Drug General Information (ID: DDIEGY3OWZ)
Drug Name			Diphenhydramine		Drug Info		Histamine		Drug Info
Drug Type		Small molecule				Small molecule
Therapeutic Class		Antiallergic Agents				Antiallergic Agents
Structure

Mechanism of Diphenhydramine-Histamine Interaction (Severity Level: Moderate)
Attenuated pharmacological effects (Unspecific) Click to Show/Hide Mechanism Graph
Drug Name		Diphenhydramine				Histamine
Mechanism		Inhibition of response to histamine phosphate				Histamine
Key Mechanism Factor 1
		Factor Name		Pharmacodynamics
		Factor Description		Reduced pharmacological effects leading to insufficient efficacy and/or treatment failure.
Mechanism Description		Attenuated pharmacological effects of  Histamine when combined with Diphenhydramine

Recommended Action
Management		Clinicians should be aware of the potential for falsely insignificant or false-negative results when administering histamine phosphate to patients treated with antihistamines.

References
1	Product Information. Fycompa (perampanel). Eisai Inc, Teaneck, NJ.
2	Warrington SJ, Ankier SI, Turner P "Evaluation of possible interactions between ethanol and trazodone or amitriptyline." Neuropsychobiology 15 (1986): 31-7. [PMID: 3725002]
3	Product Information. Histatrol (histamine phosphate). Center Laboratories, Port Washington, NY.