Benadryl (Diphenhydramine)
Diphenhydramine
Brand names(s): AllerMax®, Banophen®, Benadryl®, Diphedryl®, Dytan®, Nytol® QuickCaps, Simply Sleep™ | Aler-Dryl® | Aller-Dryl® Topical | Allergia-C® | Allergy Cream | Altaryl® | Banaril™ | Banophen® Elixir | Ben-Tann | Benadryl® Allergy Dye Free | Benadryl® Allergy Kapseals® | Benadryl® Allergy Ultratab® | Benadryl® Dye Free | Benadryl® Extra Strength | Benadryl® Gel | Benadryl® Itch Relief Stick Extra Strength Stick | Benadryl® Itch Stopping Cream | Benekraft-25™ | Calm-Aid® | Childrens Benadryl® | Childrens Benadryl® Allergy | Childrens Benadryl® Allergy Fastmelt™ | Childrens Benadryl® Dye-Free Allergy | Complete Allergy | Complete Allergy Relief | Compoz® Nighttime Sleep Aid | Dermamycin® | Dermarest® Anti-Itch | Dimine™ 10 | Dimine™ 50 | Diphedryl® Dye Free Allergy | Diphen® | Diphen® AF | Diphen® Cough | Diphenadryl® | Diphenhist® | Diphenhist® Cream | Diphenyl® | Diphenylin® | DPH® | Dytan® Chewable | Equate® Allergy Medication | Equate® Childrens Allergy Elixir | Expec™ | Genahist® | Hydramine® | Maximum Night-Time Sleep Aid | Nervine® | Night Time™ Sleep-Aid | Nu-Med® | Pardryl® | Phendry® | Q-Dryl® | Quenalin® | Restfully Sleep | Scot-Tussin® Allergy Relief Formula | Siladryl® | Siladryl® DAS | Silphen® Cough | Sleep Aid Liquid Gels | Sleep Tab® II | Sleep Tabs® | Sleep-ettes® | Sleep-Eze® 3 | Sleepinal® | Sominex® | Somnicaps® | Theraflu® Thin Strips™ Multi Symptom | Total Allergy® | Triaminic® Thin Strips™ Cough & Runny Nose | Trux Adryl™ | Tusstat® | Twilite® | Uni-Hist® | Uni-Tann | Unisom® Sleepgels Maximum Strength | Valu-Dryl® | Valu-Dryl® Topical | Wal-dryl Allergy Solution
Classification:
Antihistamines
» H1-blockers
» Sedating H1-blockers
Dermatological Agents
» Antihistamines
Psychotropic Agents
» Anxiolytics, Sedatives, and Hypnotics
Description: Diphenhydramine is an H1-antagonist of the ethanolamine class. Other members of this group include carbinoxamine, clemastine, dimenhydrinate (a salt of diphenhydramine), doxylamine, phenyltoloxamine and others. Ethanolamine H1-antagonists have significant antimuscarinic activity and produce marked sedation in most patients. In general, gastrointestinal side effects are minimal. Diphenhydramine is a popular antihistamine due to its relative safety after oral or parenteral administration. In addition to the usual allergic symptoms, the drug also treats irritant cough, although the airway drying effect may be counterproductive. Because of its anticholinergic properties, diphenhydramine is effective in the relief of 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. Diphenhydramine was originally approved by the FDA in 1946 as a prescription-only drug but was later changed to non-prescription (OTC) status. Due to its ability to induce drowsiness, it is also promoted as an OTC hypnotic.
Mechanism of Action: Diphenhydramine does not prevent the release of histamine, as do cromolyn and nedocromil, but rather competes with free histamine for binding at H1-receptor sites. Diphenhydramine competitively antagonizes the effects of histamine on H1-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. Blockade of H1-receptors also suppresses the formation of edema, flare, and pruritus that result from histaminic activity.
H1-antagonists possess anticholinergic properties in varying degrees; 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. Diphenhydramine has a direct suppressive action on the cough center and causes sedation via CNS depression. Topical diphenhydramine provides local relief from insect bites, minor burns, sunburn, or minor abrasions, possibly due to an anesthetic effect resulting from decreased permeability of nerve cell membranes to sodium ions (preventing the transmission of nerve impulses). Following prolonged use of diphenhydramine, tolerance can occur, but this may be beneficial because of reduced sedative effects.
Allergy Cream (Cream 2 %) 
Pharmacokinetics: Diphenhydramine may be administered orally, topically, intravenously, or intramuscularly. In general, H1-antagonists are well absorbed from the GI tract, but they have variable solubility, which ultimately affects the onset of action. Less soluble H1-antagonists have a slower onset of action and are less likely to cause toxicity. Onset of action following oral administration of diphenhydramine occurs in 15 - 30 minutes, with peak concentrations occurring in about 2 - 4 hours. The duration of action ranges from 4 - 6 hours. The maximum sedative effect of the drug occurs between 1 - 3 hours. The onset of antiextrapyramidal effects following an intramuscular injection is 15 - 30 minutes. Diphenhydramine is highly protein-bound. It is widely distributed in body tissues and fluids, and it crosses the placenta and is excreted into breast milk.
Metabolism occurs in the liver to produce diphenylmethoxyacetic acid, which then becomes conjugated; other metabolites are also formed. Plasma half-life is between 2 - 8 hours. Most unchanged drug and metabolites are excreted renally within 24 - 48 hours of a dose.
[1 of 11 - Click here to see more photos]
[ Revised 6/21/2006 3:34:00 PM ]
Related entries
Syndicate
|
