FIELD REFERENCE
Full criteria & treatment guidance
Indications
- Allergic reaction, dystonic medication reaction, or anaphylaxis after epinephrine under the appropriate OCEMS order.
Contraindications & local exclusions
- The cited injectable label excludes neonates/premature infants, nursing mothers, hypersensitivity to diphenhydramine or chemically similar antihistamines, and use as a local anesthetic. These injectable-label restrictions are separate from OTC oral formulations.
Precautions
- Sedation, hypotension and paradoxical pediatric excitation may occur. Narrow-angle glaucoma and obstructive urinary/GI disease require caution. Diphenhydramine does not replace epinephrine in anaphylaxis.
- These are selected safety checks, not a complete prescribing monograph. Product labeling and OCEMS authorization answer different questions; confirm the actual product, patient population and applicable order.
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.
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
- SO-P-060 pediatric dose: 1 mg/kg 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.
UNDERSTAND THE CARE
Why prior medication changes the next step
The allergic-reaction orders explicitly account for diphenhydramine taken before EMS arrival. Ask for the product, amount and time, including an OTC product the patient may not call by the generic name. Rash-only, angioedema and systemic anaphylaxis are separate branches.
Applying the guidance
For anaphylaxis, initial epinephrine and support of airway, breathing and circulation remain the priorities. The pediatric dose and permitted routes come from the particular allergy or extrapyramidal-reaction order. After treatment, document the symptom response and continue assessment of breathing, perfusion and consciousness rather than focusing on the rash alone.
Dose, concentration and volume
Diagram text & teaching checkpoints
- Indication
- Allergy branch or extrapyramidal reaction.
- Prior dose
- Identify prearrival antihistamine use.
- Sequence
- Epinephrine first in anaphylaxis.
- Response
- Symptoms plus airway, breathing and circulation.
Sources for this explanation
Original OCMedic teaching synthesis of the references below. Educational expansion updated ; this is not a new independent clinical-review date. Source-specific dates and limitations remain in the full guidance.
- I-15 — Adult / Adolescent Standing Order Drug Guide
- I-20 — Pediatric Medication Volume Dose by Weight
- SO-M-015 — Allergic Reaction / Anaphylaxis
- SO-P-060 — Allergic Reaction / Anaphylaxis - Pediatric
- SO-M-050 — Substance Overdose / Poisoning - Adult / Adolescent
- SO-P-085 — Substance Overdose / Poisoning - Pediatric
- Product label — DIPHENHYDRAMINE- diphenhydramine hydrochloride injection, solution
- Name / formulation reference — Medication name and formulation terminology
When the rash improves but the patient does not
A useful reassessment question is whether breathing and circulation have improved, not simply whether the rash is fading. The OCEMS allergy order separates stable skin-only symptoms, facial or cervical angioedema, and anaphylaxis. A change in one symptom does not erase findings that placed the patient in the more urgent branch.
For example, a patient reports taking an OTC antihistamine before the crew arrives and still has wheezing and poor perfusion. Identify the product and time, preserve the order’s prearrival diphenhydramine restriction, and follow the anaphylaxis sequence. Do not make an additional antihistamine the next step merely because it is familiar or readily available.
At handoff, distinguish the prior self-treatment from medication delivered by EMS. Describe airway findings, respiratory effort, perfusion and consciousness before and after care. The dystonic-reaction indication is a separate pathway; an allergy dose table should not be used as the explanation for every diphenhydramine administration.
Source: Allergic Reaction / Anaphylaxis.