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Drugs reference index «Diphenhydramine Hydrochloride»

Diphenhydramine Hydrochloride
Diphenhydramine Hydrochloride

Diphenhydramine Hydrochloride

Pronunciation: (die-fen-HIGH-druh-meen HIGH-droe-KLOR-ide)Class: Narcotic antitussive, Anticholinergic, Nonselective ethanolamine

Trade Names:40 Winks- Tablets 50 mg

Trade Names:AllerMax Maximum Strength- Tablets 50 mg

Trade Names:AllerMax- Liquid 12.5 mg per 5 mL

Trade Names:Banophen- Tablets 25 mg- Capsules 25 mg

Trade Names:Banophen Allergy- Elixir 12.5 mg per 5 mL

Trade Names:Benadryl Allergy- Capsules, soft-gels 25 mg- Tablets 25 mg- Tablets, chewable 12.5 mg

Trade Names:Benadryl Children's Allergy- Liquid 12.5 mg per 5 mL

Trade Names:Benadryl Children's Dye-Free- Liquid 12.5 mg per 5 mL

Trade Names:Benadryl Dye-Free Allergy Liquid Gels- Capsules, soft gels 25 mg

Trade Names:Compoz Gel Caps- Capsules 25 mg

Trade Names:Compoz Nighttime Sleep Aid- Tablets 50 mg

Trade Names:Diphen AF- Liquid 12.5 mg per 5 mL

Trade Names:Diphenhist- Solution 12.5 mg per 5 mL

Trade Names:Diphenhist Captabs- Tablets 25 mg

Trade Names:Diphenhydramine- Injection 50 mg/mL

Trade Names:Dormin- Tablets 25 mg- Capsules 25 mg

Trade Names:Genahist- Tablets 25 mg- Capsules 25 mg- Liquid 12.5 mg per 5 mL

Trade Names:Hydramine Cough- Syrup 12.5 mg per 5 mL

Trade Names:Hyrexin-50- Injection 50 mg/mL

Trade Names:Maximum Strength Nytol- Tablets 50 mg

Trade Names:Maximum Strength Sleepinal Capsules and Soft Gels- Capsules 50 mg

Trade Names:Maximum Strength Unisom SleepGels- Capsules 50 mg/mL

Trade Names:Midol PM- Tablets 50 mg

Trade Names:Miles Nervine- Tablets 25 mg

Trade Names:Nytol- Tablets 25 mg

Trade Names:Scot-Tussin Allergy- Liquid 12.5 mg per 5 mL

Trade Names:Siladryl- Elixir 12.5 mg per 5 mL

Trade Names:Simply Sleep- Tablets 25 mg

Trade Names:Sleep-Eze 3- Tablets 25 mg

Trade Names:Sleepwell 2-nite- Tablets 25 mg

Trade Names:Snoozefast- Tablets 50 mg

Trade Names:Sominex- Tablets 25 mg- Tablets 50 mg

Trade Names:Sylphen Cough- Syrup 12.5 mg per 5 mL

Trade Names:Theraflu Thin Strips Multisymptom- Strips, orally disintegrating 25 mg

Trade Names:Triaminic Thin Strips Cough and Runny Nose- Strips, orally disintegrating 12.5 mg

Trade Names:Tusstat- Syrup 12.5 mg per 5 mL

Trade Names:Twilite- Tablets 50 mg

Trade Names:Unisom SleepMelts- Tablets, orally disintegrating 25 mg

Allerdryl (Canada)Allernix (Canada)Nytol Extra Strength (Canada)Simply Sleep (Canada)Unisom Extra Strength (Canada)Unisom Extra Strength Sleepgels (Canada)


Competitively antagonizes histamine at H 1 receptor sites.



T max is 1 to 4 h (oral).


Widely distributed, including the CNS. Excreted in breast milk. 98% to 99% protein bound.


Metabolized in the liver.


A portion of the drug excreted unchanged in the urine. The t ½ is 1 to 4 h.


Rapid onset (IV or IM).


6 to 8 h.

