Fexofenadine: Uses, Dosage & Side Effects

What Is Fexofenadine and What Is It Used For?

Fexofenadine hydrochloride is a selective peripheral H1 receptor antagonist belonging to the second-generation antihistamine class. It is the pharmacologically active carboxylic acid metabolite of terfenadine, a first-generation antihistamine that was withdrawn from many markets due to the risk of serious cardiac arrhythmias (torsades de pointes) when combined with certain drugs. Unlike terfenadine, fexofenadine does not undergo significant hepatic metabolism and does not inhibit cardiac potassium channels, giving it an excellent cardiovascular safety profile.

Fexofenadine was first approved by the U.S. Food and Drug Administration (FDA) in 1996 and has since become one of the most widely used antihistamines worldwide. It is available over the counter in most countries under brand names including Allegra, Telfast, and numerous generic formulations. The medication is approved for adults and adolescents aged 12 years and older, and is available in two main tablet strengths: 120 mg for seasonal allergic rhinitis and 180 mg for chronic idiopathic urticaria.

The primary indications for fexofenadine include the symptomatic relief of seasonal allergic rhinitis (hay fever), which presents with sneezing, rhinorrhoea (runny nose), nasal pruritus (itchy nose), nasal congestion, and ocular symptoms including itchy, red, and watery eyes (allergic conjunctivitis). These symptoms are triggered by exposure to airborne allergens such as grass pollen, tree pollen, ragweed pollen, and mould spores, and are mediated by the release of histamine from sensitised mast cells in the nasal and ocular mucosa.

The 180 mg formulation is specifically indicated for the treatment of chronic idiopathic urticaria (also called chronic spontaneous urticaria), a condition characterised by the recurrent appearance of itchy wheals (hives) and/or angioedema without an identifiable external trigger. International guidelines from the European Academy of Allergy and Clinical Immunology (EAACI) and the World Allergy Organization (WAO) recommend second-generation antihistamines as the first-line pharmacological treatment for both conditions.

How Fexofenadine Works

Fexofenadine exerts its therapeutic effect primarily through selective and potent antagonism of peripheral histamine H1 receptors. When the body encounters an allergen, mast cells and basophils release histamine, which binds to H1 receptors on various tissues. This triggers the characteristic cascade of allergic symptoms: vasodilation (leading to nasal congestion and skin redness), increased vascular permeability (causing rhinorrhoea and tissue swelling), smooth muscle contraction, mucus secretion, and stimulation of sensory nerve endings (producing itching and sneezing).

By competitively blocking these H1 receptors, fexofenadine prevents histamine from exerting its effects, thereby reducing or eliminating allergic symptoms. In addition to direct receptor antagonism, fexofenadine has been shown to have anti-inflammatory properties, including inhibition of the release of inflammatory mediators such as interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF), and soluble intercellular adhesion molecule 1 (sICAM-1) from nasal epithelial cells. These additional mechanisms contribute to its effectiveness in reducing both the early and late phases of the allergic response.

A key pharmacological advantage of fexofenadine over many other antihistamines is its minimal penetration of the blood-brain barrier. At therapeutic doses, positron emission tomography (PET) studies have demonstrated that fexofenadine occupies less than 10% of central H1 receptors, compared to approximately 20–50% for cetirizine and over 70% for first-generation antihistamines like diphenhydramine. This low central receptor occupancy explains why fexofenadine is classified as a truly non-sedating antihistamine and why it does not impair cognitive function, psychomotor performance, or driving ability at recommended doses.

Pharmacokinetics

Fexofenadine is rapidly absorbed from the gastrointestinal tract after oral administration, with peak plasma concentrations (Cmax) reached within approximately 1 to 3 hours. The oral bioavailability of fexofenadine is approximately 33%, partly due to limited absorption and the action of efflux transporters (particularly P-glycoprotein) in the intestinal wall. Fexofenadine undergoes minimal hepatic metabolism — approximately 5% of the total dose is metabolised, primarily by intestinal microorganisms rather than hepatic cytochrome P450 enzymes. This is clinically significant because it means that fexofenadine has a very low potential for metabolic drug interactions.

The elimination half-life of fexofenadine is approximately 11 to 15 hours in healthy adults, supporting convenient once-daily dosing. The drug is primarily excreted unchanged in the faeces (approximately 80%) and urine (approximately 11%). Because fexofenadine is not significantly metabolised by the liver and is not primarily eliminated through the kidneys, dose adjustment is generally not required for patients with mild to moderate hepatic or renal impairment, though caution is advised in patients with severe renal insufficiency.

