II. Indications

III. Mechanism

  1. Sedating Antihistamine
  2. H1 Receptor Antagonist
  3. Ethanolamine with strong Anticholinergic activity

IV. Dosing: Standard

  1. Adult (age >=12 years): 25-50 mg PO/IV/IM every 6 hours (maximum: 300 to 400 mg/day)
  2. Child (age <12 years): 5 mg/kg/day divided four times daily (12.5 mg/5 ml)
    1. Age 2 to 5 years: 6.25 mg every 4 hours as needed
    2. Age 6 to 12 years: 12.5 mg every 4 years as needed

V. Dosing: Local Injection

  1. Diphenhydramine may be used for local injection when patients are allergic to other Local Anesthesia
  2. Diphenhydramine 1% (for Local Anesthesia)
    1. Dilute Diphenhydramine 5% in Normal Saline (1:4)
    2. Longer delay to onset of action than Lidocaine
    3. Shorter duration of action than Lidocaine

VI. Adverse Effects

  1. See Sedating Antihistamine
  2. Poisoning
    1. See Anticholinergic Toxicity
    2. Mild Overdose
      1. Causes sedation and muscarinic Anticholinergic Toxicity (Dry Mouth, Tachycardia, Mydriasis, Urinary Retention)
    3. Severe Overdose
      1. Causes Agitation, Delirium, Hallucinations, Seizures and coma
      2. Diphenhydramine blocks myocardial Sodium and Potassium channels (Wide QRS, QTc Prolongation)
      3. Diphenhydramine Overdose is responsible for >3% of U.S. Overdose deaths (within top 15 drugs)
    4. References
      1. Lacey and Dietrich (2023) Crit Dec Emerg Med 37(3): 18-9

VII. Safety

  1. Pregnancy Category B
  2. Avoid in Lactation

VIII. Pharmacokinetics

  1. Duration 4 to 6 hours
  2. Hepatic metabolism
  3. Renal Clearance

X. References

  1. Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 90
  2. Hamilton (2020) Tarascon Pocket Pharmacopoeia

Images: Related links to external sites (from Bing)

Related Studies

Cost: Medications

diphenhydramine (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
DIPHENHYDRAMINE 12.5 MG/5 ML Generic OTC $0.01 per ml
DIPHENHYDRAMINE 25 MG CAPSULE Generic OTC $0.03 each
DIPHENHYDRAMINE 25 MG TABLET Generic OTC $0.04 each
DIPHENHYDRAMINE 50 MG CAPSULE Generic OTC $0.02 each
DIPHENHYDRAMINE 50 MG/ML VIAL Generic $0.85 per ml
banophen (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
BANOPHEN 25 MG CAPSULE Generic OTC $0.03 each
BANOPHEN 25 MG TABLET Generic OTC $0.04 each
BANOPHEN 50 MG CAPSULE Generic OTC $0.02 each
BANOPHEN ANTI-ITCH 2% CREAM Generic OTC $0.05 per gram
diphen (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
DIPHENHIST 25 MG CAPSULE Generic OTC $0.03 each
DIPHENOXYLATE-ATROPINE 2.5-0.025 MG TABLET Generic $0.18 each
siladryl (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
SILADRYL 12.5 MG/5 ML LIQUID Generic OTC $0.02 per ml

Ontology: Diphenhydramine (C0012522)

Definition (CHV) a drug used to treat allergy symptoms
Definition (CHV) a drug used to treat allergy symptoms
Definition (NCI) A first generation antihistamine and ethanolamine with sedative and anti-allergic properties. Diphenhydramine competitively inhibits the histamine-1 (H1) receptor, thereby alleviating the symptoms caused by endogenous histamine on bronchial, capillary and gastrointestinal smooth muscles. This prevents histamine-induced bronchoconstriction, vasodilation, increased capillary permeability, and GI smooth muscle spasms.
Definition (NCI_NCI-GLOSS) A drug used to treat allergies and relieve cough and itching caused by insect bites, sunburn, and poison oak or ivy. It is also used to treat mild Parkinson disease, to prevent and treat motion sickness, to relieve cough and cold symptoms, and as a sleep aid. It is a type of antihistamine.
Definition (MSH) A histamine H1 antagonist used as an antiemetic, antitussive, for dermatoses and pruritus, for hypersensitivity reactions, as a hypnotic, an antiparkinson, and as an ingredient in common cold preparations. It has some undesired antimuscarinic and sedative effects.
Definition (CSP) histamine H1 antagonist used as an antiemetic, antitussive, for dermatoses and pruritus, for hypersensitivity reactions, as a hypnotic, an antiparkinson, and as an ingredient in common cold preparations; it has some undesired antimuscarinic and sedative effects.
Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D004155
SnomedCT 256043008, 26458009, 372682005
LNC LP16116-3, MTHU019051, MTHU013946
English Benhydramin, Benzhydramine, Diphenhydramine, Diphenylhydramin, Diphenylhydramine, 2-Diphenylmethoxy-N,N-dimethylethylamine, diphenylhydramine, Ethanamine, 2-(diphenylmethoxy)-N,N-dimethyl-, diphenhydramines (medication), diphenhydramines, diphenhydramine (medication), Diphenhydramine [Chemical/Ingredient], DIPHENHYDRAMINE, diphenhydrAMINE, O-Benzhydryldimethylaminoethanol, 2-(Diphenylmethoxy)-N,N-dimethylethylamine, Rigidyl, Probedryl, diphenhydramine, Diphenhydramine product, Diphenhydramine (product), Diphenhydramine (substance), Diphenhydramine [dup] (substance)
Swedish Difenhydramin
Czech difenhydramin
Finnish Difenhydramiini
Russian DIFENGIDRAMIN, DIMEDROL, BENGIDRAMIN, DIFENILGIDRAMIN, БЕНГИДРАМИН, ДИМЕДРОЛ, ДИФЕНГИДРАМИН, ДИФЕНИЛГИДРАМИН
Japanese ベンヒドラミン, ジフェンヒドラミン, ジフェニルヒドラミン
Italian 2-difenilmetossi-N,N-dimetiletanamina, Difenilidramina
Polish Difenhydramina, Benzhydramina
Spanish difenhidramina (producto), difenhidramina (sustancia), difenhidramina, Benhidramina, Difenhidramina, Difenilhidramina
French Diphénhydramine
German Benhydramin, Diphenhydramin, Diphenylhydramin
Portuguese Benidramina, Difenidramina, Difenilidramina

Ontology: Benadryl (C0700899)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D004155
English Benadryl