Diphenhydramine (Benadryl) is an antihistamine that has a sedative effect in many people. However, some patients may become excited after taking the drug.
Criteria:
(1) agitation, excitation or psychiatric symptoms following ingestion of diphenhydramine
(2) exclusion of other causes (mental illness, stimulant overdose, etc).
The severity of the response increases with dose or with parenteral administration.
De Leon et al associated paradoxical excitation with CYP2D6 ultrarapid metabolizers, who are patients with 3 or more active copies of the CYP2D6 gene. In addition to atypical reactions to diphenhydramine, these patients may have atypical reactions to:
(1) oxycodone or hydrocodone (results in opioid intoxication)
(2) tricyclic antidepressants (results in rapid metabolism with poor response)
(3) antipsychotic medication (results in rapid metabolism with poor response)
To read more or access our algorithms and calculators, please log in or register.
