Cetirizine (Zyrtec) Dosing for 6-Month-Old Infants
Cetirizine is not FDA-approved for infants under 6 months of age, and there are no established dosing recommendations for this age group in standard guidelines or drug labeling.
Critical Safety Considerations
No approved dosing exists for infants younger than 6 months in FDA labeling or major pediatric guidelines 1, 2, 3
The only safety data available for cetirizine in young infants comes from a single study in infants aged 6-11 months, which used 0.25 mg/kg twice daily (mean daily dose 4.5 mg) 4
This study demonstrated safety over one week but was specifically conducted in infants 6 months and older, not younger 4
Why This Matters for a 6-Month-Old
At exactly 6 months of age, your patient falls at the absolute lower boundary of studied populations 4
The tolerability profile in infants 6-24 months was similar to placebo in available studies, with cetirizine potentially causing less sleep disturbance than placebo 2, 4
Cetirizine may cause mild sedation (13.7% in older patients), though this was not prominent in the infant study 1, 4
Practical Recommendation
If cetirizine must be used in a 6-month-old infant, the only evidence-based approach is 0.25 mg/kg administered twice daily, based on the single safety study in this age range 4. This translates to approximately:
2-2.5 mg twice daily for an average 8-10 kg infant 4
This should only be used after consultation with the infant's pediatrician, as this represents off-label use at the youngest studied age 4, 3
Important Caveats
Alternative management strategies for allergic conditions should be strongly considered first 2, 3
The study demonstrating safety was only 7 days in duration 4
Third-generation antihistamines like cetirizine have improved safety profiles compared to older agents, but data in infants under 1 year remain limited 3