Loratadine (lor-a’ti-deen) is a non-sedating second generation H1-antagoist usually used to manage allergic rhinitis and urticaria. It is on the World Health Organization’s List of Essential Medicines. It is available as oral tablets, oral suspension and a syrup and is also available in combination with pseudoephedrine. It is available by prescription and as an over-the-counter.
In the USA, the first television advertisement for direct to consumer marketing of a prescription drug was for loratadine in in 1983. It was controversial. The response of the FDA was to bring in strong regulations, especially the need to disclose side effects in the advertising.
Mechanism of action:
Acts as a selective inverse agonist of peripheral histamine H1 receptors. Does not cross the blood-brain barrier, so has no central sedading effects.
Pharmacokinetics:
Well absorbed orally with bioavailability of almost 100% and protein binding is 97–99%.
It is metabolized by isoenzymes of the cytochrome P450 system in the liver.
Peak effect occurs after 1–2 hours and elimination half-life is 8 hours.
Its metabolite desloratadine has a half-life of 27 hours (which accounts for the long lasting effects of the drug).
Excretion is 40% into urine and 40% into the feces.
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Brand names: Claritin, Alavert, Allerclear, Diphen, Loradamed, Wal-itin, Claratyne, Tavist ND, and many others.
Chemical formula: C22H23ClN2O2
Dosage:
Usual adult dose: 10mg orally once a day.
Contraindication:
Liver disorders (or use a lower dose).
Children under 2 yrs of age.
Acute asthma.
Cautions:
Asthma or COPD due to its anticholinergic effects
USA, category B in pregnancy.
Interactions:
Drugs that inhibit the CYP3A4 enzyme (eg ketoconazole, erythromycin, cimetidine, grapefruit juice) increase the plasma levels of loratadine.
Side effects:
Common: drowsiness; xerostomia (dry mouth); headache, dizziness
Less common: allergic reactions; seizures; liver problems, mydriasis (dilated pupils)
Don’t confuse with:
Lovastatin; lorazepam
In Australia, loratadine is on the National Podiatry Scheduled Medicines List for use by authorised Podiatrists.
Examples of other H1 Antagonists (Anti-histamines):
| Highly Sedative: | Moderately Sedative: | Mildly Sedative: | Not Sedative: |
| Promethazine Hydroxyzine Dimenhydinate | Pheniramine Meclozine Cinnarizine | Triprolidine Clemastine Chlorpheniramine Dexchlorpheniramine | Desloratadine Fexofenadine Loratadine |
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