AHFS Class:

4:04 First Generation Antihistamines

Generic Name

• DiphenhydrAMINE Hydrochloride

Diphenhydramine hydrochloride is available as a 50-mg/mL solution in 1- and 10-mL vials.³⁷³⁰; ³⁷³¹ Each mL of diphenhydramine hydrochloride solution also contains 0.1 mg of benzethonium chloride.³⁷³⁰; ³⁷³¹ The pH may have been adjusted with sodium hydroxide and/or hydrochloric acid.³⁷³⁰; ³⁷³¹

Diphenhydramine hydrochloride also is available as a 50-mg/mL solution in 1-mL single-use (preservative-free) vials, ampuls, and prefilled syringes.³⁷³²; ³⁷³³ The pH may have been adjusted with sodium hydroxide or hydrochloric acid.³⁷³²; ³⁷³³

pH

From 4 to 6.5.³⁷³⁰; ³⁷³¹; ³⁷³²; ³⁷³³ A narrower pH range of 5 to 6 has been stated by a manufacturer (Mylan).³⁷³¹

Trade Name(s)

Benadryl

Diphenhydramine hydrochloride is administered by deep intramuscular injection, slow direct intravenous injection, or continuous or intermittent intravenous infusion.⁴; ³⁷³⁰; ³⁷³¹; ³⁷³²; ³⁷³³ Manufacturers state that the rate of intravenous administration generally should not exceed 25 mg/min.³⁷³⁰; ³⁷³¹; ³⁷³²; ³⁷³³ Subcutaneous or perivascular injection should be avoided due to irritation.⁴ Local necrosis has been associated with subcutaneous or intradermal administration.³⁷³⁰

Intact containers of diphenhydramine hydrochloride should be stored at controlled room temperature and protected from light.³⁷³⁰; ³⁷³¹; ³⁷³²; ³⁷³³ Freezing should be avoided.³⁷³¹; ³⁷³²; ³⁷³³

Diphenhydramine hydrochloride under simulated summer conditions in paramedic vehicles was exposed to temperatures ranging from 26 to 38°C over 4 weeks. Analysis found no loss of the drug under these conditions.²⁵⁶²

Central Venous Catheter

Diphenhydramine hydrochloride (Schein) 2 mg/mL in dextrose 5% was found to be compatible with the ARROWg+ard Blue Plus (Arrow International) chlorhexidine-bearing triple-lumen central catheter. Essentially complete delivery of the drug was found with little or no drug loss occurring. Furthermore, chlorhexidine delivered from the catheter remained at trace amounts with no substantial increase due to the delivery of the drug through the catheter.²³³⁵

Solution Compatibility

Additive Compatibility

Drugs in Syringe Compatibility

Y-Site Injection Compatibility (1:1 Mixture)

For a list of references cited in the text of this monograph, search the monograph titled References.

ASHP^® Injectable Drug Information^TM. Selected Revisions March 31, 2024. © Copyright, 2024. American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.