Mephadryl - General Information
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.
Pharmacology of Mephadryl
Mephadryl 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. Mephadryl 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.
Mephadryl for patients
Patients taking diphenhydramine hydrochloride should be advised that this drug may cause drowsiness and has an additive effect with alcohol.
Patients should be warned about engaging in activities requiring mental alertness such as driving a car or operating appliances, machinery, etc.
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.
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.
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.
Additional information about Mephadryl
Mephadryl Indication: For the treatment of symptoms associated with Vertigo/Meniere's disease, nausea and vomiting, motion sickness and insect bite.
Mechanism Of Action: Mephadryl 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.
Drug Interactions: Atomoxetine The CYP2D6 inhibitor could increases the effect and toxicity of atomoxetine
Donepezil Possible antagonism of action
Galantamine Possible antagonism of action
Mesoridazine Increased risk of cardiotoxicity and arrhythmias
Rivastigmine Possible antagonism of action
Thioridazine Increased risk of cardiotoxicity and arrhythmias
Food Interactions: Avoid alcohol.
Take with food.
Generic Name: Diphenhydramine
Synonyms: Diphenhydramine Base; Diphenhydramine Hcl; Diphenhydramine Salicylate; Diphenylhydramine
Drug Category: Histamine H1 Antagonists; Anti-Allergic Agents; Hypnotics and Sedatives; Antitussives; Antipruritics; Antiparkinson Agents; Antidyskinetics; Antiemetics; Anesthetics; Ethanolamine Derivatives
Drug Type: Small Molecule; Approved
Absorption: Quickly absorbed with maximum activity occurring in approximately one hour.
Toxicity (Overdose): LD50=500 mg/kg (orally in rats). Considerable overdosage can lead to myocardial infarction (heart attack), serious ventricular dysrhythmias, coma and death.
Protein Binding: 98 to 99%
Biotransformation: Hepatic and renal
Half Life: 1-4 hours
Dosage Forms of Mephadryl: Liquid Intravenous
Tablet, chewable Oral
Chemical IUPAC Name: 2-[di(phenyl)methoxy]-N,N-dimethylethanamine
Chemical Formula: C17H21NO
Diphenhydramine on Wikipedia: https://en.wikipedia.org/wiki/Diphenhydramine
Organisms Affected: Humans and other mammals