What is the standard adult Diphenhydramine dose given IV/IO?

• A. 50 mg IV/IO
• B. 25 mg IV/IO
• C. 25 mg IM
• D. 50 mg IM

Answer: (B)

Dosing depends on the route of administration. For diphenhydramine in adults, giving it by IV or IO uses a lower dose to achieve rapid antihistamine effect while minimizing risks like hypotension, excessive sedation, or cardiac effects that can come with a faster IV push.

Diphenhydramine blocks H1 receptors to alleviate histamine-driven symptoms. When given IV/IO, the drug acts quickly, so a 25 mg dose is chosen to provide effectiveness without overshooting into adverse effects. In contrast, the intramuscular route typically uses a higher dose (commonly 50 mg) because absorption is slower and peak levels are lower, requiring a larger amount to achieve similar effect.

So, the standard adult dose for IV/IO administration is 25 mg, reflecting the balance between rapid onset and safety for this route.