What Should You Know Before Taking Fexofenadine?

Contraindications

Fexofenadine is contraindicated in individuals who have a known hypersensitivity (allergy) to fexofenadine hydrochloride or any of the other ingredients contained in the specific formulation they are using. Cross-reactivity with terfenadine (from which fexofenadine is derived) is theoretically possible, though clinically rare. Patients who experienced allergic reactions to terfenadine should inform their healthcare provider before taking fexofenadine.

Unlike its predecessor terfenadine, fexofenadine does not have absolute cardiac contraindications. Terfenadine was associated with QT interval prolongation and potentially fatal cardiac arrhythmias (torsades de pointes) when combined with CYP3A4 inhibitors such as ketoconazole and erythromycin. Extensive clinical and post-marketing data have confirmed that fexofenadine does not prolong the QT interval even at doses substantially exceeding the recommended therapeutic range, making it safe for patients with pre-existing cardiac conditions who require antihistamine therapy.

Warnings and Precautions

Elderly patients should consult a healthcare provider before starting fexofenadine. While clinical studies have not demonstrated a significant increase in adverse effects in older adults, age-related changes in renal function may affect fexofenadine elimination. Since fexofenadine is partially excreted through the kidneys (approximately 11% of the dose), elderly patients with reduced kidney function may experience slightly higher plasma levels of the drug.

Patients with known kidney or liver problems should discuss fexofenadine use with their healthcare provider. Although fexofenadine undergoes minimal hepatic metabolism, patients with significant hepatic impairment should be monitored. Similarly, patients with moderate to severe renal impairment may require clinical assessment, as the renal clearance of fexofenadine is reduced in these individuals, potentially leading to increased systemic exposure.

Individuals with a current or past history of cardiovascular disease should inform their healthcare provider before using fexofenadine. While fexofenadine has an excellent cardiac safety profile and does not prolong the QT interval at therapeutic doses, the manufacturer advises caution in patients with a history of cardiac arrhythmias as a general precautionary measure. Post-marketing reports of rapid or irregular heartbeat have been received, though a causal relationship has not been established.

If you are scheduled for allergy testing (skin prick tests or intradermal tests), you must stop taking fexofenadine at least 3 days before the test. Antihistamines suppress the skin's allergic response and can produce false-negative results, leading to inaccurate allergy diagnoses. Inform the healthcare professional conducting the test about any recent antihistamine use.

Pregnancy and Breastfeeding

Fexofenadine should only be used during pregnancy if the potential benefit to the mother justifies the potential risk to the foetus. There are limited clinical data on fexofenadine use in pregnant women. Animal reproduction studies (in rats and rabbits) have not demonstrated teratogenic (birth defect-causing) effects, but there are no adequate and well-controlled studies in humans. As with all medications during pregnancy, the decision to use fexofenadine should be made in consultation with a healthcare provider who can weigh the severity of the allergic condition against the theoretical risks of medication exposure.

Fexofenadine is excreted in human breast milk. Studies in lactating women have demonstrated that the drug passes into breast milk, though the exact concentrations and the potential effects on the nursing infant have not been fully characterised. As a precautionary measure, fexofenadine should not be used during breastfeeding unless specifically advised by a healthcare provider. If antihistamine treatment is essential during lactation, the physician can advise on the most appropriate treatment option and whether interruption of breastfeeding is necessary.

Driving and Operating Machinery

Fexofenadine is considered unlikely to affect the ability to drive or operate machinery. Extensive clinical studies, including driving simulation tests and psychomotor performance assessments, have consistently demonstrated that fexofenadine at doses of 120 mg and 180 mg does not impair cognitive function, reaction time, or driving ability compared to placebo. In contrast, first-generation antihistamines such as diphenhydramine and chlorphenamine significantly impair driving performance to a degree comparable to a blood alcohol concentration of 0.05–0.10%.

However, as with any medication, individual responses may vary. Although the risk is extremely low, some patients may experience dizziness or drowsiness as uncommon side effects. Patients should be aware of how they personally respond to fexofenadine before engaging in activities that require full alertness, particularly during the initial days of treatment.

Sodium Content

Fexofenadine film-coated tablets contain less than 1 mmol (23 mg) of sodium per tablet, meaning they are essentially sodium-free. This is relevant for patients on sodium-restricted diets, such as those with heart failure, hypertension, or kidney disease. The negligible sodium content means that fexofenadine can be used safely by these patient groups without concern about sodium intake from the medication itself.

