Loratadine

Loratadine is a non-sedating second-generation H1 antihistamine used for allergic rhinitis and chronic urticaria. It is the antihistamine with the most pregnancy and breastfeeding experience and has the least sedation. It does not relieve nasal congestion on its own and does not treat anaphylaxis.

Classification. Second-generation H1 antihistamine.

Mechanism. Selective peripheral H1 receptor inverse agonist, with little central nervous system penetration.

Pharmacokinetics. Onset 1 to 3 hours, duration 24 hours. Metabolised mainly by CYP3A4 and CYP2D6 to desloratadine (active). Half-life about 8 hours for loratadine and about 27 hours for desloratadine. Excreted in urine and faeces.

First-line, allergic rhinitis and urticaria, adults and children over 30 kg or from 12 years. 10 mg once daily.

Children 2 to 11 years. Body weight over 30 kg: 10 mg once daily. 30 kg or less: 5 mg once daily. Under 2 years: not advised.

Alternative. Intranasal corticosteroid is more effective for moderate to severe rhinitis.

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.

Serious adverse effects. Rare anaphylaxis, severe liver injury, seizures, arrhythmia at overdose.

Common adverse effects. Headache, dry mouth, fatigue, drowsiness (uncommon at 10 mg).

Interactions. CYP3A4 and CYP2D6 inhibitors (ketoconazole, erythromycin, cimetidine) raise levels without clinically important ECG changes. Combination products with pseudoephedrine add hypertension and insomnia.

Common prescribing errors. Prescribing combination decongestant products to people with hypertension. Using for nasal congestion alone. Duplicating with other antihistamines.

Special groups.

• Pregnancy: acceptable, and the usual first choice. Breastfeeding: acceptable; small amounts in milk and low sedation.

• Older adults: no adjustment.

• Kidney impairment: GFR under 30 mL/min, 10 mg every other day. Liver impairment: severe, 10 mg every other day.

• East Africa: low cost and widely available, and rarely sedating.

Formulations. Tablets 10 mg, syrup 5 mg/5 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 kidney or liver impairment. Therapeutic drug monitoring is not used.

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