Desloratadine

Desloratadine is the active metabolite of loratadine, a once-daily non-sedating second-generation H1 antihistamine used for allergic rhinitis and chronic urticaria. It does not treat anaphylaxis.

Classification. Second-generation H1 antihistamine.

Mechanism. Selective peripheral H1 receptor antagonist with additional weak anti-inflammatory effects.

Pharmacokinetics. Onset within 1 hour, duration 24 hours. Half-life about 27 hours. Metabolised to 3-hydroxydesloratadine by UGT2B10 and CYP2C8. A slow-metaboliser phenotype exists and is more common in people of African ancestry, with higher exposure but no clinically important change in safety.

First-line, allergic rhinitis and urticaria, adults and adolescents from 12 years. 5 mg once daily.

Children. 6 to 11 years: 2.5 mg once daily. 1 to 5 years: 1.25 mg once daily. 6 to 11 months: 1 mg once daily where licensed. Under 6 months: not advised.

Specialist, chronic spontaneous urticaria. Specialists may use up to 4 times the usual dose off label.

Emergency. Not used.

Titration and loading. None.

Contraindications. Hypersensitivity to desloratadine or loratadine.

Serious adverse effects. Rare anaphylaxis, tachycardia and palpitations, seizures, hallucinations, liver injury.

Common adverse effects. Fatigue, dry mouth, headache, pharyngitis.

Interactions. No clinically important interactions with ketoconazole, erythromycin or azithromycin. Alcohol does not add to impairment at usual doses.

Common prescribing errors. Doubling with loratadine, because loratadine converts to desloratadine. Using for nasal congestion alone.

Special groups.

• Pregnancy: limited data; loratadine is preferred. Breastfeeding: excreted in milk; avoid.

• Older adults: no adjustment.

• Kidney and liver impairment: in severe impairment, 5 mg every other day.

• East Africa: slower metabolism may occur more often in people of African ancestry; no dose change is advised. Widely available.

Formulations. Tablets 5 mg, syrup 0.5 mg/mL.

Administration. Once daily, with or without food.

Baseline. Symptom and urticaria score.

Monitoring. Control and adverse effects at 2 to 4 weeks.

Stop and reduce rules. Reduce frequency in severe kidney or liver impairment. Therapeutic drug monitoring is not used.

Referral and escalation. Refer for urticaria not controlled by antihistamines, angioedema or suspected anaphylaxis.