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Dimenhydrinate
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| Combination of | |
| diphenhydramine | antihistamine |
| 8-chlorotheophylline | stimulant |
| Identifiers | |
| CAS number | |
| ATC code | ? |
| PubChem | |
| DrugBank | |
| ChemSpider | |
| 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. In actuality, the sedation caused by diphenhydramine is substantially stronger than the stimulation caused by chlorotheophyllinate. 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.
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Recreational use
Dimenhydrinate is sometimes used recreationally as a deliriant at doses of 200 - 1200 mg, although it should be noted that body weight plays a significant part in dosing of any drug. The LD-50 or at what level 50% of animals tested produced fatal symptoms for dimenhydrinate is 500 mg/kg in lab rats (LD50 levels can vary greatly between humans and animals).
The mental effects can be described as "lucid dreaming" involving visual and auditory hallucinations that, unlike those experienced with most psychedelic drugs, often cannot be readily distinguished from reality. People who consume a high recreational dose can possibly find themselves interacting normally with a hallucination and have normal conversations with, for example, a hallucination of a family member. A common sometimes frightening hallucination is of insects and spiders. Hallucinations are more frequent and unpleasant in a setting with little or no light. Inexperienced users of deliriants are likely to panic. Dramamine is therefore recommended to be taken with a "sitter", an individual not under the effects of drugs.
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 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.
The intoxication can be described with the following saying “blind as a bat, dry as a bone, red as a beet, mad as a hatter, and hot as a hare."citation needed Blind as a bat meaning blurry and impaired vision. Dry as a bone meaning the inhibiting effect on sweat and saliva making the mouth and skin dry as a "bone." Red as beet meaning the observed effect of the skin turning red with someone using deliriants. Mad as a hatter referring to the frank delirium and true hallucinations (unlike LSD or Psychedelic Mushrooms; which only cause alterations in perception, deliriants cause true hallucinations as they can't be distinguished from reality and are usually extremely real looking) induced effect. Hot as a hare meaning the user of the deliriant becomes extremely hot because of lack of sweat and saliva production and significant increase in heart rate and blood pressure.
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 dogs1 and 10 mg for cats; duration of effect is 8 hours.
See also
References
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