Is Benadryl (diphenhydramine), haloperidol, and Ativan (lorazepam) compatible when administered together in the same IV line?

IV Compatibility of Diphenhydramine, Haloperidol, and Lorazepam

Diphenhydramine, haloperidol, and lorazepam are physically compatible when administered together in the same IV line and can be safely combined in a single syringe for administration.

Evidence for Compatibility

The most recent and highest quality evidence from a 2023 study specifically evaluated the physical compatibility of various psychotropic medication combinations in syringes. This study confirmed that the triple combination of lorazepam and haloperidol with diphenhydramine is physically compatible 1. The researchers validated this compatibility using both visual inspection and particle counter evaluations according to United States Pharmacopoeia standards.

Additionally, a 2015 study demonstrated that diphenhydramine hydrochloride and lorazepam maintained greater than 95% of their original concentration over 48 hours when combined in solution 2, further supporting their compatibility.

Clinical Applications

This combination is commonly used in several clinical scenarios:

1. Acute agitation management:

   • The combination of a benzodiazepine (lorazepam) and an antipsychotic (haloperidol) is recommended for rapid sedation in acutely agitated patients 3
   • Diphenhydramine is often added to prevent extrapyramidal side effects from haloperidol

2. Antiemetic therapy:

   • This combination (sometimes called "ABH") is used in end-of-life care for nausea and vomiting management 4
   • Lorazepam and diphenhydramine are recognized as useful adjuncts to antiemetic drugs 3

Dosing Considerations

When administering these medications together:

• Haloperidol: Typical dose 0.5-5 mg IV/IM for acute agitation
• Lorazepam: Typical dose 1-2 mg IV/IM for acute agitation
• Diphenhydramine: Typical dose 25-50 mg IV/IM

Administration Guidelines

1. Preparation: These medications can be combined in the same syringe for administration
2. Administration rate: Administer slowly to minimize the risk of hypotension
3. Monitoring: Observe for:
   • Excessive sedation
   • Respiratory depression
   • Hypotension
   • Extrapyramidal symptoms
   • QT prolongation (particularly with haloperidol)

Important Considerations

• While physically compatible, be aware that combining these medications may potentiate sedative effects
• This combination provides synergistic effects for managing agitation, with haloperidol addressing psychosis, lorazepam providing anxiolysis, and diphenhydramine preventing extrapyramidal symptoms
• For patients requiring repeated doses, consider transitioning to oral medications when appropriate

Conclusion

The triple combination of diphenhydramine, haloperidol, and lorazepam is physically compatible for IV administration and can be safely combined in the same syringe. This combination is particularly useful for managing acute agitation and as an antiemetic regimen in specific clinical scenarios.