Loratadine
A long-acting second-generation antihistamine for hay fever and chronic hives that rarely causes drowsiness.
Drug card
- How it works
- Blocking peripheral H1 receptors while largely staying out of the brain
- Used for
- Hay fever and allergic rhinitis
- Chronic hives (chronic idiopathic urticaria)
- Known for
- Headache
- Its name
- -tadine means a tricyclic H1 antihistamine (loratadine type)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does loratadine work?
A tricyclic antihistamine with selective activity at peripheral H1 receptors and no clinically significant sedative or anticholinergic effect at usual doses. Extensive first-pass metabolism by CYP3A4 and CYP2D6 forms desloratadine, an active metabolite that provides much of the effect, which lasts more than 24 hours.
Like other second-generation antihistamines: Second-generation antihistamines selectively block peripheral H1 receptors, so histamine can no longer make small vessels leak and swell or trigger itching, sneezing and a runny nose. They pass poorly into the brain and have little affinity for other receptors, so at usual doses they cause little drowsiness and almost no anticholinergic effect, and one dose lasts about a day.
Uses
What is loratadine used for?
- Hay fever and allergic rhinitis
- Chronic hives (chronic idiopathic urticaria)
Side effects
Side effects of loratadine
- HeadacheKnown for
- Drowsiness (uncommon)
- Tiredness
- Increased appetite and weight gain
- Insomnia
- Nervousness in children
- Dry mouth
- Nausea and gastritis
- Fast heartbeat and palpitations (very rare)
- Abnormal liver function (very rare)Serious
- Seizures (very rare)Serious
- Allergic reactions, including anaphylaxisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Severe liver impairment slows its clearance, so a lower starting dose is used.
- CYP3A4 and CYP2D6 inhibitors such as ketoconazole, erythromycin and cimetidine raise its levels.
- It is stopped at least 48 hours before allergy skin tests, which it can blunt.
- Above the usual dose it can cause drowsiness.
Good to know: In psychomotor tests it does not add to the effects of alcohol, unlike first-generation antihistamines.
Remember it
A way to remember it
The second generation stays out of your head.
Newer antihistamines barely cross the blood-brain barrier and ignore muscarinic receptors, so they ease allergy with little drowsiness or dry mouth; cetirizine is the one most likely to make people sleepy.
Written for biofideX
Its name
-tadine means tricyclic H1 antihistamine (loratadine type)
Loratadine and desloratadine, H1 antihistamines with a three-ring core, share it. Don't confuse it with -tidine, the H2 blockers; amantadine, an antiviral, fits only by chance.
- Every drug name stem
Its class
Second-generation antihistamines
Other second-generation antihistamines with a card:
Easily mixed up with first-generation antihistamines, H2 receptor antagonists and leukotriene receptor antagonists.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Loratadine tablets: label (DailyMed)
- Loratadine tablets: SmPC (emc)
- Loratadine (NCI Thesaurus)
- Loratadine (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Lungs and allergy
Loratadine is one of 16 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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