Description

Simple

An anti-allergy medication used to treat allergic reactions, such as sneezing, runny nose, itchy or watery eyes, and itching of nose or throat.

Clinical

A H1 receptor antihistamine used in the treatment of seasonal allergies, and various allergic reactions including sneezing, runny nose, itchy/watery eyes, itching of nose or throat, pruritus, urticaria, insect bites/stings, and allergic rashes.

Overview

Diphenhydramine - perhaps known most commonly as its brand name formulation Benadryl - is a first-generation H1 receptor antihistamine that is used extensively for the treatment of seasonal allergies, insect bites and stings, and rashes [9, 10, 11, 16]. However, it also has antiemetic, antitussive, hypnotic, and antiparkinson properties [11, 15]. As histamine receptors exist both peripherally and in the central nervous system, diphenhydramine has been shown to cause sedation due to its competitive antagonism of histamine H1 receptors within the central nervous system [9, Read more

Pharmacology

Indication

Diphenhydramine is a first-generation histamine H1 receptor antagonist (H1 antihistamine) that is widely available as a non-prescription, over-the-counter (OTC) medication. As an OTC medication, diphenhydramine is typically formulated as tablets and creams indicated for use in treating sneezing, run... Read more

Pharmacodynamic

Diphenhydramine has anti-histaminic (H1-receptor), anti-emetic, anti-vertigo and sedative and hypnotic properties [12]. The anti-histam... Read more

Mechanism of action

Diphenhydramine predominantly works via the antagonism of H1 (Histamine 1) receptors [9, Read more

Absorption

Diphenhydramine is quickly absorbed after oral administration with maximum activity occurring in approximately one hour [ Read more

Protein binding

Some prescribing information records the protein binding of diphenhydramine as approximately 78% [17] while others have suggested the medication is about 80 to 85% [ Read more

Volume of distribution

Diphenhydramine is widely distributed throughout the body, including the CNS [17]. Following a 50 mg oral dose of diphenhydramine, the volume of distribution is in the range of 3.3 - 6.8 l/... Read more

Clearance

Values for plasma clearance of a 50 mg oral dose of diphenhydramine has been documented as lying in the range of 600-1300 ml/min [17].

Half life

The elimination half-life ranges from 2.4-9.3 hours in healthy adults [17, Read more

Route of elimination

The metabolites of diphenhydramine are conjugated with glycine and glutamine and excreted in urine [12, Read more

Toxicity

Overdose is expected to result in effects similar to the adverse effects that are ordinarily associated with the use of diphenhydramine, including drowsiness, hyperpyrexia, and anticholinergic effects, among others [ Read more

Adverse Effects

Effect Regions Age Groups Incidences Evidence Type
Dry Eyes US
Varying Reports
Wheezing US
Varying Reports
Tightness of throat US
Varying Reports
Tightness of chest US
Varying Reports
Thickening of bronchial secretions US
Varying Reports
Early menses US
Varying Reports
Urinary Retention US
Varying Reports
Difficult urination US
Varying Reports
Urinary Frequency US
Varying Reports
Nasal Stuffiness US
Varying Reports
Tinnitus US
Varying Reports
Acute labyrinthitis US
Varying Reports
Diplopia US
Varying Reports
Vertigo US
Varying Reports
Paresthesia US
Varying Reports
Blurred vision US
Varying Reports
Insomnia US
Varying Reports
Euphoria US
Varying Reports
Diarrhea US
Varying Reports
Constipation US
Varying Reports
Nausea US
Varying Reports
Vomiting US
Varying Reports
Epigastric distress US
Varying Reports
Anorexia US
Varying Reports
Neuritis US
Varying Reports
Convulsions US
Varying Reports
Sedation US
Varying Reports
Agranulocytosis US
Varying Reports
Dizziness US
Varying Reports
Sleepiness US
Varying Reports
Extrasystoles US
Varying Reports
Tachycardia US
Varying Reports
Thrombocytopenia US
Varying Reports
Hemolytic Anemia US
Varying Reports
Nervousness US
Varying Reports
Excitation US
Varying Reports
Irritability US
Varying Reports
Tremor US
Varying Reports
Fatigue US
Varying Reports
Disturbed coordination US
Varying Reports
Restlessness US
Varying Reports
Confusion US
Varying Reports
Urticaria US
Varying Reports
Drug rash US
Varying Reports
Anaphylactic shock US
Varying Reports
Dryness of nose dryness of throat US
Varying Reports
Hypotension US
Varying Reports
Headache US
Varying Reports
Palpitations US
Varying Reports
Photosensitivity US
Varying Reports

Contraindications

  • Route:
    • Intravenous
    • Intramuscular
  • Dose Form:
    • Injection
  • Regions: US
  • Patient Conditions:
      • Name: Use as a local anesthetic
      • Drugbank Id: DBCOND0108188
  • Route:
    • Intravenous
    • Intramuscular
  • Dose Form:
    • Injection
  • Regions: US
  • Patient Conditions:
      • Name: Nursing mothers
      • Drugbank Id: DBCOND0107390
  • Route:
    • Intravenous
    • Intramuscular
  • Dose Form:
    • Injection
  • Regions: US
  • Age Groups:
    • neonatal
    • premature infants

Food Interactions

Avoid alcohol.

Take before a meal. Take 30 minutes before a meal or 30 minutes before departure for motion sickness.