GRAVINATE TABLETS

Indications

• Motion sickness
• Nausea
• Vomiting
• Vertigo

Dosage

Children: For children aged 2 to 6 years, the dose is typically 12.5 to 25 mg every 6 to 8 hours as needed, not exceeding 75 mg in 24 hours. For children aged 6 to 12 years, the dose is generally 25 to 50 mg every 6 to

Adults: For adults, the usual dose is 50 to 100 mg taken orally every 4 to 6 hours as needed, not exceeding 400 mg in a 24-hour period.

Mechanism of action

Dimenhydrinate acts primarily through the antimuscarinic effects of diphenhydramine and histamine H1 antagonism. Although the exact mechanism is not fully understood, it is believed to inhibit excitatory impulses from the vestibular apparatus to the central nervous system, thus mitigating symptoms of motion sickness. Additionally, 8-chlorotheophylline may counteract the sedative effects of diphenhydramine by blocking adenosine receptors.

Pharmacodynamics

Dimenhydrinate is effective in preventing and treating nausea, vomiting, and vertigo associated with motion sickness. Its efficacy is due to its action on the vestibular nuclei and the vomiting center in the brain. The drug has a rapid onset of action, but patients should be advised about its sedative properties, including drowsiness, and to avoid alcohol or other central nervous system depressants.

Pharmacokinetics

Dimenhydrinate is rapidly absorbed following oral administration, with peak plasma concentrations occurring shortly after ingestion. The drug is metabolized in the liver and eliminated primarily via the kidneys. The short half-life necessitates dosing every few hours for sustained relief of symptoms. Its sedative effects can impact activities requiring alertness.

Adverse effects

• Drowsiness
• Dry mouth
• Dizziness
• Constipation
• Blurred vision

Interactions

• clozapine+dimenhydrinate: Unknown (additive effect)
• antipsychotics, second generation+dimenhydrinate: Unknown (additive effect)

Precautions

• Caution in patients with glaucoma
• Caution in patients with prostate hypertrophy
• Caution in patients with a history of seizures
• Avoid use in the elderly due to increased sensitivity to anticholinergic effects

Pregnancy

Use only if clearly needed and after a careful risk-benefit assessment.

Breast-feeding

Excreted in breast milk; use with caution.

Storage

Store at room temperature, away from moisture and heat.

Formulations

• Tablets
• Oral solution
• Chewable tablets

Mechanism of action

Dimenhydrinate is a theoclate salt that separates into [diphenhydramine] and [8-chlorotheophylline]. While the exact mechanism of action is unknown, diphenhydramine is theorized to reduce disturbances to equilibrium through antimuscarinic effects or histamine H1 antagonism. 8-chlorotheophylline may produce excitation through blocking adenosine receptors, reducing the drowsiness produced by diphenhydramine. IT IS ESSENTIAL TO NOTE THAT NEITHER H1...BLOCKERS INHIBIT HISTAMINE RELEASE. ...EFFECTS OF HISTAMINE ANTAGONISTS...FACILITATE RELEASE. BENEFICIAL EFFECTS OF HISTAMINE ANTAGONISTS ARE THUS CONFINED TO ANTAGONISM OF RESPONSES TO HISTAMINE THAT IS RELEASED. /ANTIHISTAMINES/ DRUGS USED TO BLOCK HISTAMINE RECEPTORS FALL INTO THAT LARGE GROUP OF PHARMACOLOGICAL ANTAGONISTS THAT APPEAR TO ACT BY OCCUPYING "RECEPTIVE SITES" ON EFFECTOR CELL, TO EXCLUSION OF AGONIST MOLECULES, WITHOUT THEMSELVES INITIATING RESPONSE. TYPICALLY...COMPETITIVE & REVERSIBLE. /ANTIHISTAMINES/ ...ANTIHISTAMINES EFFECTIVE IN MOTION SICKNESS ACT BY VIRTUE OF CENTRAL ANTAGONISM OF ACH... ACT BY BLOCKING EXCITATORY LABYRINTHINE IMPULSES @ CHOLINERGIC SYNAPSES IN REGION OF VESTIBULAR NUCLEI. /ANTIHISTAMINES/ ...MOTION SICKNESS. ...STIMULATION OF VESTIBULAR APPARATUS...& THAT VESTIBULAR CEREBELLAR MIDBRAIN "INTEGRATIVE VOMITING CENTER" & MEDULLARY CHEMORECEPTIVE TRIGGER ZONE ARE SOMEHOW INVOLVED. /ANTIHISTAMINES/

Pharmacodynamics

Dimenhydrinate is indicated for the prevention and treatment of nausea, vomiting, or vertigo of motion sickness. It has a short duration of action of 4-8 hours. Patients should be counselled regarding pronounced drowsiness, avoiding alcohol and other sedatives, and exercising caution when operating a motor vehicle or heavy machinery.