For a 4-month-old infant, cetirizine (Alerid) is generally not recommended without direct medical supervision. The safety and appropriate dosage for infants under 6 months have not been well established.

• Consult a pediatrician: It is very important to speak with your child's doctor before giving any antihistamines or cold medications.

• Cold management: For infants, supportive care such as keeping them hydrated, using a humidifier, and gentle nasal suctioning is usually advised.

• Dosage and frequency: If a pediatrician prescribes cetirizine, they will provide the exact dosage and frequency based on the infant's weight and condition.

Please avoid administering cetirizine or any medication without professional guidance in this age group to ensure safety and proper care.