Brands, Medical Use, Clinical Data
Drug Category
- Histamine H1 Antagonists
- Anti-allergic Agents
- Hypnotics and Sedatives
- Antitussives
- Antipruritics
- Antiparkinson Agents
- Antidyskinetics
- Antiemetics
- Anesthetics
- Ethanolamine Derivatives
Dosage Forms
- Capsule
- Oral solution
- Tablet
- Tablet (chewable)
- Tablet (film-coated)
- Elixir
- Injection
- Cream
- Gel
- Topical solution
- Topical stick
Brands / Synonyms
Airacof; Aleryl; Alledryl; Aller-Med; Allerdryl; Allergan; Allergan B; Allergeval; Allergical; Allergin; Allergina; Allergival; Allermax Caplets; Ambodryl; Amidryl; Antistominum; Antitussive; Antomin; Automin; Bagodryl; Banophen; Banophen Caplets; Baramine; Beldin; Belix; Ben-Allergin; Bena; Benachlor; Benadon; Benadrin; Benadryl; Benadryl Allergy; Benadryl Preservative Free; Benapon; Benodin; Benodine; Benylan; Benylin; Benzantine; Benzhydramine; Benzhydraminum; Benzhydril; Benzhydroamina; Benzhydryl; Betramin; Compoz; Dabylen; Debendrin; Dermistina; Dermodrin; Desentol; Diabenyl; Diabylen; Dibendrin; Dibenil; Dibondrin; Difedryl; Difenhydramin; Difenidramina; Dihidral; Dimedrol; Dimedryl; Diphantine; Diphen; Diphen Cough; Diphenhist; Diphenhist Captabs; Diphenhydramine; Diphenhydramine Base; Diphenhydramine Hcl; Diphenhydramine Hcl Preservative Free; Diphenhydramine Injection; Diphenhydramine Salicylate; Diphenylhydramine; Dormarex 2; Dryistan; Drylistan; Dylamon; Etanautine; Genahist; Histaxin; Hyadrine; Hydramine; Hyrexin; Ibiodral; Medidryl; Mephadryl; Nausen; Nervine Nighttime Sleep-Aid; Novamina; Nytol Quickcaps; Nytol Quickgels; Probedryl; Restamin; Restamine; Rigidil; Rigidyl; Siladryl; Silphen; Sleep-Eze D; Sleep-Eze D Extra Strength; Sominex; Soverin; Syntedril; Syntodril; Torinal; Twilite Caplets; Unisom Sleepgels Maximum Strength; Vena; Vicks Formula 44
Indications
For the treatment of symptoms associated with Vertigo/Meniere's disease, nausea and vomiting, motion sickness and insect bite.
Pharmacology
Diphenhydramine is an antihistamine of the ethanolamine class. Ethanolamine antihistamines have significant antimuscarinic activity and produce marked sedation in most patients. In addition to the usual allergic symptoms, the drug also treats irritant cough and nausea, vomiting, and vertigo associated with motion sickness. It also is used commonly to treat drug-induced extrapyramidal symptoms as well as to treat mild cases of Parkinson's disease. Rather than preventing the release of histamine, as do cromolyn and nedocromil, diphenhydramine competes with free histamine for binding at HA-receptor sites. Diphenhydramine competitively antagonizes the effects of histamine on HA-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. Ethanolamine derivatives have greater anticholinergic activity than do other antihistamines, which probably accounts for the antidyskinetic action of diphenhydramine. This anticholinergic action appears to be due to a central antimuscarinic effect, which also may be responsible for its antiemetic effects, although the exact mechanism is unknown.
Mechanism of Action
Diphenhydramine competes with free histamine for binding at HA-receptor sites. This antagonizes the effects of histamine on HA-receptors, leading to a reduction of the negative symptoms brought on by histamine HA-receptor binding.
Absorption
Quickly absorbed with maximum activity occurring in approximately one hour.
Toxicity
LD50=500 mg/kg (Orally in rats)
Biotrnasformation / Drug Metabolism
Hepatic and renal
Contraindications
Use in Newborn or Premature Infants: This drug should not be used in newborn or premature
infants.
Use in Nursing Mothers: Because of the higher risk of antihistamines for infants generally, and for
newborns and prematures in particular, antihistamine therapy is contraindicated in nursing mothers.
Antihistamines are also contraindicated in the following conditions: Hypersensitivity to diphenhydramine
hydrochloride and other antihistamines of similar chemical structure.
Injection
Use as a Local Anesthetic: Because of the risk of local necrosis, this drug in the parenteral from should
not be used as a local anesthetic.
Drug Interactions
Diphenhydramine hydrochloride has additive effects with alcohol and other CNS depressants (hypnotics, sedatives,
tranquilizers, etc).
MAO inhibitors prolong and intensify the anticholinergic (drying) effects of antihistamines.
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