# Diphenhydramine (Benadryl)

Allergic and dystonic reactions: weight-based pediatric dosing and adjunctive use in anaphylaxis.

Population: Adult & pediatric guidance. Scope: ALS.
Status: published. Source-linked OCEMS summary.
Summary updated: 2026-09-16.
Source checked: 2026-09-16.
Source version: I-15 revised March 31, 2026; I-20 revised March 26, 2026. Both implemented April 1, 2026. See linked condition-specific sources..
Canonical page: https://www.ocmedic.com/guides/diphenhydramine/
Official source: [I-15 — Adult / Adolescent Standing Order Drug Guide](https://www.ochealthinfo.com/sites/healthcare/files/2026-04/I-15%20Adult%20SO%20Drug%20Guide%2004-2026.pdf)

Independent OC Medic summary. Does not replace the complete policy, current system notices, or clinical judgment.

## 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.

## Source documents

- [I-15 — Adult / Adolescent Standing Order Drug Guide](https://www.ochealthinfo.com/sites/healthcare/files/2026-04/I-15%20Adult%20SO%20Drug%20Guide%2004-2026.pdf#page=1)
- [I-20 — Pediatric Medication Volume Dose by Weight](https://www.ochealthinfo.com/sites/healthcare/files/2026-04/I-20%20Peds%20Drug%20Guide%2004-2026.pdf)
- [SO-M-015 — Allergic Reaction / Anaphylaxis](https://www.ochealthinfo.com/sites/healthcare/files/2023-04/SO-M-15%20Allergic%20Rxn%204-2023.pdf)
- [SO-P-060 — Allergic Reaction / Anaphylaxis - Pediatric](https://www.ochealthinfo.com/sites/healthcare/files/2023-04/SO-P-60%20Allergic%20Rxn%204-2023.pdf)
- [SO-M-050 — Substance Overdose / Poisoning - Adult / Adolescent](https://www.ochealthinfo.com/sites/hca/files/2021-10/SO-M-50%20Poisoning%20OD.pdf)
- [SO-P-085 — Substance Overdose / Poisoning - Pediatric](https://www.ochealthinfo.com/sites/healthcare/files/2023-09/SO-P-85%20OD%2010-2023.pdf)

## 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.

## Adult / adolescent

| 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. |

## Pediatric

- 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.

## Pediatric weight table — Allergic reaction / anaphylaxis

- 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.
| Exact weight | Dose — IM/IV/IO | Volume at 50 mg/mL |
| --- | --- | --- |
| 3 kg | 3 mg | 0.06 mL |
| 4 kg | 4 mg | 0.08 mL |
| 5 kg | 5 mg | 0.1 mL |
| 6 kg | 6 mg | 0.12 mL |
| 8 kg | 8 mg | 0.16 mL |
| 10 kg | 10 mg | 0.2 mL |
| 12 kg | 12 mg | 0.24 mL |
| 15 kg | 15 mg | 0.3 mL |
| 20 kg | 20 mg | 0.4 mL |
| 25 kg | 25 mg | 0.5 mL |
| 30 kg | 30 mg | 0.6 mL |
| 35 kg | 35 mg | 0.7 mL |
| 40 kg | 40 mg | 0.8 mL |
| 45 kg | 45 mg | 0.9 mL |
| 50 kg | 50 mg | 1 mL |
| 60 kg | 50 mg | 1 mL |

## Preparation & reassessment

- 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.