What are the daily doses of cetirizine and famotidine for a 9-month-old, 10.5 kg infant with allergies (allergic reactions) to cats and gastroesophageal reflux disease (GERD)?

Dosing Recommendations for a 9-Month-Old, 10.5 kg Infant

Cetirizine Dosing

For this 9-month-old, 10.5 kg infant with cat allergies, cetirizine is not recommended as it is only FDA-approved for children ≥6 months for chronic urticaria, not for environmental allergies at this age. However, if used off-label for allergic symptoms, the typical dose would be 2.5 mg once daily based on weight-based dosing extrapolated from older pediatric data 1.

Key Considerations for Cetirizine:

• Age limitation: Standard cetirizine dosing guidelines do not provide specific recommendations for infants under 12 months for allergic rhinitis 1
• Off-label use: If prescribed off-label by an allergist, the dose is typically 0.25 mg/kg/day, which equals approximately 2.5 mg once daily for this 10.5 kg infant
• Formulation: Available as oral solution (1 mg/mL or 5 mg/5 mL), making 2.5 mL of the 1 mg/mL solution the practical dose
• Timing: Once daily dosing, preferably in the evening due to potential mild sedation

Important Caveats:

• Environmental allergy management in infants primarily focuses on allergen avoidance rather than pharmacotherapy
• Antihistamines should be reserved for acute allergic reactions with urticaria or other immediate symptoms 1
• Consider allergist referral for comprehensive evaluation before initiating chronic antihistamine therapy in an infant

Famotidine Dosing

For reflux symptoms in this 10.5 kg infant, famotidine 1-2 mg/kg/day divided into 2-3 doses is the appropriate regimen, which translates to 10.5-21 mg total daily dose, practically given as 5-10 mg twice daily. 2

Specific Dosing Protocol:

• Starting dose: 5 mg twice daily (approximately 1 mg/kg/day total) 2
• Maximum dose: 10 mg twice daily (approximately 2 mg/kg/day total) if needed for symptom control 2
• Frequency: Twice daily for infants >10 kg; three times daily may be used for infants <10 kg 2
• Route: Oral suspension preferred; IV formulation available if needed initially 2

Practical Prescribing:

• Formulation: Famotidine oral suspension 40 mg/5 mL (8 mg/mL)
• Volume per dose: 0.6-1.25 mL per dose for 5-10 mg dosing
• Administration: Give 30-60 minutes before meals when possible
• Duration: Expect improvement within 7 days, with significant reduction in symptoms by 2-3 weeks 2

Evidence-Based Efficacy:

• In severely handicapped children with reflux esophagitis, famotidine at 1-2 mg/kg/day showed marked or moderate effectiveness in 70% of cases, with 94% showing improvement within three weeks 2
• No significant side effects were observed in pediatric studies at these doses 2
• Transient mild liver enzyme elevations may occur but are typically not clinically significant 2

Critical Safety Points:

• Monitor for: Diarrhea and urticaria (rare side effects reported at higher doses) 3
• Dose reduction: Consider if side effects develop, reducing to once daily dosing 3
• Alternative consideration: Proton pump inhibitors (omeprazole 0.7-1.4 mg/kg/day) may be more effective for severe or refractory GERD, though famotidine is reasonable first-line therapy 4

When to Escalate Therapy:

• If symptoms persist after 4 weeks of famotidine at maximum dose (2 mg/kg/day), consider switching to omeprazole 0.7 mg/kg/day initially, escalating to 1.4-2.8 mg/kg/day if needed 4
• Persistent symptoms warrant pediatric gastroenterology referral for possible endoscopic evaluation