OCEMS DIPHENHYDRAMINE

Diphenhydramine Overview

• Medication: Diphenhydramine HCL (Brand name: Benadryl)

• Classification: Antihistamine

Effects/Characteristics

• Mechanism of Action:

  • Binds to histamine receptor sites, blocking H1 and H2 receptors.

  • Holds anticholinergic properties, leading to decreased itching, edema, and bronchoconstriction.

  • Possesses anti-dyskinetic properties.

Pharmacokinetics

• Onset: 15-30 minutes

• Peak Effect: 2-3 hours

• Duration: 6-12 hours

Dosage Forms

• Prefilled Syringe: 50 mg/1ml Pre Filled Syringe

• Vial: 50 mg/1ml Vial

Prehospital Routes of Administration

• Routes:

  • Intravenous

  • Intramuscular

  • Intraosseous

Treatment Protocols and Indications

• Allergic Reaction/Anaphylaxis Treatment (Adult):

  • Diphenhydramine 50 mg IM or IV once.

  • Administer only if diphenhydramine has not been taken prior to arrival.

• Substance Overdose/Poisoning (Suspected Extrapyramidal Reaction (Adult)):

  • Diphenhydramine 50 mg IM or IV once.

• Pediatric Dosage for Allergic Reaction/Anaphylaxis (Pediatric):

  • Diphenhydramine (Benadryl) 1mg/Kg Intramuscular/Intravenous/Intraosseous once (maximum dose 50mg). Do not administer if Diphenhydramine taken prior to arrival.

• Pediatric Dosage for Substance Overdose/Poisoning (Pediatric):

  • Diphenhydramine 1 mg/kg IM or IV, max single dose 50 mg, once.

Side Effects

• Common Side Effects:

  • Dry Mouth

  • Drowsiness

  • Palpitations

  • Mild Hypotension

• Critical Notes:

  • Does not prevent histamine release.

  • Potentiates effects of other CNS depressants (e.g., alcohol, sedatives).

Precautions

• Generally, intraosseous (IO) administration should be reserved for patients in anaphylaxis where IO access was already established for epinephrine and fluid administration.

• Epinephrine: Priority medication in anaphylaxis cases.

• Use caution if the patient has a history of asthma or consider withholding the medication.

• Dystonic Reactions:

  • Typically occur 1-2 weeks after starting antipsychotic medications.

  • Medications associated with dystonic reactions include:

    • Thorazine (Chlorpromazine)

    • Taractan (Chlorprothixene)

    • Prolixin (Fluphenazine)

    • Haldol (Haloperidol)

    • Trilafon (Perphenazine)

    • Mellaril (Thioridazine)

    • Stelazine (Trifluoperazine)

    • Navane (Thiothixene)

    • Loxitane (Loxapine)

    • Moban (Molindone)