From the Guidelines
Gravol (dimenhydrinate) works primarily as an antihistamine that blocks H1 receptors in the brain to prevent nausea and vomiting. It specifically acts on the vestibular system and chemoreceptor trigger zone (CTZ) in the brain stem, which are key areas involved in motion sickness and other causes of nausea. Dimenhydrinate is actually a combination of two compounds: diphenhydramine (an antihistamine) and 8-chlorotheophylline (a mild stimulant related to caffeine that helps counteract the drowsiness caused by diphenhydramine) 1. The medication crosses the blood-brain barrier and competes with histamine for H1 receptor sites, thereby reducing the stimulation of the vestibular nuclei and vomiting center. Some key points to consider when using Gravol include:
- Typical adult dosing is 50-100 mg every 4-6 hours as needed, not exceeding 400 mg in 24 hours, although a study suggests a dose of 25-50 mg tid for nausea and vomiting 1.
- Common side effects include drowsiness, dry mouth, and blurred vision.
- The medication begins working within 30-60 minutes and effects typically last 4-6 hours.
- Patients should be aware that alcohol and other central nervous system depressants can enhance the sedative effects of dimenhydrinate, so these combinations should be avoided. It's also worth noting that H1-receptor antagonists, such as doxylamine, promethazine, and dimenhydrinate, are considered safe first-line pharmacologic antiemetic therapies, if needed 1.
From the FDA Drug Label
While the precise mode of action of dimenhydrinate is not known, it has a depressant action on hyperstimulated labyrinthine function. The mechanism of action of Gravol (dimenhydrinate) is not fully understood, but it is known to have a depressant effect on the labyrinthine function when it is hyperstimulated 2.
- The exact mechanism is unknown
- It has a depressant action on the labyrinthine function when hyperstimulated.
From the Research
Mechanism of Action of Gravol (Dimenhydrinate)
The mechanism of action of Gravol, also known as dimenhydrinate, can be understood by examining its effects on the body and its interaction with various neurotransmitter systems.
- Dimenhydrinate is an H(1) histamine receptor antagonist, which means it works by blocking the action of histamine at H(1) receptors in the brain and other parts of the body 3.
- It also interacts with other neurotransmitter systems, including those using acetylcholine, serotonin, norepinephrine, dopamine, opioids, or adenosine 3.
- The drug has been shown to produce a conditioned place preference in rats, indicating its rewarding properties 4.
- Dimenhydrinate has also been found to stimulate locomotor activity and show sensitization over conditioning sessions in rats 4.
- In humans, dimenhydrinate has been reported to reduce symptoms of motion sickness, possibly by depressing central nervous system activity and suppressing abnormal gastric myoelectric activity 5.
- The drug's ability to reduce motion sickness symptoms may also be related to its effects on the electrogastrogram (EGG), which shows a significant decrease in normal 3 cpm and tachyarrhythmic activity after dimenhydrinate administration 5.
Effects on Motion Sickness
Dimenhydrinate has been shown to be effective in reducing symptoms of motion sickness, including:
- Reducing sodium excretion by sweat, which is a marker of motion sickness 6.
- Decreasing the frequency of binocular nystagmus, which is a common symptom of motion sickness 6.
- Improving subjective well-being and reducing vertigo, as measured by visual analogue scales (VAS) 6.
- Suppressing abnormal gastric myoelectric activity, which may contribute to the development of motion sickness symptoms 5.
Sedative Effects
Dimenhydrinate has sedative effects, which can be both beneficial and detrimental: