Hydroxyzine Should NEVER Be Given Intravenously
Hydroxyzine is absolutely contraindicated for intravenous administration and must only be given intramuscularly. The FDA drug label explicitly states that hydroxyzine intramuscular solution "should not, under any circumstances, be injected subcutaneously, intra-arterially or intravenously" 1. This is a critical safety issue that can result in severe complications including tissue necrosis, thrombosis, and gangrene.
Approved Route: Intramuscular Only
Hydroxyzine is formulated specifically for IM injection and should be administered deep into a large muscle mass 1.
Clinical Indications and IM Dosing
Adult Dosing (IM Only)
- Acute psychiatric/emotional emergencies (including acute alcoholism): 50-100 mg IM stat, then every 4-6 hours as needed 1
- Nausea and vomiting: 25-100 mg IM 1
- Pre/postoperative adjunctive medication: 25-100 mg IM 1
- Pre/postpartum adjunctive therapy: 25-100 mg IM 1
Pediatric Dosing (IM Only)
- Nausea and vomiting: 0.5 mg/lb (1.1 mg/kg) body weight IM 1
- Pre/postoperative adjunctive medication: 0.5 mg/lb (1.1 mg/kg) body weight IM 1
Role in Anaphylaxis (Second-Line Only)
While hydroxyzine appears in older anaphylaxis guidelines, it is never first-line therapy. The 2005 anaphylaxis guidelines mention diphenhydramine (not hydroxyzine specifically) as second-line therapy at 1-2 mg/kg or 25-50 mg parenterally, but emphasize that H1 antihistamines should never be administered alone and are inferior to epinephrine 2.
For anaphylaxis, the treatment algorithm is:
- Epinephrine IM (0.01 mg/kg of 1:1000, max 0.3-0.5 mg) into anterolateral thigh - repeat every 5 minutes as needed 3
- Position patient supine with legs elevated
- Establish IV access and give normal saline bolus (adults: 1-2L at 5-10 mL/kg in first 5 minutes; children: up to 30 mL/kg in first hour) 2
- Consider H1 antihistamine (diphenhydramine preferred over hydroxyzine) as adjunctive therapy only 2
Critical Safety Warnings
- Contraindicated in prolonged QT interval 1
- Contraindicated in early pregnancy (teratogenic in animal studies) 1
- May cause sedation and respiratory depression, especially when combined with other sedatives 4
- Rapid IV administration can precipitate seizures (though IV route is contraindicated regardless) 4
- May cause paradoxical excitement or agitation 4
Practical Considerations
- Hydroxyzine may be administered without further dilution for IM injection 1
- Patients started on IM therapy should be transitioned to oral therapy when practicable 1
- Dosage should be adjusted according to patient response 1
- The antiemetic efficacy of hydroxyzine 100 mg IM has been shown superior to droperidol 2.5 mg IM in some studies 5
Why Not IV?
The formulation contains excipients and has pH characteristics that make it unsuitable for IV administration, risking severe vascular injury, tissue necrosis, and potentially fatal complications. There is no safe IV formulation of hydroxyzine available.