Benadryl

Ben·a·dryl (bn-drl)

A trademark for a hydrochloride of diphenhydramine.

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Benadryl,

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

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Benadryl [ben´ah-dril]

trademark for preparations of diphenhydramine hydrochloride, an antihistamine.

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Benadryl,

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

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diphenhydramine hydrochloride

Adult Chesty Cough (UK), Aler-Cap, Aler-Dryl, Allerdryl (CA), AllerMax, Banophen, Benadryl, Benadryl Allergy, Benadryl Child Chesty Cough (UK), Benadryl Dye-Free Allergy, Children's Allergy Fastmelt, Compoz Nighttime Sleep Aid, Dreemon (UK), Diphen AF, Diphenhist, Histergan (UK), Hydramine, Genahist, Mandalyn Paedetriac (UK), Paxidorm (UK), PMS-Diphenhydramine (CA), Nightcalm, Nytol, Siladryl, Simply Sleep, Sleep Aid (UK), Sleepeaze (UK), Sominex, 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

Action

Interferes with histamine effects at histamine₁-receptor sites; prevents but doesn't reverse histamine-mediated response. Also possesses CNS depressant and anticholinergic properties.

Availability

Capsules: 25 mg, 50 mg

Elixir: 12.5 mg/5 ml

Injection: 10 mg/ml, 50 mg/ml

Syrup: 12.5 mg/5 ml

Tablets: 25 mg, 50 mg

Tablets (chewable): 12.5 mg, 25 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.

➣ Cough

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

Contraindications

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

Precautions

Use cautiously in:
• severe hepatic disease, angle-closure glaucoma, seizure disorders, prostatic hypertrophy
• elderly patients
• pregnant patients (safety not established).

Administration

• For motion sickness, administer 30 minutes before activity.
• Give oral doses with food or milk to minimize adverse GI effects.
• 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.

Route	Onset	Peak	Duration
P.O.	15-60 min	1-4 hr	4-8 hr
I.V.	Rapid	Unknown	4-8 hr
I.M.	20-30 min	1-4 hr	4-8 hr

Adverse reactions

CNS: drowsiness, dizziness, headache, paradoxical stimulation (especially in children)

CV: hypotension, palpitations

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

Interactions

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 take drug with food if it causes GI upset.
• 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.

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Benadryl®

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