Fexofenadine – Dosage

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 terfenadine7 and is administered as a racemic mixture in which both enantiomers display approximately equivalent antihistamine activity.

Properties and Characteristics of Fexofenadine

Drug class	Antihistamine
Brand Names	Allegra Allergy, Allegra Hives,
Synonyms	Carboxyterfenadine, Fexofenadina, Fexofenadine, Terfenadine acid metabolite, Terfenadine carboxylate, Terfenadine-COOH
Molecular Formula	C32H39NO4
Molecular Weight	501.7 g/mol
IUPAC Names	2-[4-[1-hydroxy-4-[4-[hydroxy(diphenyl)methyl]piperidin-1-yl]butyl]phenyl]-2-methylpropanoic acid
Structural formula of main components
Pure active ingredient	Fexofenadine
Appearance	Crystals
Melting Point	142.5°C
Solubility	Slightly soluble in water
Excretion	Fexofenadine elimination are biliary and renal
Available as	Capsule, Suspension and Tablet
Storage	Stored at controlled room temperature between 20-25 °C
Prescription	Prescription is required

Uses of Fexofenadine

Allergic conditions such as hay fever (an allergy caused by pollen or dust), conjunctivitis (red, itchy eye), eczema (dermatitis), hives (red, raised patches or dots), reactions to insect bites and stings and some food allergies.

Fexofenadine side effects

Get emergency medical help if you have signs of an allergic reaction to fexofenadine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Fexofenadine may cause serious side effects. Stop using fexofenadine and call your doctor at once if you have:

• Flu-like symptoms (fever, chills, unusual tiredness);
• New or worsening cough;
• Pain; or
• Signs of an ear infection–fever, ear pain or full feeling, trouble hearing, drainage from the ear, fussiness in a child.

Common side effects of fexofenadine may include:

• Headache;
• Back Pain; Or
• Cold symptoms such as stuffy nose, sinus pain, sore throat.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Mechanism of action

The H1 histamine receptor is responsible for mediating hypersensitivity and allergic reactions. Exposure to an allergen result in degranulation of mast cells and basophils, which then release histamine and other inflammatory mediators. Histamine binds to, and activates, H1 receptors, which results in the further release of pro-inflammatory cytokines, such as interleukins, from basophils and mast cells. These downstream effects of histamine binding are responsible for a wide variety of allergic symptoms, such as pruritus, rhinorrhea, and watery eyes.

Fexofenadine is considered an “inverse agonist” of the H1 receptor because it binds to and stabilizes the inactive form of the receptor, preventing its activation and subsequent downstream effects. It has a potent and selective affinity for H1 receptors, and there is no evidence that it carries antidopaminergic, antiserotonergic, anticholinergic, sedative, or adrenergic blocking activity. Fexofenadine does not cross the blood-brain barrier and thus is unlikely to cause significant CNS effects.

What are the drugs interact with Fexofenadine?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

Severe Interactions of fexofenadine include:

• Grapefruit

Serious Interactions of fexofenadine include:

• Isocarboxazid
• Ivacaftor
• Tranylcypromine

Moderate Interactions of fexofenadine include:

• Bosutinib
• Crizotinib
• Crofelemer
• Cyclosporine
• Daclatasvir
• Eliglustat
• Eluxadoline
• Juice (fruit)
• Lomitapide
• Lurasidone
• Nefazodone
• Ombitasvir/paritaprevir/ritonavir
• Phenelzine
• Ponatinib
• Quinidine
• Sofosbuvir/velpatasvir
• Vemurafenib

Fexofenadine has mild interactions with at least 39 different drugs.

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns or for more information about this medicine.

Dosing

The dose of this medicine will be different for different patients. Follow your doctor’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For symptoms of hay fever

For oral dosage form (capsules, tablets):

• Adults and children 12 years of age and older—60 milligrams (mg) two times a day, or 180 mg once a day.
• Children 6 to 11 years of age—30 mg two times a day.
• Children 4 to 6 years of age—Use and dose must be determined by your doctor.
• Children and infants up to 4 years of age—Use is not recommended.

For oral dosage form (disintegrating tablets):

• Children 6 to 11 years of age—30 milligrams (mg) two times a day, on an empty stomach.
• Children 4 to 6 years of age—Use and dose must be determined by your doctor.
• Children and infants up to 4 years of age—Use is not recommended.

For oral dosage form (suspension):

• Children 4 to 11 years of age—30 milligrams (mg) or 5 milliliters (mL) two times a day.
• Children younger than 4 years of age—Use and dose must be determined by your doctor.

For symptoms of chronic hives

For oral dosage form (capsules, tablets):

• Adults and children 12 years of age and older—60 milligrams (mg) two times a day, or 180 mg once a day.
• Children 4 to 11 years of age—30 mg two times a day.
• Children younger than 4 years of age—Use and dose must be determined by your doctor.

For oral dosage form (disintegrating tablets):

• Children 4 to 11 years of age—30 milligrams (mg) two times a day, on an empty stomach.
• Children younger than 4 years of age—Use and dose must be determined by your doctor.

For oral dosage form (suspension):

• Children 4 to 11 years of age—30 milligrams (mg) or 5 milliliters (mL) two times a day.
• Children 6 months to 4 years of age—15 mg or 2.5 mL two times a day.
• Children younger than 6 months of age—Use and dose must be determined by your doctor.

Overdose

The safety profile of fexofenadine is quite favorable, as no cardiovascular or sedative effects have been shown to occur even when taking 10 times the recommended dose. Research on humans ranges from a single 800-mg dose, to a twice-daily, 690-mg dose for a month, with no clinically significant adverse effects, when compared to a placebo. No deaths occurred in testing on mice, at 5000 mg/kg body weight, which is 110 times the maximum recommended dose for an adult human. If overdose were to occur, supportive measures are recommended. Theoretically, an overdose could present as dizziness, dry mouth, and/or drowsiness, consistent with an exaggeration of the usual side effects. Hemodialysis does not appear to be an effective means of removing fexofenadine from the blood.

Warnings

General warnings

Drowsiness: Fexofenadine may cause dizziness. Do not drive vehicles or operate machines after taking this medicine.

Use in children: Avoid using Fexofenadine in infants less than 6 months of age.

The tablet form of fexofenadine is not recommended for use in children below 12 years of age due to the lack of safety and efficacy data.

Warnings for special population

Fexofenadine and pregnancy

Fexofenadine is not usually recommended if you’re pregnant as there is not a lot of information about its use in pregnancy.

Other antihistamines may be more suitable as better safety information is available.

If you think that you need to take fexofenadine in pregnancy, talk to your doctor or pharmacist who will help you decide, or who may recommend other medicines for you.

Fexofenadine and breastfeeding

If your doctor or health visitor says your baby is healthy, you can take fexofenadine while breastfeeding.

There is very little information available, but it shows that only tiny amounts get into breast milk. It is unlikely to cause any side effects in your baby.

If you’re breastfeeding or planning to breastfeed, talk to your doctor or pharmacist, as other antihistamines called loratadine and cetirizine might be better while you’re breastfeeding.

If your baby is not feeding as well as usual, seems unusually sleepy, or seems irritable, or if you have any other concerns about your baby, talk to your doctor, pharmacist, health visitor or midwife.