What are the appropriate dosing regimens of fexofenadine and bilastine for chronic urticaria in adults and children, and how should the doses be adjusted in patients with renal impairment?

Dosing of Fexofenadine and Bilastine in Urticaria

For chronic urticaria, start with fexofenadine 180 mg once daily or 60 mg twice daily in adults, and bilastine 20 mg once daily in adults/adolescents ≥12 years; if inadequate control after 2-4 weeks, increase up to 4-fold the standard dose before considering other therapies.

Standard Dosing Regimens

Fexofenadine

Adults and children ≥12 years:

• Standard dose: 60 mg twice daily OR 180 mg once daily 1
• In renal impairment: Start with 60 mg once daily 1

Children 6-11 years:

• Standard dose: 30 mg twice daily 1
• In renal impairment: Start with 30 mg once daily 1

Bilastine

Adults and adolescents ≥12 years:

• Standard dose: 20 mg once daily 2
• No dose adjustment needed in renal or hepatic impairment 2

Children 6 to <12 years:

• Standard dose: 10 mg once daily 2, 3
• Available as oral solution or orodispersible tablet 3

Up-Dosing Strategy for Inadequate Control

The 2022 international urticaria guidelines establish a clear algorithmic approach 4:

Step 1: Begin with standard-dose second-generation antihistamine

Step 2: If inadequate control after 2-4 weeks (or earlier if symptoms are intolerable):

• Increase dose up to 4-fold the standard dose 4

Evidence-Based Up-Dosing Recommendations

Fexofenadine:

• Can be safely increased to 3-fold standard dose (up to 540 mg daily in adults) 5
• Grade A recommendation for up-dosing 5
• No dose-dependent increase in adverse effects 5

Bilastine:

• Can be safely increased to 4-fold standard dose (80 mg once daily in adults) 6, 5, 7
• Grade A recommendation for up-dosing 5
• Superior efficacy at 2-fold dosing compared to combination therapy with first-generation antihistamines 7
• Significantly lower somnolence compared to levocetirizine 7
• No cardiotoxicity even at supratherapeutic doses 6

Special Populations

Renal Impairment

• Fexofenadine: Reduce starting dose by 50% (60 mg once daily in adults, 30 mg once daily in children 6-11 years) 1
• Bilastine: No dose adjustment required 2

Hepatic Impairment

• Fexofenadine: No specific guidance in label, but minimal hepatic metabolism suggests safety 1
• Bilastine: No dose adjustment required; not significantly metabolized 2, 6

Elderly

• Bilastine: No dose adjustment required 2

Step-Down Protocol

Once complete disease control is achieved (UCT score >16):

• Maintain complete control for at least 3 consecutive months before attempting step-down 4
• Reduce dose by no more than 1 tablet per month 4
• If breakthrough symptoms occur, return to the last dose that provided complete control 4

Key Clinical Considerations

Drug interactions:

• Bilastine has minimal drug-drug interaction potential as it doesn't interact with CYP450 system 2, 6
• Fexofenadine is not significantly metabolized, limiting interactions 8

Sedation risk:

• Both agents are non-sedating at standard doses 2, 8
• Bilastine demonstrates significantly lower somnolence even at higher doses compared to other antihistamines 7

Pediatric data:

• Limited up-dosing data exists for children; only cetirizine and rupatadine have documented pediatric up-dosing safety 5
• Standard dosing is well-established for both agents in children ≥6 years 1, 2, 3

Common Pitfalls to Avoid

• Don't combine antihistamines before attempting up-dosing to 4-fold; up-dosing is more effective and better tolerated than combination therapy 7
• Don't step down prematurely; wait for 3 months of complete control to assess for spontaneous remission 4
• Don't forget renal adjustment for fexofenadine in patients with decreased renal function 1