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Combination of
diphenhydramine antihistamine
8-chlorotheophylline stimulant
CAS number 523-87-5
ATC code  ?
PubChem 10660
DrugBank APRD00924
ChemSpider 10210
Therapeutic considerations
Pregnancy cat.

B (U.S.)

Legal status

OTC (U.S.)

Routes Oral, I.V.

Dimenhydrinate (marketed under brand names Dramamine, Gravol, and Vertirosan) is an over-the-counter drug used to prevent nausea and motion sickness. It is marketed in Portugal as Viabom, but in prescription format.

It is most commonly used as pills, although it is also available in liquid form and in suppositories. This last is particularly useful in the case of persistent vomiting.

It is closely related to diphenhydramine HCl, or Benadryl. The differences relate to the weight-for-weight potency (50 mg dimenhydrinate contains 25 mg of the drug diphenhydramine), delay of action (dimenhydrinate must dissociate into diphenhydramine and its counterion in the body before it is active, therefore diphenhydramine produces effects sooner), and degree of sedation produced. Chemically, dimenhydrinate is a salt of two drugs: diphenhydramine and 8-chlorotheophylline, a chlorinated derivative of the theophylline. Theophylline is very closely related to caffeine and theobromine, mild central nervous system stimulants. It was thought 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 chlorotheophyllinate, so the overall effect is still mostly sedating. Diphenhydramine, an ethanolamine-class antihistamine, is found in most OTC sleep aids and allergy preparations, such as Tylenol PM and Benadryl. It is primarily a H1-antagonist, but also possesses an antimuscarinic effect. It is used in Dramamine to prevent nausea and emesis; however, the development of the chemical meclizine has overtaken its usage (marketed as "Dramamine II") because meclizine doesn't produce as much drowsiness.


[edit] Off-label use

Dimenhydrinate is used as a deliriant at doses of 200 to 1200 mg, although it should be noted that body weight plays a significant part in dosing of any drug. Slang terms for Dramamine used this way include "dime," "dime tabs," "substance D," and "d-house." 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 mild trip. [1] The LD-50 (the lethal dose at which 50% of animals tested produced fatal symptoms) for dimenhydrinate is 500 mg/kg in lab rats (LD50 levels can vary greatly between humans and other animals).

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.

The auditory/visual hallucinations coupled with the ensuing confusion and short-term memory loss often leads to mild or intensive paranoia among the users. Though auditory hallucinations are more common than visual hallucinations, the visuals of a "Dramamine Trip" can seem very real. At higher doses the hallucinations are more frequent, realistic and in some cases, frightening. Taking Dramamine at higher doses is in no way advised or recommended as potential for overdose is a risk. Hallucinations induced by Dramamine abuse are sometimes shared among users; that is, it is common for Dramamine users to hear their own name being called, to see frightening creatures (such as insects or zombies), and to have conversations with non-existing people.

Other CNS effects occur within the limbic system and hippocampus, causing confusion and temporary amnesia due to decreased acetycholine. 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.

[edit] Veterinary use

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[2] and 10 mg for cats; duration of effect is 8 hours.

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