Diphenhydramine for sedation emergencies covers one situation: an allergic reaction during moderate sedation, from mild itching and hives up to more serious involvement. Given by injection, it blocks the histamine response causing the reaction.
Dosage:
Initial dose: 25-50 mg up to 100 mg if required
Onset of action: 2-3 minutes
Peak effect: 60-90 minutes
Duration of effect: More than 240 minutes
Reversal Agent
None
Diphenhydramine in Moderate Sedation
Diphenhydramine is kept on hand for an allergic reaction that develops during moderate sedation, not given as a routine part of the sedation itself. Once given, watch the patient for the reaction settling — hives fading, itching easing, any airway involvement resolving — over the next 60 to 90 minutes as the drug reaches peak effect. Because diphenhydramine itself causes drowsiness, a patient who received it during a sedation case needs the same recovery criteria applied a little more conservatively, since the drug’s own sedating effect can be hard to separate from the sedation medications already on board. There is no reversal agent for diphenhydramine; recovery is monitored, not reversed. As with any medication given during moderate sedation, administration follows the facility’s sedation policy and the provider’s scope of practice.
Educational reference for sedation providers, relocated from the previous version of this site — not a substitute for the current package insert, your facility protocols, or clinical judgment. Verify all doses against current references before clinical use.