How Does Fexofenadine Interact with Other Drugs?

Fexofenadine has a distinct pharmacokinetic profile that differs from most other medications. Because it undergoes minimal hepatic metabolism and is not significantly processed by the cytochrome P450 enzyme system, fexofenadine has a low potential for the type of metabolic drug interactions that are common with many other drugs. However, fexofenadine is a substrate for P-glycoprotein (P-gp) and organic anion-transporting polypeptides (OATPs), membrane transport proteins that play a key role in its absorption and elimination. Drugs that inhibit or induce these transporters can alter fexofenadine plasma levels.

It is important to inform your healthcare provider or pharmacist about all medications you are currently taking, including prescription drugs, over-the-counter medications, herbal supplements, and vitamins, to ensure there are no potential interactions with fexofenadine.

Antacid Interactions

Aluminium and magnesium hydroxide-containing antacids represent the most clinically important interaction with fexofenadine. When taken simultaneously, these antacids form a complex with fexofenadine in the gastrointestinal tract, significantly reducing its absorption and consequently its plasma levels and therapeutic effectiveness. To avoid this interaction, patients should take fexofenadine at least 2 hours before or after any aluminium or magnesium-containing antacid. Calcium-based antacids do not appear to interact with fexofenadine to the same degree.

Fruit Juice Interactions

An important and often overlooked interaction involves fruit juices. Grapefruit juice, orange juice, and apple juice have been shown to reduce fexofenadine absorption by inhibiting organic anion-transporting polypeptides (OATPs) in the intestinal wall. Studies have demonstrated reductions in fexofenadine bioavailability of up to 36% when taken with large volumes of grapefruit juice. For this reason, fexofenadine should be taken with water rather than fruit juice to ensure optimal absorption and therapeutic efficacy.

Cardiovascular Safety with Interacting Drugs

A critically important clinical point is that unlike its predecessor terfenadine, fexofenadine does not cause QT prolongation or cardiac arrhythmias even when its plasma levels are significantly increased by interacting drugs such as erythromycin or ketoconazole. Clinical studies specifically designed to assess this risk have demonstrated no clinically significant changes in the QT interval when fexofenadine was co-administered with these drugs, even though fexofenadine plasma levels increased 2 to 3-fold. This excellent cardiac safety profile is a major advantage of fexofenadine over terfenadine and is one of the reasons fexofenadine replaced terfenadine on the market.

What Is the Correct Dosage of Fexofenadine?

Fexofenadine should always be taken exactly as described in the patient information leaflet or as directed by a healthcare provider or pharmacist. The film-coated tablets should be swallowed whole with a glass of water. Fexofenadine is recommended to be taken before meals, as food — particularly high-fat meals — may reduce the rate and extent of absorption by up to 30%. Taking the medication on an empty stomach or at least 15 minutes before eating ensures optimal bioavailability.

Adults

For adults and adolescents aged 12 years and over, the standard dose for seasonal allergic rhinitis is one 120 mg film-coated tablet taken once daily. This dose has been shown in large-scale clinical trials to provide statistically significant and clinically meaningful relief from all major hay fever symptoms, including nasal congestion, rhinorrhoea, sneezing, and ocular pruritus. The onset of symptom relief typically occurs within 1 hour of administration, with the full therapeutic effect maintained for 24 hours, allowing convenient once-daily dosing.

For the treatment of chronic idiopathic urticaria, the recommended dose is one 180 mg film-coated tablet taken once daily. Clinical studies have demonstrated that this higher dose is more effective for urticaria than the 120 mg dose, providing significant reduction in the number, size, and itchiness of wheals as well as overall improvement in quality of life for patients with this condition.

Children

The 120 mg and 180 mg film-coated tablet formulations are not recommended for children under 12 years of age. In some countries, lower-dose formulations (such as 30 mg tablets or oral suspension) are available for children aged 6 to 11 years, typically dosed at 30 mg twice daily. For children aged 2 to 5 years, an oral suspension may be available in certain markets. Parents and caregivers should consult a healthcare provider or pharmacist for age-appropriate fexofenadine formulations and dosing guidance for their child.

Elderly Patients

No specific dose adjustment is required for elderly patients. Clinical pharmacokinetic studies have not demonstrated clinically significant differences in fexofenadine disposition between younger and older adults when renal function is comparable. However, since kidney function naturally declines with age, elderly patients should discuss fexofenadine use with their healthcare provider, particularly if they have known or suspected renal impairment. Monitoring for side effects is advisable, as higher plasma levels may occur in elderly patients with reduced renal clearance.

