What are the appropriate IV doses of Benadryl (diphenhydramine), Famotidine, and Solu-Medrol (methylprednisolone) for a 28kg, 5-year-old child presenting with an allergic reaction characterized by hives and facial swelling?

Appropriate IV Medication Dosing for a 28kg Child with Allergic Reaction

Critical Safety Consideration First

While you plan to administer adjunctive medications, this presentation of hives with facial swelling warrants serious consideration for IM epinephrine, as facial swelling may represent angioedema and potential airway involvement—a criterion for anaphylaxis treatment. 1

Specific Dosing for This 28kg Child

Diphenhydramine (Benadryl) IV

• Dose: 28-56 mg IV (1-2 mg/kg per dose) 1
• Maximum: 50 mg per dose 1, 2
• For this 28kg child: Give 28 mg IV (using the lower end of the range) to stay well below the 50 mg maximum 1
• Critical safety warning: Administer slowly over several minutes, NOT as rapid IV push 3, 4
  • Rapid IV administration has been associated with cardiac arrest in pediatric patients, even at therapeutic doses 3
  • Cardiovascular effects including hypotension and arrhythmias are more common with IV route 3, 4

Famotidine (H2-Blocker) IV

• Dose: 7 mg IV (0.25 mg/kg) 5
• Maximum: 40 mg/day 5
• Administration: Inject over at least 2 minutes OR as a 15-minute infusion 5
• Frequency: Every 12 hours 5
• Note: The guidelines reference ranitidine (1 mg/kg), but since famotidine is now the standard H2-blocker, use 0.25 mg/kg per FDA labeling 1, 5

Methylprednisolone (Solu-Medrol) IV

• Dose: 28 mg IV (1 mg/kg) 1
• Maximum: 60-80 mg 1
• Administration: Can be given IV push over several minutes or as infusion 6
• The guideline range is 1-2 mg/kg/day, but 1 mg/kg is standard for acute allergic reactions 1

Clinical Algorithm for Decision-Making

Reassess for Anaphylaxis Criteria Before Proceeding

You must evaluate for any of the following, which would mandate IM epinephrine FIRST: 1

• Respiratory involvement: wheezing, stridor, dyspnea, hypoxemia
• Cardiovascular involvement: hypotension, tachycardia, dizziness, syncope
• Persistent gastrointestinal symptoms: vomiting, cramping abdominal pain
• Rapidly progressive symptoms

If ANY of these are present, give IM epinephrine 0.3 mg (0.01 mg/kg) in the anterolateral thigh IMMEDIATELY before adjunctive medications 1

If Truly Isolated Cutaneous Reaction

• Proceed with the adjunctive medication regimen outlined above 1
• The combination of H1-antihistamine (diphenhydramine) plus H2-antihistamine (famotidine) is superior to H1-antihistamine alone for urticaria control 1
• Corticosteroids may help prevent biphasic reactions, though their acute benefit is limited 1

Critical Pitfalls to Avoid

Diphenhydramine Administration Errors

• Never give diphenhydramine as rapid IV push 3, 4
• Consider using oral liquid formulation instead of IV when possible, as it absorbs rapidly and avoids cardiovascular risks 1, 2
• Be aware that sedation may mask progression of symptoms 2, 4

Underestimating Severity

• Facial swelling can progress to airway compromise 1
• Have IM epinephrine immediately available at bedside 1
• Monitor continuously for at least 4-6 hours for biphasic reactions 1

Observation Period

• Observe for minimum 4-6 hours after symptom resolution 1
• Biphasic reactions occur in a subset of patients and can be severe 1
• Longer observation warranted if symptoms were severe or required multiple interventions 1

Discharge Planning (If Applicable)

• Prescribe epinephrine auto-injector (0.3 mg for >25 kg) 1
• Continue oral antihistamines for 2-3 days 1
• Consider oral prednisone 1 mg/kg daily for 2-3 days 1
• Arrange allergy/immunology follow-up 1