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trademark for preparations of diphenhydramine hydrochloride, an antihistamine.

diphenhydramine hydrochloride

Aler-Cap, Aler-Dryl, Allerdryl (CA), AllerMax, Altaryl, Anti-Hist, Banophen, Benadryl, Benadryl Allergy, Benadryl Child Chesty Cough (UK), Benadryl Children's Allergy Fastmelt, Benadryl Dye-Free Allergy, Benadryl Itch Relief, Compoz Nighttime Sleep Aid, Dermamycin, Diphen, Diphenhist, Dytan, Genahist, Histapryn, Histergan (UK), Hydramine, Mandalyn Paedetriac (UK), Nightcalm, Nytol, PMS-Diphenhydramine (CA), Siladryl, Simply Sleep, Sleepeaze (UK), Sleepettes D, Sleepinal, Sominex, Theraflu Thin Strips Multisymptom, Triaminic Thin Strips Children's Cough and Runny Nose, Twilite, Unisom Maximum Strength SleepGels

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

Dosage adjustment

• Elderly patients

Off-label uses

• Drug-induced extrapyramidal reactions


• Hypersensitivity to drug
• Alcohol intolerance
• Acute asthma attacks
• MAO inhibitor use within past 14 days
• Breastfeeding
• 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.

Adverse reactions

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

Skin: photosensitivity

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

Patient monitoring

• Monitor cardiovascular status, especially in patients with cardiovascular disease.
• Supervise patient during ambulation. Use side rails as necessary.

Patient teaching

• 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.


A trademark for the drug diphenhydramine hydrochloride.


a trademark for a first-generation antihistamine (diphenhydramine hydrochloride).


A proprietary antihistamine developed in the mid-1940s which, like other older sedating agents, has been associated with fatal RTAs/MVAs.
Adverse effects Drowsiness, heartburn, dizziness.


Diphenhydramine Allergy medicine An antihistamine which, like other older sedating agents, has been associated with fatal MVAs. See Antihistamine.


A brand name for DIPHENHYDRAMINE.

Benadryl, brand name for diphenhydramine hydrochloride, an antihistamine with anticholinergic (drying) and sedative side effects.
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