Action And Clinical Pharmacology: Meclizine has antihistaminic and anticholinergic properties. The site and mechanism of action of meclizine in controlling vertigo arising from various conditions, have not been clearly defined. Pharmacological studies conducted with other antihistamines show that the peripheral labyrinthine structures may be the site of action.
Indications And Clinical Uses: For prophylaxis and symptomatic relief of nausea, vomiting and vertigo associated with motion sickness, radiation sickness, labyrinthitis and other vestibular disturbances.
Contra-Indications: In patients with known hypersensitivity to meclizine.
Manufacturers’ Warnings In Clinical States: Occupational Hazards: Patients should be warned that meclizine may occasionally cause drowsiness and that when taking it they should take the necessary precautions against driving or operating dangerous machinery.
Patients suffering from glaucoma or prostatic enlargement should take meclizine only under the direction of a physician.
As with all antihistamines, meclizine may cause hyperexcitability in children.
Precautions: Pregnancy: Epidemiological studies with meclizine in women experiencing nausea and vomiting of pregnancy has revealed no evidence of a teratogenic effect attributable to the drug.
As with many other drugs of this class, certain teratogenic effects have been observed in the rat. In the rat meclizine at doses of 25 to 50 times the human dose has shown certain fetal abnormalities. These abnormalities have not been observed in other experimental animals, including the monkey.
The use of meclizine by women who are pregnant or may become pregnant requires that the potential benefits be weighed against the potential risks.
Drug Interactions: There may be increased CNS depression when meclizine is administered concurrently with other CNS depressants, including barbiturates, alcohol, tranquilizers and sedatives.
MAO inhibitors may prolong and intensify the anticholinergic effects of meclizine.
Adverse Reactions: Drowsiness, dry mouth, fatigue, vomiting and, on rare occasions, blurred vision have been reported with meclizine therapy.
Symptoms And Treatment Of Overdose: Symptoms: In adults, the usual signs of meclizine overdose are CNS depression with drowsiness, coma and convulsions. Hypotension may also occur, particularly in the elderly. In children, anticholinergic effects and CNS stimulation (hallucinations, seizures, trouble sleeping) are more likely to occur.
Treatment: There is no specific antidote for treatment of meclizine overdosage. Symptomatic and supportive treatment should be employed. If ingestion is recent (within 1 hour), induce emesis (syrup of ipecac is recommended; precautions against aspiration are required, especially in infants and children) or empty stomach by gastric lavage if patient has been unable to vomit within 3 hours of ingestion. Activated charcoal may also be used. Keep patient calm to minimize excitation. Vasopressors (norepinephrine or phenylephrine) may be used to correct hypotension. Physostigmine may be useful to counteract the CNS anticholinergic effects of meclizine. Do not use stimulants. If vasopressors are indicated do not use epinephrine, because it may lower blood pressure further. Diazepam i.v. may be given for treatment of seizures that do not respond to physostigmine.
Dosage And Administration: Adults: The recommended dose for specific indications is: Motion Sickness: A single dose of 25 to 50 mg affords protection against motion sickness for approximately 24 hours. The initial dose should be taken at least 1 hour prior to traveling in order to insure absorption of the drug, as retention of the medication is uncertain in individuals who have already developed motion sickness. Thereafter, the dose may be repeated every 24 hours as indicated for the duration of the journey.
Labyrinthine and Vestibular Disturbances: The optimal dosage is usually 25 to 100 mg daily in divided doses, depending on the clinical response.
Radiation Sickness: 50 mg administered 2 to 12 hours prior to radiation treatment.
Children: Children require about one half the adult dose.
The fruit-flavored tablets may be chewed, swallowed whole or allowed to dissolve in the mouth.
Availability And Storage: Each scored, white, fruit-flavored tablet contains: meclizine HCl 25 mg. Nonmedicinal ingredients: microcrystalline cellulose, cornstarch, lactose, magnesium stearate/sodium lauryl sulfate, raspberry flavor and sucrose. Tartrazine-free. Bottles of 100. Store between 15 and 30°C.
BONAMINE Pfizer Meclizine HCl Antiemetic