Check before giving

The allergy standing orders say not to give another dose if diphenhydramine was taken before arrival.
A rash-only stable reaction has a different pathway from facial/cervical angioedema or anaphylaxis; assess the full presentation.

Use in OCEMS

Used in specified allergic/angioedema pathways and medication-induced extrapyramidal reactions.
For anaphylaxis, epinephrine is given first. Diphenhydramine does not replace treatment of airway compromise or shock.

Indication / route	Dose & limits
Allergic reaction / dystonic reaction	50 mg IM or IV once.
IO use in I-15	Only when an IO is already established for fluid administration.

SO-P-060 allergic/anaphylactic pathway: 1 mg/kg IM/IV/IO once, maximum 50 mg.
SO-P-085 extrapyramidal reaction: 1 mg/kg IM/IV, maximum 50 mg, once; consult the complete order for IO provisions.

Source: SO-P-060. Dose rule: 1 mg/kg; route: IM/IV/IO.
1 mg/kg IM/IV/IO once; maximum 50 mg. Use the anaphylaxis pathway when indicated; diphenhydramine does not replace epinephrine.
Do not administer another dose if diphenhydramine was taken before EMS arrival under SO-P-060.
SO-P-085 uses the same 1 mg/kg, maximum 50 mg, for extrapyramidal reactions, with its own route provisions.
Calculated examples for the exact weights shown, using the named standing-order/procedure formula. Do not round the patient’s weight to the nearest row. For another weight, calculate from the stated formula and apply the limits. These are not the rounded I-20 weight-band volumes.
Volumes are mathematical examples rounded to at most three decimal places. Verify the vial concentration, dose, and measurable syringe volume before administration; follow agency preparation/rounding practice.

The inventory preparation is 50 mg/mL. Use patient weight and the maximum dose when calculating pediatric volume.
Reassess airway, respiratory effort, perfusion, and mental status. Document prior self-treatment and the response.