What is the recommended per kilogram dose of diphenhydramine (antihistamine) in neonates?

Diphenhydramine Dosing in Neonates

The American Academy of Pediatrics does not provide specific dosing recommendations for diphenhydramine in neonates, indicating caution should be exercised when considering its use in this population. 1

Dosing Considerations

• Pediatric guidelines mention diphenhydramine for acute hypersensitivity reactions and dystonic reactions at 1-2 mg/kg IV/IM (maximum 50 mg), but these recommendations are not specific to neonates 2, 1
• Neonates are particularly vulnerable to adverse effects of antihistamines due to their immature metabolic pathways and blood-brain barrier 1, 3
• Rapid IV administration of diphenhydramine should be avoided in neonates as it may precipitate seizures 1

Clinical Approach to Allergic Reactions in Neonates

• For allergic reactions in neonates requiring intervention:
  • Epinephrine remains the first-line treatment for severe allergic reactions, with appropriate neonatal dosing (0.01-0.03 mg/kg of 1:10,000 solution) 1
  • Consultation with a pediatric allergist or emergency medicine specialist is strongly recommended before administering any antihistamine 1

Safety Concerns

• Diphenhydramine can cause significant adverse effects in neonates, including:
  • Sedation and respiratory suppression (especially if used with other sedative agents) 2
  • Hypotension 2
  • Paradoxical excitement or agitation 2
  • Seizures (particularly with rapid IV administration) 1

Emergency Situations

• If diphenhydramine must be used in emergency situations for severe allergic reactions when no alternatives exist:
  • Administer with extreme caution 1
  • Monitor closely for respiratory depression, hypotension, and neurological effects 2, 4
  • Consider lower doses than those used in older infants due to immature metabolic pathways in neonates 5

Alternative Approaches

• Second-generation antihistamines have fewer adverse effects because they are more selective for peripheral H1 receptors, but most lack specific dosing guidelines for neonates 3
• Many antihistamines are prescribed off-label in children younger than 2 years of age, where safety data are most lacking 3

Toxicity Considerations

• For suspected diphenhydramine overdose in children under 6 years, a threshold of 7.5 mg/kg warrants emergency department referral 6
• Symptoms of toxicity include changes in behavior beyond mild drowsiness, agitation, hallucinations, abnormal muscle movements, loss of consciousness, seizures, or respiratory depression 6