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Dimenhydrinate

Combination of
diphenhydramine	antihistamine
8-chlorotheophylline	stimulant
Clinical data
AHFS/Drugs.com	monograph
MedlinePlus	a607046
Pregnancy cat.	A (AU) B (US)
Legal status	Pharmacy Only (S2) (AU) OTC (US)
Routes	Oral, Rectal, I.V.
Identifiers
CAS number	523-87-5 Y
ATC code	R06AA52
PubChem	CID 10660
DrugBank	DB00985
ChemSpider	10210 Y
UNII	JB937PER5C Y
KEGG	D00520 Y
ChEMBL	CHEMBL1200406 N
N (what is this?)  (verify)

Dimenhydrinate (in US marketed under brand names Dramamine, Driminate, Gravol, Gravamin, Vomex, and Vertirosan) is an over-the-counter drug used to prevent nausea and motion sickness. It is marketed in Brazil as Dramin, in Canada as Gravol, in Ecuador as Anautin, in Hungary as Daedalon, in Italy as Xamamina, in Indonesia as Antimo, in Portugal as Viabom, and in Thailand as ไดเมนนีน (Dị men nīn). It is most commonly prepared as tablets, although it is also available in liquid form and in suppositories. Chemically, dimenhydrinate is a salt of two drugs: diphenhydramine, and 8-chlorotheophylline, a chlorinated derivative of theophylline.

Pharmacology [edit]

Diphenhydramine is the primary constituent of dimenhydrinate and dictates the primary effect. The main difference is a lower potency due to being combined with Theophylline. 50 mg dimenhydrinate contains 27.2 mg of diphenhydramine.

Theophylline was added in order to counteract drowsiness. Theophylline is very closely related to caffeine and theobromine, mild central nervous system stimulants. It was thought by scientists that by combining the antiemetic effects of diphenhydramine with a stimulant, the extreme drowsiness induced by the former could be mitigated somewhat by the latter. The sedation caused by diphenhydramine, however, is substantially stronger than the stimulation caused by chlorotheophylline, so the overall effect is still mostly sedating. While dimenhydrinate is still used to prevent nausea and emesis, the development of the chemical meclozine has overtaken its usage (marketed as "Dramamine II") because meclozine is less likely to cause drowsiness.

Recreational use [edit]

Dimenhydrinate is used as a deliriant at doses of 1200 to 2000 mg, although body weight plays a significant part in dosing of this drug. Slang terms for Dramamine used this way include "dime," "dime tabs," "D-Q," "substance D," "d-house," and "drams." Frequent users of Dramamine are sometimes called Dramatists, a pun on the name. Tripping on Dramamine is sometimes referred to as Dramatizing or "going a dime a dozen," a reference to the amount of Dramamine tabs generally necessary for a trip. The LD₅₀ (the dose at which 50% of animals tested produced fatal symptoms) for dimenhydrinate is 500 mg/kg in lab rats, which may suggest that a human of typical weight would need to ingest a greater than tenfold amount of a psychoactive dose in order to risk death: However it is important to note that LD₅₀ varies greatly even between mammals and is almost always lower for humans than for rats. As well, it is possible that a significant proportion may experience serious or fatal reactions at doses far lower than the LD₅₀.

Many users report a side effect profile consistent with tropane glycoalkaloidal (e.g. atropine) poisoning as both show antagonism of muscarinic acetylcholine receptors in both the central and autonomic nervous system, which inhibits various signal transduction pathways. In the CNS, dimenhydrinate readily crosses the blood-brain barrier, exerting effects within the visual and auditory cortex.

Other CNS effects occur within the limbic system and hippocampus, causing confusion and temporary amnesia due to decreased acetylcholine signaling. Toxicology also manifests in the autonomic nervous system, primarily at the neuromuscular junction, resulting in ataxia and extrapyramidal side-effects and the feeling of heaviness in the legs, and at sympathetic post-ganglionic junctions, causing urinary retention, pupil dilation, tachycardia, irregular urination, and dry red skin caused by decreased exocrine gland secretions, and mucous membranes. Considerable overdosage can lead to myocardial infarction (heart attack), serious ventricular dysrhythmias, coma and death. Such a side-effect profile is thought to give ethanolamine-class antihistamines a relatively low abuse liability. The specific antidote for dimenhydrinate poisoning is physostigmine, usually given by IV in a hospital.

Veterinary use [edit]

Dimenhydrinate has successfully been used as an antiemetic and sedative in housepets. It is commonly used to reduce the effects of idiopathic vestibular syndrome. The suggested dosage is 50 mg for dogs^[1] and 10 mg for cats; duration of effect is 8 hours.

This dosage though is not a proper measure for all pets and should be adjusted by weight.

References [edit]

Notes