Indications and Usage

Symptomatic relief of perennial and seasonal allergic rhinitis, vasomotor rhinitis and allergic conjunctivitis; temporary relief of runny nose and sneezing caused by common cold; dermatographism; treatment of urticaria and angioedema; amelioration of allergic reactions to blood or plasma; adjunct to epinephrine and other standard measures in anaphylaxis; relief of uncomplicated allergic conditions of immediate type when oral therapy is impossible or contraindicated (parenteral form); treatment and prophylactic treatment of motion sickness (injection only); nighttime sleep aid; management of parkinsonism (including drug-induced) in elderly who are intolerant of more potent agents, in mild cases in other age groups and in combination with centrally acting anticholinergics; control of cough from colds or allergy (syrup formulations).


Hypersensitivity to antihistamines; asthmatic attack; MAO inhibitor therapy; history of sleep apnea; use in newborn or premature infants and in nursing women; use as a local anesthetic.

Dosage and Administration

Cough Suppressant (Syrup)Adults

PO 25 mg every 4 h (max, 150 mg per 24 h).

Children (6 to 12 yr of age)

PO 12.5 mg every 4 h (max, 75 mg per 24 h).

Children (2 to 6 yr of age)

PO 6.25 mg every 4 h (max, 25 mg per 24 h).

Hypersensitivity Reactions, Type 1/Antiparkinsonism/Motion SicknessAdults

PO 25 to 50 mg every 4 to 6 h (max, 300 mg/day). IV/IM 10 to 50 mg IV at a rate not exceeding 25 mg/min or 100 mg deep IM if required (max, 400 mg/day).

Children (6 to younger than 12 yr of age)

PO 12.5 to 25 mg every 4 to 6 h (max, 150 mg). IV/IM 5 mg/kg/day or 150 mg/m 2 /day (max, 300 mg divided into 4 doses at a rate not exceeding 25 mg/min or deep IM).

Nighttime Sleep AidAdults

PO 50 mg at bedtime.

General Advice

  • Chewable tablets and orally-disintegrating tablets
  • Contains phenylalanine. Use caution if administering orally-disintegrating tablet or chewable tablet to patient with phenylketonuria.
  • Provide small amount of water or juice after administering chewable tablet or orally-disintegrating tablet.
  • Allow orally disintegrating tablets to dissolve in mouth or chew before swallowing.
  • Injection
  • For IV or IM administration only.
  • Do not administer if particulate matter, cloudiness, or discoloration noted.
  • Administer IV dose at rate not exceeding 25 mg/min.
  • Administer IM dose via deep IM injection.


Store all dose forms at controlled room temperature (59° to 86°F). Protect injection from freezing and light.

Drug Interactions

Alcohol, CNS depressants

May cause additive CNS depression. Avoid alcoholic drinks.

Beta-blockers metabolized by CYP2D6 enzyme (eg, metoprolol)

Plasma levels may be elevated by diphenhydramine, increasing CV effects.


May increase anticholinergic effects.


Injectable form is incompatible with dexamethasone sodium phosphate, furosemide, iodipamide meglumine, parenteral barbiturates, and phenytoin.

Laboratory Test Interactions

Skin tests

Antihistamines may prevent or diminish otherwise positive reaction to dermal reactivity indicators.

Adverse Reactions


Orthostatic hypotension; palpitations; bradycardia; tachycardia; reflex tachycardia; extrasystoles; faintness.


Drowsiness (often transient); sedation; dizziness; faintness; disturbed coordination.


Nasal stuffiness; dry mouth, nose, and throat; sore throat.


Epigastric distress; nausea; vomiting; diarrhea; constipation; change in bowel habits.


Hemolytic anemia; thrombocytopenia; agranulocytosis.


Increased appetite; weight gain.


Thickening of bronchial secretions; chest tightness; wheezing; respiratory depression.


Hypersensitivity reactions; photosensitivity.



Monitor patient for dizziness and excessive drowsiness. If noted hold therapy. Use caution when administering diphenhydramine by injection. Inadvertent intradermal or subcutaneous administration may cause tissue necrosis.


Category B .


Excreted in breast milk.


Contraindicated in newborn and premature infants. Overdosage may cause hallucinations, convulsions, and death. Antihistamines may diminish mental alertness. In young children, drug may produce paradoxical excitation. Use with caution in children younger than 2 yr of age. Do not use as a nighttime sleep aid in children younger than 12 years of age.


