely helpful in allergic rhinitis, urticaria, eczema, and other allergic reactions, etc.


This tablet contains,

  1. Active Ingredient:Fexofenadine.

  2. Inactive Ingredient:

  • Powdered cellulose.

  • Mannitol.

  • Maize starch.

  • Croscarmellose sodium.

  • Magnesium stearate.

  • Colloidal anhydrous silica.

Drug Group:

Fexofenadine (Allegra) belongs to the class of drugs called antihistamines. Antihistamines are drugs that block the actions of histamine, which causes allergic reactions to the body. Thus, Fexofenadine helps to relieve symptoms of allergies, sneezing, lacrimation, rhinorrhea, itchy and red eyes, etc.

What Is Fexofenadine Used For?

The uses of Fexofenadine are as follows,

1. Allergic rhinitis - It is used in allergic rhinitis and helps to relieve the symptoms associated with seasonal and perennial allergic rhinitis in adults and children above 12 years of age. It effectively treats its associated symptoms such as,

  • Sneezing.

  • Rhinorrhea.

  • Lacrimation.

  • Itchy and red eyes.

  • Itchy nose or palate or throat.

2. Cures conjunctivitis.

3. Helps to relieve symptoms of hay fever.

4. Used in pollinosis.

5. Fights with urticaria (also called hives) - Helps to reduce the signs and symptoms of chronic idiopathic urticaria, the number of wheals, and pruritus.

6. Useful in dermographism.

7. Atopic eczema.

8. Works for acute allergic reactions to drugs and foods.

9. Fexofenadine is also available in combination with pseudoephedrine for the symptomatic treatment of seasonal rhinitis in patients above 12 years of age.

Advantage of Fexofenadine:

  1. Absence of central nervous system depressant property.

  2. It does not produce subjective effects.

  3. It does not potentiate alcohol or benzodiazepines.

  4. It does not induce sleep.

  5. It does not impair psychomotor performance; that is, it need not be contraindicated in driving, etc.

How Does Fexofenadine Work?

Fexofenadine belongs to the antihistamine class of drugs that works on peripheral histamine-1 (H-1) receptors; as it works on these receptors, it does not cause drowsiness. These histamine receptors are located,

  • Outside the brain and spinal cord.

  • Gastrointestinal tract.

  • Blood vessels.

  • Respiratory tract.

Histamines are chemical substances that are released by mast cells in response to an allergen. These allergens are responsible for allergic reactions, such as,

  • Swelling of the mucous membranes.

  • Sneezing.

  • Itching.

This drug binds to these histamine receptors and prevents allergic reactions.

Onset Of Action:

Fexofenadine has approximately 33% of oral bioavailability, and it is rapidly absorbed orally and excreted unchanged in urine and bile. This drug is minimally metabolized, and so there are no interactions with the CYP3A4 inhibitor. It generally starts working after 60 minutes of taking the drug and reaches its peak plasma concentration after 11 hours of drug intake. The duration of action is 24 hours, so it is meant to be taken once or twice a day depending on the dosage.

Expiry Date:

Avoid taking this medicine after it expires. Fexofenadine tablet does not work and may lead to serious side effects when it is taken beyond the expiry date. So before taking medicine verify the expiry date printed on the back of the pack or ask your pharmacist or doctor in case of any doubts.

What Is the Dosage and Administration of Fexofenadine?

The dosage and administration of Fexofenadine is decided by,

  • Age of the patient.

  • Weight of the patient.

  • Other medical conditions.

  • Response to the treatment.

Preparations and Doses:

The available forms of Fexofenadine for both adult and children are,

Fexofenadine Doses

Fexofenadine Usual dosage for Adults:

Usual dosage for Adults

Fexofenadine Usual dosage for Children:

Usual dosage for Children

How to Use Fexofenadine?

Fexofenadine is available as tablets, disintegrating tablets (dissolving), and oral suspension (liquid form). Take the tablet or disintegrating tablet or liquid form of this medicine with or without food. When the medicine has been prescribed by the doctor, you should take it as directed by the doctor, that is, every 12 hours.

On taking the OTC (over-the-counter) products to self-treat, you should read all directions on the package label before using this medicine. When you have any doubts or questions, consult your doctor or pharmacist.

On taking the liquid form of this medicine, you should shake the bottle before usage and measure the dose carefully using a dosing syringe or medicine cup or a special measuring device. Avoid using household spoons because you may not get the required dosage.

