dimenhydrinate
Apo-Dimenhydrinate ◆, Calm-X, Dimetabs, Dinate, Dommanate, Dramamine, Dramocen, Dramoject, Dymenate, Gravol ◆, Hydrate, PMS-Dimenhydrinate ◆, Triptone

Available forms
Available with or without a prescription
Injection: 50 mg/ml
Solution: 12.5 mg/5 ml, 12.5 mg/4 ml, 15.62 mg/5 ml
Tablets: 50 mg
Tablets (chewable): 50 mg
Tablets (film-coated): 50 mg

Indications and dosages
 Prophylaxis and treatment of nausea, vomiting, dizziness from motion sickness. Adults and children age 12 and older: 50 to 100 mg q 4 to 6 hours P.O., I.V., or I.M. For I.V. administration, dilute each 50-mg dose in 10 ml of normal saline solution and inject slowly over 2 minutes.
Children: 1.25 mg/kg daily or 37.5 mg/m² daily P.O. or I.M. q.i.d. not to exceed 300 mg daily, or as follows:
Children ages 6 to 12: 25 to 50 mg P.O. q 6 to 8 hours. Maximum, 150 mg daily.
Children ages 2 to 6: 12.5 to 25 mg P.O. q 6 to 8 hours. Maximum, 75 mg daily.
 Meniere’s disease ◇. Adults: 50 mg I.M. for acute attack. Maintenance dose is 25 to 50 mg P.O. t.i.d.

Pharmacodynamics
Antiemetic and antivertigo actions: Dimenhydrinate probably inhibits nausea and vomiting by centrally depressing sensitivity of the labyrinth apparatus that relays stimuli to the chemoreceptor trigger zone and stimulates the vomiting center in the brain.
Antihistaminic action: Drug is believed to inhibit histamine release.

Pharmacokinetics
Absorption: Well absorbed.
Distribution: Well distributed throughout the body and crosses the placental barrier.
Metabolism: Metabolized in the liver.
Excretion: Metabolites are excreted in urine.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug or its components. The I.V. product contains benzyl alcohol, which has been linked to a fatal "gasping syndrome" in premature infants and low-birth-weight infants. Use cautiously in patients receiving ototoxic drugs and those with seizures, acute angle-closure glaucoma, or an enlarged prostate gland.

Interactions
Drug-drug. Aminoglycosides, cisplatin, loop diuretics, salicylates, vancomycin: May mask signs of ototoxicity, which can be caused by these drugs. Monitor patient closely.
CNS depressants, such as anxiolytics, barbiturates, sleeping agents, and tranquilizers: Causes additive CNS sedation and depression. Avoid use together.
Drug-lifestyle. Alcohol use: May cause additive CNS depression. Discourage alcohol use.

Adverse reactions
CNS: drowsiness, headache, dizziness, confusion, nervousness, insomnia, vertigo, tingling and weakness of hands, lassitude, excitation.
CV: palpitations, hypotension, tachycardia, tightness of chest.
EENT: blurred vision, dry respiratory passages, diplopia, nasal congestion.
GI: dry mouth, nausea, vomiting, diarrhea, epigastric distress, constipation, anorexia.
Respiratory: wheezing, thickened bronchial secretions.
Skin: photosensitivity, urticaria, rash.
Other: anaphylaxis.

Effects on lab test results
None reported.

Overdose and treatment
Signs and symptoms of overdose may include either CNS depression (sedation, reduced mental alertness, apnea, and CV collapse) or CNS stimulation (insomnia, hallucinations, tremors, or seizures). Anticholinergic symptoms, such as dry mouth, flushed skin, fixed and dilated pupils, and GI symptoms, are likely to occur, especially in children.
 Use gastric lavage to empty stomach contents; emetics may be ineffective. Diazepam or phenytoin may be used to control seizures. Provide supportive treatment.

Special considerations
 ALERT Most I.V. products contain benzyl alcohol, which has been linked to a fatal "gasping syndrome" in premature infants and low-birth-weight infants.
• Chewable tablets contain tartrazine, which may cause allergy-like reactions in some patients. This is frequently seen in patients who also have an aspirin hypersensitivity.
• Incorrectly administered or undiluted I.V. solution is irritating to veins and may cause sclerosis.
• Parenteral solution is incompatible with many drugs; don’t mix other drugs in the same syringe.
• Antiemetic effect may diminish with prolonged use.
• Dimenhydrinate may alter or confuse test results for xanthines (caffeine, aminophylline) because of its 8-chlorotheophylline content; discontinue dimenhydrinate 4 days before diagnostic skin tests to avoid preventing, reducing, or masking test response.
Breast-feeding patients
• Many antihistamines appear in breast milk, exposing infant to risks of unusual excitability; premature infants are at particular risk for seizures. Avoid use of antihistamines in breast-feeding women.
Pediatric patients
• Safety in neonates hasn’t been established. Infants and children younger than age 6 may experience paradoxical hyperexcitability. I.V. dosage for children hasn’t been established.
Geriatric patients
• Elderly patients are usually more sensitive to adverse effects of antihistamines than younger patients and are especially likely to experience a greater degree of dizziness, sedation, hyperexcitability, dry mouth, and urine retention.

Patient education
• Tell patient to avoid hazardous activities, such as driving or operating heavy machinery, until adverse CNS effects of drug are known.
• To prevent motion sickness, patient should take drug 30 minutes before traveling and again before meals and at bedtime.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use