Loratadine
H1 antihistamines
H1 antihistamines
A once-daily second-generation antihistamine for hay fever and allergic itch that rarely causes drowsiness.
Quick facts
- Group
- H1 antihistamines
- Target
- Histamine H1 receptor
- Used for
- Allergic rhinitis · Itchy · Hives
- Key effects
- Headache · Mild drowsiness or tiredness · Dry mouth
- Monitor
- Symptom relief · Drowsiness in sensitive patients
- ATC
- R06AX13
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows desloratadine bound to the human histamine H1 receptor (cryo-electron microscopy); desloratadine is the active metabolite of loratadine.
Loratadine is a long-acting second-generation H1 antihistamine. It and its active metabolite desloratadine act as inverse agonists at peripheral H1 receptors, blocking histamine-driven sneezing, itching, runny nose, watery eyes and wheals. Because it is poorly able to cross the blood–brain barrier, it has little sedative or anticholinergic effect at usual doses.
- Loratadine is absorbed and converted in the liver to desloratadine
- Both bind peripheral H1 receptors and keep them inactive
- Histamine can no longer cause itch, sneezing and leaky vessels
- Little reaches the brain, so sedation is rare
Indications
- Allergic rhinitis (sneezing, runny and itchy nose) Allergic rhinitis →
- Itchy, watery eyes of allergic conjunctivitis Conjunctivitis →
- Hives (urticaria) Urticaria and angioedema →
Adverse effects
Common
- Headache
- Mild drowsiness or tiredness in some people
- Dry mouth
Contraindications
- Hypersensitivity to loratadine or desloratadine
- Caution in significant liver or kidney disease
Key interactions
- Desloratadine and other H1 antihistamines
- Duplicate H1 blockade (desloratadine is the same active substance): not combined
- Alcohol, benzodiazepines, opioids and other CNS depressants
- Additive sedation and slowed breathing
What is monitored
- Symptom relief
- Drowsiness in sensitive patients
Administration and safety
- Oral tablets, orally disintegrating tablets or syrup, once a day
- Combination products with pseudoephedrine exist: check the label so the decongestant is not taken by someone who should avoid it
Pregnancy and breastfeeding
Loratadine is one of the antihistamines with the most pregnancy experience; whether to use it is decided with the clinician.
Nursing care
- Ask about allergy triggers and other antihistamines or cold products already used
- Explain that it does not replace epinephrine in a severe allergic reaction
- Teach that drowsiness is uncommon but possible
Pharmacokinetics
- Absorption
- Well absorbed by mouth
- Metabolism
- Extensive first-pass metabolism in the liver (CYP3A4, CYP2D6) to the active metabolite desloratadine
- Elimination
- As metabolites in urine and faeces
- Onset and duration
- Relief within hours, lasting about a day
Test yourself
Think of the answer, then tap the question to see it.
What is the active metabolite of loratadine?
Desloratadine.
Why does loratadine cause less sedation than diphenhydramine?
It crosses the blood–brain barrier poorly, so it blocks few central H1 receptors.
A patient with anaphylaxis has taken loratadine. Is that enough treatment?
No; intramuscular epinephrine is the first treatment, antihistamines only help the skin symptoms.
Connections
← Back to the class: H1 antihistamines
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Loratadine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - DESLORATADINE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.