Missed Dose

If you forget to take a dose of fexofenadine, take it as soon as you remember, unless it is nearly time for your next scheduled dose. In that case, skip the missed dose entirely and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. Missing a single dose may result in a temporary return of allergy symptoms but does not pose any medical risk. If you consistently forget doses, consider setting a daily reminder or taking the medication at the same time each day to establish a routine.

Overdose

Symptoms that have been reported following fexofenadine overdose include dizziness, drowsiness, fatigue, and dry mouth. In clinical studies, single doses of up to 800 mg and repeated doses of up to 690 mg twice daily for one month were administered to healthy volunteers without development of clinically significant adverse effects. This wide therapeutic index contributes to fexofenadine's overall safety profile. There is no specific antidote for fexofenadine overdose; treatment is supportive and symptomatic. Haemodialysis does not effectively remove fexofenadine from the blood.

Duration of Treatment

For self-medication with fexofenadine, you should consult a healthcare provider if your symptoms do not improve within 7 days of starting treatment, as this may indicate a different underlying condition that requires medical assessment. Fexofenadine should not be used continuously for more than 3 months without consulting a doctor, who can evaluate whether ongoing treatment remains appropriate and whether alternative management strategies should be considered. Many patients with seasonal allergies use fexofenadine throughout the pollen season (typically several weeks to a few months) without adverse effects.

What Are the Side Effects of Fexofenadine?

Like all medicines, fexofenadine can cause side effects, although not everyone will experience them. In clinical trials, the overall incidence of adverse effects with fexofenadine was comparable to placebo, reflecting the drug's excellent tolerability profile. The side effects listed below have been reported during clinical trials and post-marketing surveillance, and are categorised by their frequency of occurrence.

Understanding the Side Effect Profile

It is important to put fexofenadine's side effect profile into context. In large controlled clinical trials, the incidence of headache with fexofenadine 120 mg was approximately 7.8%, compared to 7.1% with placebo, a difference that is not clinically significant. Similarly, the incidence of drowsiness was approximately 1.3% with fexofenadine compared to 0.7% with placebo. These numbers demonstrate that most of the commonly reported side effects occur at rates very similar to placebo, suggesting that many reported effects may not actually be caused by the medication itself.

Fexofenadine's side effect profile is notably favourable compared to first-generation antihistamines (which cause significant sedation and anticholinergic effects) and even compared to some other second-generation antihistamines. Unlike cetirizine, which causes drowsiness in up to 10% of users, fexofenadine causes drowsiness at rates essentially indistinguishable from placebo. Unlike diphenhydramine and chlorphenamine, fexofenadine does not cause significant dry mouth, constipation, urinary retention, or blurred vision from anticholinergic activity.

Cardiovascular Side Effects

Post-marketing reports have included cases of tachycardia (rapid heart rate) and palpitations. However, these reports are rare and a direct causal relationship with fexofenadine has not been established. Importantly, comprehensive QT studies have confirmed that fexofenadine does not prolong the QT interval at therapeutic or supra-therapeutic doses. This is a critical safety distinction from terfenadine and represents one of the primary reasons fexofenadine was developed as its replacement. Patients who experience persistent or troublesome heart rhythm changes while taking fexofenadine should consult their healthcare provider.

Reporting Side Effects

It is important to report suspected side effects after a medication has been authorised for use. Reporting helps regulatory agencies continuously monitor the benefit-risk balance of medicines. In the United Kingdom, adverse reactions can be reported to the Medicines and Healthcare products Regulatory Agency (MHRA) through the Yellow Card Scheme. In the United States, reports can be filed with the FDA through the MedWatch programme. In the European Union, national pharmacovigilance systems accept reports from both healthcare professionals and patients. You can also report side effects to the marketing authorisation holder listed on the packaging.

How Should You Store Fexofenadine?

Fexofenadine film-coated tablets should be kept out of the sight and reach of children to prevent accidental ingestion. Store the medication at room temperature in its original packaging. No special storage conditions, such as refrigeration or protection from light or moisture, are required for fexofenadine tablets, making them convenient for everyday use and travel.

Do not use fexofenadine after the expiry date stated on the carton and blister packaging. The expiry date refers to the last day of the indicated month. Using expired medication may result in reduced efficacy, as the active ingredient may have degraded over time. If you notice any change in the appearance of the tablets (discolouration, crumbling, or unusual smell), do not take them and consult your pharmacist.

