Levocetirizine

Levocetirizine is the active R-enantiomer of cetirizine, used for allergic rhinitis and chronic urticaria at half the cetirizine dose. It is less sedating than cetirizine but can still cause drowsiness. It does not treat anaphylaxis.

Classification. Second-generation H1 antihistamine.

Mechanism. Selective peripheral H1 receptor antagonist with higher receptor affinity than the racemate.

Pharmacokinetics. Onset within 1 hour, duration 24 hours. Bioavailability over 85%. Minimal metabolism. Half-life about 8 hours. About 85% is excreted unchanged in urine.

First-line, allergic rhinitis and urticaria, adults and children from 12 years. 5 mg once daily. In some regions 2.5 mg once daily is the starting dose.

Children. 6 to 11 years: 5 mg once daily in most regions; 2.5 mg once daily in others. 2 to 5 years: 1.25 mg twice daily or once daily by region. 6 months to 2 years, where licensed: 1.25 mg once daily.

Specialist, chronic spontaneous urticaria not controlled at the usual dose. Up to 4 times the usual dose (20 mg daily) under specialist direction.

Emergency. Not used.

Titration and loading. None.

Contraindications. Hypersensitivity to levocetirizine, cetirizine or hydroxyzine. Kidney failure with GFR under 10 mL/min or dialysis.

Serious adverse effects. Withdrawal pruritus after prolonged use, angioedema, urinary retention, seizures at overdose.

Common adverse effects. Drowsiness, dry mouth, fatigue, headache.

Interactions. Alcohol and sedatives add drowsiness. Theophylline slightly lowers clearance.

Common prescribing errors. Not adjusting for kidney function. Using in the evening before driving. Doubling with cetirizine.

Special groups.

• Pregnancy: limited data; loratadine or cetirizine are preferred. Breastfeeding: excreted into milk; avoid.

• Older adults: adjust for kidney function.

• Kidney impairment (5 mg adult dose): GFR 50 to 80 mL/min, 5 mg once daily; 30 to 49 mL/min, 5 mg every 2 days; 10 to 29 mL/min, 5 mg every 3 days; under 10 mL/min, avoid. Liver impairment: no adjustment unless kidney function is also reduced.

• East Africa: low cost and widely sold. Warn about drowsiness.

Formulations. Tablets 5 mg, oral solution 2.5 mg/5 mL.

Administration. Once daily in the evening, with or without food.

Baseline. Urticaria activity score, kidney function in older adults and those at risk.

Monitoring. Symptoms, sedation, urinary symptoms. Review at 2 to 4 weeks.

Stop and reduce rules. Lengthen the interval in kidney impairment. Taper if itching appears after long use. Therapeutic drug monitoring is not used.

Referral and escalation. Refer for urticaria not controlled at 4 times the usual dose, or angioedema.