Calm-X, Dimenhydrinate Injection
Classifications: antihistamine (h1-receptor antagonist); antiemetic; antivertigo;
Therapeutic: antihistamine
; antiemetic; antivertigo
Prototype: Diphenhydramine
Pregnancy Category: B


50 mg tablets; 50 mg/mL injection; 15.62 mg/5 mL, 12.5 mg/4 mL, 12.5 mg/5 mL liquid


H1-receptor antagonist and salt of diphenhydramine, with which it shares similar properties. Precise mode of antiemetic action is thought to involve ability to inhibit cholinergic stimulation in vestibular and associated neural pathways. It has been reported to inhibit labyrinthine stimulation for up to 3 h.

Therapeutic Effect

Has antihistamine, antiemetic, and antivertigo activity.


Chiefly in prevention and treatment of motion sickness. Also has been used in management of vertigo, nausea, and vomiting associated with radiation sickness, labyrinthitis, M?nière's syndrome, stapedectomy, anesthesia, and various medications.


Narrow-angle glaucoma, BPH; GI obstruction; urinary tract obstruction; CNS depression; lactation, neonates. Safe use in children <2 y is not established.

Cautious Use

Convulsive disorders; asthma, COPD; severe hepatic disease; PKU; history of porphyria; closed-angle glaucoma; elderly; pregnancy (category B).

Route & Dosage

Motion Sickness
Adult: PO 50–100 mg q4–6h (max: 400 mg/24 h) IV/IM 50 mg as needed
Child: PO 2–6 y, up to 25 mg q6–8h (max: 75 mg/24 h); 6–12 y, 25–50 mg q6–8h (max:150 mg/24 h) IM 1.25 mg/kg q.i.d. up to 300 mg/d


  • Note: Give 30–60 min before treatment, then repeat 90 min after treatment, and again in 3 h to prevent radiation sickness.
  • Give undiluted and inject deep IM into a large muscle.

PREPARE: Direct: Dilute each 50 mg in 10 mL of NS.  

ADMINISTER: Direct: Give each 50 mg or fraction thereof over 2 min.  

INCOMPATIBILITIES Solution/additive: Aminophylline, amobarbital, chlorpromazine, glycopyrrolate, hydrocortisone, hydroxyzine, pentobarbital, phenobarbital, phenytoin, prochlorperazine, promazine, promethazine, thiopental.

  • Store preferably at 15°–30° C (59°–86° F), unless otherwise directed by manufacturer.
  • Examine parenteral preparation for particulate matter and discoloration. Do not use unless absolutely clear.

Adverse Effects (≥1%)

CNS: Drowsiness, headache, incoordination, dizziness, blurred vision, nervousness, restlessness, insomnia (especially children). CV: Hypotension, palpitation. GI: Dry mouth, nose, throat; anorexia, constipation or diarrhea. Urogenital: Urinary frequency, dysuria.

Diagnostic Test Interference

Skin testing procedures should not be performed within 72 h after use of an antihistamine.


Drug: Alcohol and other cns depressants enhance CNS depression, drowsiness; tricyclic antidepressants compound anticholinergic effects.


Absorption: Readily absorbed from GI tract. Onset: 15–30 min PO; immediate IV; 20–30 min IM. Duration: 3–6 h. Distribution: Distributed into breast milk. Elimination: In urine.

Nursing Implications

Assessment & Drug Effects

  • Use side rails and supervise ambulation; drug produces high incidence of drowsiness.
  • Note: Tolerance to CNS depressant effects usually occurs after a few days of drug therapy; some decrease in antiemetic action may result with prolonged use.
  • Monitor for dizziness, nausea, and vomiting; these may indicate drug toxicity.

Patient & Family Education

  • Do not drive or engage in other potentially hazardous activities until response to drug is known.
  • Take 30 min before departure to prevent motion sickness; repeat before meals and upon retiring.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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