Unused or expired medications should not be disposed of via household waste or flushed down the toilet or drain, as pharmaceutical residues can contaminate water supplies and harm the environment. Instead, return unused medicines to a pharmacy or utilise a local medication take-back programme. Many pharmacies and healthcare facilities worldwide offer free disposal services for unwanted medications. These measures help protect the environment and prevent accidental exposure to others, particularly children and pets.

What Does Fexofenadine Contain?

Active Ingredient

The active pharmaceutical ingredient is fexofenadine hydrochloride. Two strengths are available: each 120 mg tablet contains 120 mg of fexofenadine hydrochloride (equivalent to approximately 112 mg of fexofenadine base), and each 180 mg tablet contains 180 mg of fexofenadine hydrochloride (equivalent to approximately 168 mg of fexofenadine base). Fexofenadine hydrochloride is a white to off-white crystalline powder that is freely soluble in methanol and dimethyl sulfoxide, slightly soluble in chloroform and water, and practically insoluble in hexane. Its molecular formula is C₃₂H₃₉NO₄·HCl, with a molecular weight of 538.12 g/mol.

Fexofenadine is the active metabolite of terfenadine and exists as a racemic mixture. The pharmacological activity is attributed to the drug's ability to selectively antagonise peripheral H1 histamine receptors. Its chemical structure includes a diphenylmethyl piperidine backbone that is responsible for its receptor-binding properties.

Inactive Ingredients (Excipients)

The inactive ingredients in a typical fexofenadine film-coated tablet formulation include:

• Microcrystalline cellulose — a filler and binder that provides bulk and structural integrity to the tablet
• Croscarmellose sodium — a super-disintegrant that helps the tablet break apart rapidly in the digestive tract
• Maize starch (corn starch) — serves as a binder and disintegrant
• Povidone (polyvinylpyrrolidone) — a binding agent used during tablet granulation
• Magnesium stearate — a lubricant that prevents the tablet from sticking to machinery during production
• Hypromellose (E464) — forms the film coating that protects the tablet and aids swallowing
• Titanium dioxide (E171) — a white colouring agent in the film coating
• Macrogol 400 and Macrogol 4000 (polyethylene glycol) — plasticisers used in the film coating
• Yellow iron oxide (E172) and Red iron oxide (E172) — colouring agents that give the tablet its characteristic peach colour

Appearance and Pack Sizes

Fexofenadine 120 mg tablets are typically peach-coloured, oblong, film-coated tablets, smooth on both sides, approximately 15.1 mm in length and 6.6 mm in width. Fexofenadine 180 mg tablets are also peach-coloured but may be slightly larger. Tablets are supplied in aluminium/PVC blister packs. Available pack sizes commonly include 2, 7, 10, 15, 20, and 30 tablets, though not all sizes may be marketed in all countries. The specific appearance may vary between different manufacturers and brands.

References

This article is based on the following international medical guidelines, regulatory documents, and peer-reviewed sources:

1. European Medicines Agency (EMA). Summary of Product Characteristics — Fexofenadine hydrochloride 120 mg and 180 mg film-coated tablets. Updated 2024. Available from: www.ema.europa.eu
2. U.S. Food and Drug Administration (FDA). Allegra (fexofenadine hydrochloride) — Drug Label Information. Available from: www.accessdata.fda.gov
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6. British National Formulary (BNF). Fexofenadine hydrochloride monograph. National Institute for Health and Care Excellence (NICE). Available from: bnf.nice.org.uk
7. Simons FER, Simons KJ. Histamine and H1-antihistamines: celebrating a century of progress. J Allergy Clin Immunol. 2011;128(6):1161-1174. doi:10.1016/j.jaci.2011.09.005
8. Hiraoka K, et al. Quantitative analysis of the central H1 receptor occupancy of fexofenadine by PET. Br J Clin Pharmacol. 2015;79(3):478-485.
9. Dresser GK, et al. Fruit juices inhibit organic anion transporting polypeptide-mediated drug uptake to decrease the oral availability of fexofenadine. Clin Pharmacol Ther. 2002;71(1):11-20.
10. European Academy of Allergy and Clinical Immunology (EAACI). Guideline on the use of antihistamines in the treatment of allergic diseases. 2023.

Editorial Team

Last medical review: January 22, 2026 | Next scheduled review: July 2026