Dimenhydrinate was first identified in 1947 by allergists at Johns Hopkins Hospital who were researching treatments for hives when they unexpectedly discovered its effectiveness in preventing motion sickness. Clinical trials, including those conducted on U.S. troops, confirmed its benefits, and the findings were publicly announced in 1949. The drug was patented in 1950 and introduced to the market under the brand name Dramamine. Today, dimenhydrinate is available over the counter (OTC) as an antihistamine used to prevent and relieve motion sickness symptoms such as nausea, vomiting, and dizziness. It acts on the brain’s balance centers and possesses notable central nervous system (CNS) depressant and anticholinergic effects.
BRAND NAMES
Dimenhydrinate is marketed globally under various brand names, with Dramamine being the most common and widely recognized.
Other brand names for dimenhydrinate:
Calm-X
metabs
Dinate
Driminate
Dymenate
MECHANISM OF ACTION
Dimenhydrinate is a theoclate salt that dissociates into diphenhydramine and 8-chlorotheophylline. Although its exact mechanism of action is not fully understood, diphenhydramine is believed to help stabilize balance by exerting antimuscarinic effects and blocking histamine H1 receptors. Meanwhile, 8-chlorotheophylline is thought to counteract the sedative effects of diphenhydramine by blocking adenosine receptors, leading to mild stimulation.
PHARMACOKINETICS:
Absorption
An oral film-coated tablet containing 50 mg of dimenhydrinate achieves a maximum plasma concentration (Cmax) of 72.6 ng/mL approximately 2.7 hours after administration. In comparison, a 100 mg suppository reaches a Cmax of 112.2 ng/mL at around 5.3 hours post-dose.
Distribution
After administration, dimenhydrinate is extensively distributed throughout body tissues. It is efficiently absorbed and can cross important physiological barriers such as the blood-brain and placental barriers, with small quantities also detected in breast milk.
Metabolism
After absorption, dimenhydrinate undergoes primary metabolism in the liver, where it separates into diphenhydramine and 8-chlorotheophylline. The diphenhydramine component is largely responsible for the drug’s pharmacological activity.
Excretion
Dimenhydrinate is predominantly eliminated in the urine, primarily as metabolites. A very small percentage of the drug is excreted unchanged.
PHARMACODYNAMICS
Dimenhydrinate is an antihistamine with anticholinergic properties that primarily works by blocking H1 receptors in the vestibular system. By reducing signals to the brain’s vomiting center, it helps prevent nausea, vomiting, and dizziness. The diphenhydramine component provides most of the therapeutic effects, while 8-chlorotheophylline counteracts sedation. Its exact mechanism is not fully understood but involves stabilization of equilibrium. This combination makes it effective for motion sickness and related vestibular disturbances.
ADMINISTRATION
The medication Dimenhydrinate can be given by mouth, injected into a muscle (IM), or administered intravenously (IV). For prevention of motion-sickness, the oral dose is usually taken about 30 to 60 minutes before travel or exposure to motion. After oral administration the anti-emetic effect generally begins within about 15 to 30 minutes, and following an intramuscular injection it typically starts in about 20 to 30 minutes. The exact dose and frequency vary depending on the patient’s age and the clinical indication, so the prescribing clinician’s instructions should be strictly followed.
DOSAGE AND STRENGTH
For adults and adolescents aged 12 years and older, the usual dosing of Dimenhydrinate for motion-sickness is 50 to 100 mg orally every 4 to 6 hours, with a maximum of 400 mg in 24 hours. For children aged 6 to under 12 years, the recommended dose is 25 to 50 mg every 6 to 8 hours, not exceeding about 150 mg per day. For children aged 2 to under 6 years, the dose is 12.5 to 25 mg every 6 to 8 hours, with a daily maximum of about 75 mg. In addition, the medication is available in various strengths such as 50 mg tablets and liquid forms (for example 12.5 mg per 4 mL). Adjustments may be required for elderly individuals or those with liver or kidney impairment.
DRUG INTERACTIONS
When used together, Dimenhydrinate can amplify the effects of other central nervous system (CNS) depressants such as alcohol, sedatives, and hypnotics — therefore combined use requires caution to prevent excessive sedation. Moreover, because it possesses anticholinergic properties, it may enhance the anticholinergic effects of other medications (for example, tricyclic antidepressants or antihistamines) and can reduce the effectiveness of acetylcholinesterase inhibitors. In addition, if it’s used alongside ototoxic drugs (such as certain aminoglycoside antibiotics), Dimenhydrinate may mask the early signs of ototoxicity, delaying detection of ear-related harm.
FOOD INTERACTIONS
There is no well-documented specific food interaction for dimenhydrinate; that is, no particular foods are known to markedly alter its absorption or effect according to standard sources. However, because the drug can cause drowsiness and dizziness, it is advisable to avoid alcohol or heavy meals before activities requiring alertness. Some product information suggests avoiding alcohol as it may intensify drowsiness.
CONTRAINDICATIONS
Dimenhydrinate should not be used in individuals with known hypersensitivity to the drug or its components. It is contraindicated in children under 2 years of age (for many formulations) unless under strict medical direction. Additional contraindications or reasons for caution include narrow-angle glaucoma, urinary bladder neck obstruction or prostatic hypertrophy (due to anticholinergic effects), severe respiratory conditions (e.g., asthma, COPD), seizure disorders, and situations where drowsiness or impaired coordination would pose serious risk.
SIDE EFFECTS
Drowsiness or sedation (most frequent)
Dizziness or unsteadiness
Dry mouth, dry throat
Blurred vision or visual disturbances
Palpitations, tachycardia
OVER DOSE
An overdose of dimenhydrinate, which is an antihistamine used for motion sickness, can lead to a condition known as anticholinergic toxicity. The severity of the overdose is directly related to the amount taken, with symptoms starting in the central nervous system (CNS) and quickly affecting major organ systems. Early signs typically include marked drowsiness, dry mouth, blurred vision, and difficulty urinating, reflecting the drug's potent anticholinergic effects.
TOXICITY
Dimenhydrinate has a high potential for toxicity in large doses and an overdose can lead to severe complications including seizures, life-threatening heart rhythm disturbances, coma, and death. It is not a universally safe medication and must be used strictly as directed.
