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, 15]. However, it also has antiemetic, antitussive, hypnotic, and antiparkinson properties [11, 14]. 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% [16] 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 [16]. 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 [16].

Half life

The elimination half-life ranges from 2.4-9.3 hours in healthy adults [16, 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

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 with food.

Interactions

Type in a drug name to check for interaction with Diphenhydramine
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  • Paracetamol(acetaminophen)
  • Paxil(paroxetine)
  • Pamelor(nortriptyline)
  • Panadol(acetaminophen)
  • Patanol(olopatadine ophthalmic)
  • Pataday(olopatadine ophthalmic)
  • Parnate(tranylcypromine)
  • Pazeo(olopatadine ophthalmic)
(R)-warfarin
The metabolism of (R)-warfarin can be decreased when combined with Diphenhydramine.
(S)-Warfarin
The metabolism of (S)-Warfarin can be decreased when combined with Diphenhydramine.
1-(2-Phenylethyl)-4-phenyl-4-acetoxypiperidine
The metabolism of Diphenhydramine can be decreased when combined with 1-(2-Phenylethyl)-4-phenyl-4-acetoxypiperidine.
1,10-Phenanthroline
The therapeutic efficacy of Diphenhydramine can be decreased when used in combination with 1,10-Phenanthroline.
2,5-Dimethoxy-4-ethylamphetamine
2,5-Dimethoxy-4-ethylamphetamine may decrease the sedative and stimulatory activities of Diphenhydramine.
2,5-Dimethoxy-4-ethylthioamphetamine
2,5-Dimethoxy-4-ethylthioamphetamine may decrease the sedative and stimulatory activities of Diphenhydramine.
4-Bromo-2,5-dimethoxyamphetamine
4-Bromo-2,5-dimethoxyamphetamine may decrease the sedative and stimulatory activities of Diphenhydramine.
4-Methoxyamphetamine
The risk or severity of adverse effects can be increased when Diphenhydramine is combined with 4-Methoxyamphetamine.
5-methoxy-N,N-dimethyltryptamine
The risk or severity of adverse effects can be increased when Diphenhydramine is combined with 5-methoxy-N,N-dimethyltryptamine.
7-Nitroindazole
The risk or severity of adverse effects can be increased when Diphenhydramine is combined with 7-Nitroindazole.
7,8-Dichloro-1,2,3,4-tetrahydroisoquinoline
The risk or severity of adverse effects can be increased when 7,8-Dichloro-1,2,3,4-tetrahydroisoquinoline is combined with Diphenhydramine.
Abatacept
The metabolism of Diphenhydramine can be increased when combined with Abatacept.
Abediterol
The risk or severity of Tachycardia can be increased when Diphenhydramine is combined with Abediterol.
Abexinostat
The risk or severity of QTc prolongation can be increased when Diphenhydramine is combined with Abexinostat.
Abiraterone
The metabolism of Diphenhydramine can be decreased when combined with Abiraterone.
Acebutolol
The metabolism of Acebutolol can be decreased when combined with Diphenhydramine.
Acenocoumarol
The metabolism of Acenocoumarol can be decreased when combined with Diphenhydramine.
Acepromazine
The risk or severity of adverse effects can be increased when Diphenhydramine is combined with Acepromazine.
Aceprometazine
The risk or severity of adverse effects can be increased when Diphenhydramine is combined with Aceprometazine.
Acetazolamide
The risk or severity of adverse effects can be increased when Acetazolamide is combined with Diphenhydramine.
16 References
  1. 1 . Raphael GD, Angello JT, Wu MM, Druce HM: Efficacy of diphenhydramine vs desloratadine and placebo in patients with moderate-to-severe seasonal allergic rhinitis. Ann Allergy Asthma Immunol. 2006 Apr;96(4):606-14.PubMed: 16680933
  2. 2 . Abdi A, Rose E, Levine M: Diphenhydramine overdose with intraventricular conduction delay treated with hypertonic sodium bicarbonate and i.v. lipid emulsion. West J Emerg Med. 2014 Nov;15(7):855-8. doi: 10.5811/westjem.2014.8.23407. Epub 2014 Sep 19.PubMed: 25493135
  3. 3 . Halpert AG, Olmstead MC, Beninger RJ: Mechanisms and abuse liability of the anti-histamine dimenhydrinate. Neurosci Biobehav Rev. 2002 Jan;26(1):61-7.PubMed: 11835984
  4. 4 . Jaju BP, Wang SC: Effects of diphenhydramine and dimenhydrinate on vestibular neuronal activity of cat: a search for the locus of their antimotion sickness action. J Pharmacol Exp Ther. 1971 Mar;176(3):718-24.PubMed: 4329456
  5. 5 . Flake ZA, Scalley RD, Bailey AG: Practical selection of antiemetics. Am Fam Physician. 2004 Mar 1;69(5):1169-74.PubMed: 15023018
  6. 6 . Paton DM, Webster DR: Clinical pharmacokinetics of H1-receptor antagonists (the antihistamines). Clin Pharmacokinet. 1985 Nov-Dec;10(6):477-97.PubMed: 2866055
  7. 7 . Akutsu T, Kobayashi K, Sakurada K, Ikegaya H, Furihata T, Chiba K: Identification of human cytochrome p450 isozymes involved in diphenhydramine N-demethylation. Drug Metab Dispos. 2007 Jan;35(1):72-8. doi: 10.1124/dmd.106.012088. Epub 2006 Oct 4.PubMed: 17020955
  8. 8 . Rodrigues WC, Castro C, Catbagan P, Moore C, Wang G: Immunoassay screening of diphenhydramine (Benadryl(R)) in urine and blood using a newly developed assay. J Anal Toxicol. 2012 Mar;36(2):123-9. doi: 10.1093/jat/bkr015.PubMed: 22337782
  9. 9 . StatPearls [Internet]: Diphenhydramine Link
  10. 10 . Electronic Medicines Compendium: Histergan (diphenhydramine hydrochloride) Tablets Patient Information Link
  11. 11 . Electronic Medicines Compendium: Histergan (diphenhydramine hydrochloride) Cream Monograph Link
  12. 12 . Electronic Medicines Compendium: Boots Sleepeaze (diphenhydramine hydrochloride) 50mg Tablets Monograph Link
  13. 13 . Electronic Medicines Compendium: Nytol One-A-Night (diphenhydramine hydrochloride) Monograph Link
  14. 14 . Diphenhydramine Hydrochloride Injection, USP FDA Label File
  15. 15 . DIPHENHYDRAMINE- diphenhydramine hcl tablet, coated DailyMed FDA Label File
  16. 16 . Benylin Chesty Coughs UK MHRA Product Information File