Loratadine: A non-sedating second-generation H1 antihistamine

What it is

Loratadine is a second-generation H1 antihistamine, available without a prescription in Spain. It is one of the most dispensed antihistamines in the world because of its safety profile: effective against allergy symptoms with minimal sedation and a 24-hour duration.

Its active metabolite, desloratadine, is also marketed as an active substance in its own right, with a very similar profile.

Selective blockade of the peripheral H1 receptor

Loratadine competitively blocks histamine H1 receptors:

It blocks peripheral H1 receptors → it reduces itching, sneezing, runny nose and watery eyes.
It barely reaches the brain (P-glycoprotein pumps it out at the blood–brain barrier) → minimal sedation.
It has no relevant anticholinergic effect: no dry mouth or urinary retention.
It is not a bronchodilator: it does not treat the bronchospasm of allergic asthma.
It acts on established symptoms but also has a preventive effect if taken before allergen exposure.

At the counter

When to recommend it

Seasonal (pollen) or perennial (dust mites, pet hair) allergic rhinitis
Acute and chronic urticaria
Allergic conjunctivitis (add antihistamine eye drops for better eye relief)
Allergic contact dermatitis with itching
First option for people with allergies who drive or operate machinery
In pregnancy and breastfeeding it is one of the antihistamines with the most data (the decision is the doctor's)

When not to

It does not work in severe food allergies or anaphylaxis (adrenaline is needed)
It is not a bronchodilator: it does not replace salbutamol in an asthma attack
In severe urticaria a higher dose or a combination may be needed: that requires medical assessment
It is not the first option if a sedative effect is wanted (for example, intense night-time itching that prevents sleep)

What to say at the counter. The key advantage of loratadine over classic antihistamines (diphenhydramine, dexchlorpheniramine) is that it does not cause significant drowsiness. That question —do you drive, operate machinery, need to concentrate?— decides which antihistamine to recommend.

Warnings

Caution GRAPEFRUIT: grapefruit juice inhibits CYP3A4 and can raise loratadine levels. Although the clinical effect is mild, tell the patient.
Caution LIVER FAILURE: in severe liver disease, the dose is given on alternate days.
Worth knowing INDIVIDUAL SEDATION: although statistically non-sedating, a small proportion of patients report drowsiness. If it happens, consider switching to bilastine or desloratadine.
Worth knowing VARIABLE EFFICACY: in severe allergic rhinitis or chronic urticaria it may not be enough on its own. Adding a nasal corticosteroid in moderate to severe rhinitis gives much better results.

Pharmacokinetics

Absorption: Oral: rapid absorption. Peak plasma level at 1–1.5 hours. Food slightly increases absorption but not clinical efficacy.
Distribution: High plasma protein binding (97–99%). Wide distribution in peripheral tissues. Little penetration into the CNS: hence its low sedation.
Metabolism: Extensive hepatic metabolism via CYP3A4 and CYP2D6. It is converted into desloratadine, its active metabolite. Caution with CYP3A4 inhibitors (ketoconazole, erythromycin, grapefruit juice), which raise its levels.
Elimination: Renal and faecal, as metabolites. Half-life: 8–12 hours (loratadine) and 17–28 hours (desloratadine) → a 24-hour effect with a single daily dose.

Second-generation vs first-generation antihistamines

Aspect	2nd generation (loratadine)	1st generation (diphenhydramine, dexchlorpheniramine)
Sedation	Minimal or none	High (crosses the blood–brain barrier)
Duration	24 hours (1 dose)	4–6 hours (3–4 doses)
Anticholinergic effect	Minimal	Significant (dry mouth, retention)
Driving	Generally compatible	Not advised
Use in older people	Preferable	Avoid (falls, confusion)
Occasional night-time use	Valid	May help because of the sedative effect

Second generation (loratadine, cetirizine, bilastine) is the first choice in practically every case. First generation only has an advantage when sedation is the goal (insomnia from itching). In older people, always avoid the sedating ones.

Self-assessment

Three questions. When you check your answers you will see the explanation for each one.

A lorry driver with allergic rhinitis asks which antihistamine they can take. Which do you choose? Loratadine, because it does not cause significant sedation Dexchlorpheniramine, because it acts sooner Diphenhydramine, because it is the most effective
Does loratadine cause dry mouth or urinary retention? Only in people over 65 No, because its anticholinergic effect is minimal Yes, like all antihistamines
When is loratadine alone not enough for allergic rhinitis? Never, loratadine is always enough Always, it has to be combined with an antibiotic In moderate to severe rhinitis, where adding a nasal corticosteroid helps

Training content. It does not replace the summary of product characteristics or clinical judgement.

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