What treatment is recommended for a 9-month-old baby, weighing 10.5 kg, with a cat allergy, who develops hives upon exposure to cats?

Treatment Recommendation for 9-Month-Old with Cat Allergy and Hives

For this 9-month-old infant with cat-induced hives, use cetirizine alone as first-line treatment; the addition of famotidine (an H2 antihistamine) is not supported by evidence for simple urticaria and should be reserved only for severe anaphylactic reactions where it serves as adjunctive therapy after epinephrine. 1, 2

Why Cetirizine Alone is Appropriate

• Oral H1 antihistamines like cetirizine are the first-line treatment for non-anaphylactic allergic reactions presenting with hives or rash in children. 1
• Second-generation antihistamines (cetirizine, loratadine) are preferred over first-generation options because they cause less sedation and performance impairment in children. 3
• For episodic allergic reactions like hives from cat exposure, antihistamines can be used on an as-needed (PRN) basis due to their relatively rapid onset of action. 3

Why Famotidine Should NOT Be Added

• H2 antihistamines like famotidine have minimal evidence supporting their use in simple allergic reactions and should not be substituted for or routinely added to first-line H1 antihistamine treatment. 2
• The combination of H1 and H2 antihistamines is recommended specifically for anaphylaxis as adjunctive therapy after epinephrine, not for isolated hives. 3, 2
• Using H2 blockers inappropriately may create a false sense of adequate treatment and delay recognition of more serious reactions. 2

Proper Treatment Algorithm

For Simple Hives (Current Scenario)

• Administer cetirizine at weight-appropriate dosing when the baby develops hives after cat contact. 1
• Monitor for progression of symptoms to other organ systems (respiratory, gastrointestinal, cardiovascular). 1
• If symptoms are limited to skin (hives, rash, localized itching) without systemic involvement, continue with H1 antihistamine alone. 1

If Reaction Progresses to Anaphylaxis

• Epinephrine is the ONLY first-line treatment for anaphylaxis - administer immediately if the baby develops diffuse hives, respiratory symptoms (wheezing, stridor, difficulty breathing), obstructive swelling of tongue/lips, or circulatory symptoms. 2
• Only after epinephrine administration should H1 antihistamines, H2 antihistamines (famotidine), and corticosteroids be given as adjunctive therapy. 2
• The importance of co-administering both H1 and H2 antihistamines in anaphylaxis is to prevent severe cardiac deficit. 3

Critical Pitfalls to Avoid

• Never use antihistamines (H1 or H2) as primary treatment for anaphylaxis - this is the most common reason for failure to use epinephrine and significantly increases risk of life-threatening progression. 2
• Do not delay epinephrine administration to give antihistamines if signs of anaphylaxis are present. 2
• Distinguish between non-anaphylactic reactions (isolated hives) and true anaphylaxis, which requires immediate epinephrine. 1

Environmental Control Measures (Essential)

Since the baby lives with cats, implement these measures to reduce allergen exposure:

• Avoidance is the most effective management strategy - strongly consider removing the cat from the home. 3
• If removal is not possible, confine the cat to an uncarpeted room (not the baby's bedroom) with HEPA filtration, which can reduce airborne allergen dissemination by 90%. 3
• Cat allergen can persist for an average of 20 weeks after cat removal, so symptoms may continue even after the cat is gone. 3, 4
• Wash the cat weekly to reduce airborne allergen levels. 3
• Use HEPA air filtration in the home, which has increasing evidence for effectiveness in reducing cat allergen exposure. 3
• Keep the cat out of the baby's bedroom at all times. 1

When to Escalate Care

• If hives persist or worsen despite antihistamine treatment, refer to an allergist/immunologist. 1
• Prescribe an epinephrine auto-injector if the baby has ever had or develops signs of anaphylaxis (respiratory symptoms, cardiovascular symptoms, or multi-system involvement). 3, 1
• All food-allergic patients and those with severe allergic reactions should be prescribed epinephrine autoinjectors. 3

Follow-Up Considerations

• For recurrent reactions despite environmental control, referral to an allergist is warranted for comprehensive evaluation. 1
• Allergen immunotherapy is typically not initiated in children under 5 years unless benefits clearly outweigh risks. 1
• The prevalence of cat allergy increases with age, and children are more often allergic to cats than dogs due to increased intimacy of exposure. 5