On the usage of the disintegrating tablet, you should take it on an empty stomach. You should not immediately swallow the disintegrating tablet; instead, you should allow the disintegrating tablet to dissolve on the tongue before swallowing with or without water.

Missed Dose:

It is important to take the missed dose as soon as you remember it, but if it is almost time for the next dose, you can skip the missed dose and start continuing with the regular dosing schedule. In order to compensate for a missed one, do not take a double dose.

What Are the Drug Warnings and Precautions?

Before using Fexofenadine, inform your doctor or pharmacist if you have been allergic to this medicine or you have experienced any other allergies because this drug contains inactive ingredients, which may cause allergic reactions or any other problems. So, it is always better to speak to the doctor or pharmacist to know more information.

1. Before using Fexofenadine, you should tell your doctor or pharmacist about your medical history (present and previous), especially of any kidney diseases.

2. Before any surgery, tell your doctor about all the prescription, nonprescription and herbal products you use to avoid future complications.

3. Avoid removing the tablet from the blister pack right before using.

4. Avoid taking medicine with fruit juices such as grapefruit, apple, or orange because they may decrease the absorption of the drug. So always take medicine (tablets or capsules) with water.

5. Avoid increasing the dose by yourself or taking this medication more often than directed by the pharmacist or doctor because the dosage depends on age, response to the treatment, and medical condition.

6. Avoid taking antacids containing aluminum and magnesium within two hours of taking this drug because they can decrease the absorption of the drug.

7. Ask your doctor about the product safety because liquid products may contain sugar, and disintegrating tablets may contain aspartame. So, this medicine should be cautiously taken when there is a need to limit or avoid certain substances in your diet, that is when you have diabetes, phenylketonuria (PKU), or any other conditions.

8. At the time of pregnancy, this medicine should be used when it is absolutely needed and also discuss the risks and benefits of this medicine before usage with your doctor.

9. It is said that this medication passes into breast milk, so consult with your doctor before breastfeeding.

What Are the Side Effects of Fexofenadine?

  • Common Side Effects:

The following are the common side effects of Fexofenadine, and you should seek a doctor if it worsens and persists for a longer time.

  • Cough.

  • Sinus pain.

  • Headache.

  • Fever.

  • Back pain.

  • Stomach upset.

  • Sore throat.

  • Stuffy nose.

  • Serious Side Effects:

Allergic reactions due to Fexofenadine are rare but stop the drug and get emergency medical help if you come across the following,

  • Rashes.

  • Swelling of the face.

  • Drainage from the ear.

  • Worsening or severe cough.

  • Chills.

  • Ear infection.

  • Severe dizziness.

  • Trouble hearing.

  • Trouble breathing.

  • Itching and swelling of tongue and throat.

  • Fussiness in the child.

What Are the Drug Interactions of Fexofenadine?

1. Drug interactions may change the mechanism and effectiveness of the drug; also, they increase the risk of serious side effects. So, it is better to inform your doctor about all the prescription, nonprescription and herbal drugs you are taking.

2. Do not self-medicate or change the dosage of the drug by yourself; always ask your doctor's approval before usage.

3. It is important to ask your doctor before you take a muscle relaxant, sleeping pill, opioid medication, or other drugs which you take for anxiety and seizures.

4. Fexofenadine is unlikely to interact with drugs that rely upon hepatic metabolism.

5. Fexofenadine is known to interfere with certain laboratory tests, such as skin allergy testing, so there is a high possibility for false test results. So, tell your laboratory personnel and your doctor about the drug you take.

6. Co-administration of Ketoconazole or Erythromycin enhances gastrointestinal absorption of Fexofenadine.

What Are the Common Brand or Trade Names of Fexofenadine?

The common brand names of Fexofenadine are,

  • Allegra.

  • Allegra Allergy 24 Hour.

  • Allegra Hives.

  • Alernex.

  • Allegra ODT.

  • Allegra OTC.

  • Mucinex Allergy.

  • Fenadin.

  • Allegra Allergy 12 Hour.

  • Children’s Allegra Allergy.

  • Afexdine.

  • Fegra.

  • Altiva.

  • Fexo.

  • Aller-Ease.

  • Wal-Fex.

Last reviewed at:
22 Aug 2022  -  7 min read




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