diphenhydramine hydrochloride(redirected from Diphenhist)
Also found in: Dictionary, Thesaurus.
Pharmacologic class: Ethanolamine derivative, nonselective histamine1-receptor antagonist
Therapeutic class: Antihistamine, antitussive, antiemetic, antivertigo agent, antidyskinetic
Pregnancy risk category B
Interferes with histamine effects at histamine1-receptor sites; prevents but doesn't reverse histamine-mediated response. Also possesses CNS depressant and anticholinergic properties.
Capsules: 25 mg, 50 mg
Elixir: 12.5 mg/5 ml
Injection: 10 mg/ml, 50 mg/ml
Strips (orally disintegrating): 12.5 mg, 25 mg
Syrup: 12.5 mg/5 ml
Tablets: 25 mg, 50 mg
Tablets (chewable): 12.5 mg, 25 mg
Tablets (orally disintegrating): 12.5 mg
Indications and dosages
➣ Allergy symptoms caused by histamine release (including anaphylaxis, seasonal and perennial allergic rhinitis, and allergic dermatoses); nausea; vertigo
Adults and children over age 12: 25 to 50 mg P.O. q 4 to 6 hours, or 10 to 50 mg I.V. or I.M. q 2 to 3 hours p.r.n. (Some patients may need up to 100 mg.) Don't exceed 400 mg/day.
Children ages 6 to 12: 12.5 to 25 mg P.O. q 4 to 6 hours, or 1.25 mg/kg (37.5 mg/m2) I.M. or I.V. q.i.d. Don't exceed 150 mg/day.
Children ages 2 to 5: 6.25 mg P.O. q 4 to 6 hours. Don't exceed 37.5 mg/day.
Adults: 25 mg P.O. q 4 hours p.r.n. Don't exceed 150 mg/day.
Children ages 6 to 12: 12.5 mg P.O. q 4 hours. Don't exceed 75 mg/day.
Children ages 2 to 5: 6.25 mg P.O. q 4 hours. Don't exceed 37.5 mg/24 hours.
➣ Dyskinesia; Parkinson's disease
Adults: Initially, 25 mg P.O. t.i.d.; may be increased to a maximum of 50 mg q.i.d.
➣ Mild nighttime sedation
Adults: 50 mg P.O. 20 to 30 minutes before bedtime
• Elderly patients
• Drug-induced extrapyramidal reactions
• Hypersensitivity to drug
• Alcohol intolerance
• Acute asthma attacks
• MAO inhibitor use within past 14 days
• Neonates, premature infants
Use cautiously in:
• severe hepatic disease, angle-closure glaucoma, seizure disorders, prostatic hypertrophy, cardiovascular disease, hyperthyroidism
• elderly patients
• pregnant patients (safety not established)
• children younger than age 2 (safety not established).
• For motion sickness, administer 30 minutes before activity.
• For I.V. use, check compatibility before mixing with other drugs.
• Inject I.M. dose deep into large muscle mass; rotate sites.
• Discontinue drug 4 days before allergy skin testing to avoid misleading results.
☞ Don't give within 14 days of MAO inhibitors.
CNS: drowsiness, dizziness, headache, paradoxical stimulation (especially in children)
CV: hypotension, palpitations, tachycardia
EENT: blurred vision, tinnitus
GI: diarrhea, constipation, dry mouth
GU: dysuria, urinary frequency or retention
Other: decreased appetite, pain at I.M. injection site
Drug-drug. Antihistamines, opioids, sedative-hypnotics: additive CNS depression
Disopyramide, quinidine, tricyclic antidepressants: increased anticholinergic effects
MAO inhibitors: intensified and prolonged anticholinergic effects
Drug-diagnostic tests. Skin allergy tests: false-negative results
Hemoglobin, platelets: decreased values
Drug-herbs. Angel's trumpet, jimson weed, scopolia: increased anticholinergic effects
Chamomile, hops, kava, skullcap, valerian: increased CNS depression
Drug-behaviors. Alcohol use: increased CNS depression
• Monitor cardiovascular status, especially in patients with cardiovascular disease.
• Supervise patient during ambulation. Use side rails as necessary.
• Advise patient to avoid alcohol and other depressants such as sedatives while taking drug.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.