How to treat a hydroxyzine (antihistamine) reaction?

Treatment of Hydroxyzine Reaction

The treatment of a hydroxyzine reaction should focus on immediate discontinuation of the medication, followed by antihistamine administration (H1 and H2 blockers) and supportive care based on symptom severity, with epinephrine reserved for anaphylactic reactions. 1

Assessment and Initial Management

• Stop hydroxyzine immediately 1
• Maintain IV access if available 1
• Assess ABCs (Airway, Breathing, Circulation) and level of consciousness 1
• Position patient appropriately:
  • Trendelenburg position for hypotension
  • Sitting up for respiratory distress
  • Recovery position if unconscious 1
• Administer oxygen if needed 1
• Call for medical assistance if symptoms are severe 1

Treatment Based on Reaction Severity

Mild Reactions (drowsiness, mild sedation, dry mouth)

• Discontinue hydroxyzine
• Supportive care
• Monitor vital signs 1
• Administer antihistamines:
  • H1 blocker: Diphenhydramine 25-50 mg orally or IV 1
  • Consider adding H2 blocker (ranitidine 50 mg) for better control 1

Moderate-Severe Reactions (significant CNS depression, hypotension)

• IV fluids: Rapid infusion of 1-2 liters normal saline at 5-10 mL/kg in first 5 minutes 1
• Combined H1 and H2 antagonists:
  • Diphenhydramine 1-2 mg/kg (25-50 mg) IV slowly 1
  • Ranitidine 50 mg diluted in 5% dextrose (20 mL total volume) IV over 5 minutes 1
• Corticosteroids: Methylprednisolone 1-2 mg/kg IV every 6 hours 1

Anaphylactic Reactions (rare with hydroxyzine)

• Epinephrine 0.01 mg/kg (1mg/mL dilution, maximum 0.5 mL) IM into lateral thigh 1
• Can repeat epinephrine every 5-15 minutes if needed 1
• If no response to IM epinephrine, consider IV epinephrine 1
• Continue fluid resuscitation and antihistamines as above 1

Special Considerations

QT Prolongation

• ECG monitoring is recommended in cases of hydroxyzine overdose due to risk of QT prolongation and Torsade de Pointes 2
• Avoid epinephrine if possible as hydroxyzine can counteract its pressor action 2

Antimuscarinic Effects

• Hydroxyzine has fewer antimuscarinic effects than other antihistamines like diphenhydramine 3
• Physostigmine may be considered for severe antimuscarinic symptoms but is rarely needed 3, 4

Severe Overdose

• Gastric lavage if recent ingestion and patient not already vomiting 2
• Induce vomiting if not spontaneous and if appropriate 2
• General supportive care with frequent vital sign monitoring 2
• No specific antidote exists 2
• Hemodialysis is generally not effective for hydroxyzine removal 2

Post-Reaction Monitoring

• Monitor vital signs and observe for recurrence of symptoms 1
• For severe reactions, close observation for 24 hours is recommended 1
• Document the reaction thoroughly for future reference 1
• Consider allergy consultation before any rechallenge 1

Prevention of Future Reactions

• Avoid hydroxyzine in patients with previous reactions 5
• Consider alternative non-sedating antihistamines for allergic conditions 5, 6
• If antihistamine therapy is needed, second-generation agents like cetirizine, loratadine, or fexofenadine may be safer alternatives 1, 5

Remember that hydroxyzine reactions are typically dose-dependent and most commonly manifest as CNS depression rather than true allergic reactions 3. Proper management focuses on supportive care and symptom control rather than specific antidotes.