Greater risk of dizziness, excessive sedation, syncope, toxic confusional states, and hypotension in patients older than 60 yr of age. Dosage reduction may be required.


May occur. Have epinephrine 1:1,000 immediately available.

Hepatic Function

Use with caution in patients with cirrhosis or other liver diseases.

Special Risk Patients

Use with caution in patients predisposed to urinary retention, prostatic hypertrophy, history of bronchial asthma, increased IOP, hyperthyroidism, CV disease, or hypertension. Use with considerable caution in patients with narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, symptomatic prostatic hypertrophy, or bladder neck obstruction.

Sulfite Sensitivity

Some diphenhydramine products may contain sulfites as preservatives and aspartame as sweetener. Avoid in sulfite-allergic patients and in patients with phenylketonuria, respectively.

Respiratory disease

Generally not recommended to treat lower respiratory tract symptoms, including asthma.



Circulatory collapse; cardiac arrest; respiratory depression or arrest; toxic psychosis; coma; stupor; seizures; ataxia; anxiety; incoherence; hyperactivity; combativeness; anhidrosis; fever; hot, dry, or flushed skin; dry mucous membranes; dysphagia; decreased bowel sounds; dilated and sluggish pupils.

Patient Information

  • Caution patient using OTC product to read package label before using and not to exceed dose or frequency of administration instructions.
  • Advise patient to take each dose without regard to meals but to take with food if stomach upset occurs.
  • Advise patient using diphenhydramine to prevent motion sickness to take first dose at least 30 min before exposure to motion and take subsequent doses after each meal and at bedtime for duration of journey.
  • Advise patient using diphenhydramine as a sleep aid to take dose at least 30 min before bedtime and not to use for more than 2 wk. Caution patient that if insomnia persists for more than 2 wk, it may be a symptom of a serious underlying illness and to inform health care provider.
  • Advise patient or caregiver using liquid, oral solution, elixir, or syrup to measure and administer prescribed dose using dosing syringe, dosing spoon, or dosing cup.
  • Advise patient that if a dose is missed to take it as soon as possible unless it is nearing time for the next scheduled dose, then advise patient to skip the missed dose and take the next dose at the regularly scheduled time. Caution patient not to double the dose to catch up.
  • Advise patient that if allergy symptoms are not controlled not to increase the dose of medication or frequency of use but to inform their health care provider. Caution patient that larger doses or more frequent dosing does not increase effectiveness and may cause excessive drowsiness or other side effects.
  • Instruct patient to stop taking drug and immediately report any of these symptoms to health care provider: persistent dizziness; excessive drowsiness; severe dry mouth, nose, or throat; flushing; unexplained shortness of breath or difficulty breathing; unusual tiredness or weakness; sore throat, fever, or other signs of infection; bleeding or unusual bruising; fast or irregular heartbeat; excitability, confusion, or changes in thinking or behavior; chest tightness; difficulty urinating.
  • Advise patient that medication may cause drowsiness or dizziness and not to drive or perform other activities requiring mental alertness until tolerance is determined.
  • Advise patient to take sips of water, suck on ice chips or sugarless hard candy, or chew sugarless gum if dry mouth occurs.
  • Caution patient that alcohol and other CNS depressants (eg, sedatives) will have additional sedative effects if taken with diphenhydramine.
  • Caution patient not to take any OTC antihistamines or any other product containing diphenhydramine, including topical products, while taking this medication unless advised by health care provider.
  • Caution patient that medication may cause sensitivity to sunlight and to avoid excessive exposure to the sun or UV light (eg, tanning booths) and to wear protective clothing and use sunscreens until tolerance is determined.
  • If patient is to have allergy skin testing, advise patient not to take the medication for at least 4 days before the skin testing.
  • Injection
  • Advise patient or caregiver that injection is used when it is impractical to take diphenhydramine by mouth and that the medication will be prepared and administered by a health care professional in a medical setting.

Copyright © 2009 Wolters Kluwer Health.

  • Banophen MedFacts Consumer Leaflet (Wolters Kluwer)
  • Ben-Tann Suspension MedFacts Consumer Leaflet (Wolters Kluwer)
  • Benadryl Consumer Overview
  • Benadryl Cream MedFacts Consumer Leaflet (Wolters Kluwer)
  • Benadryl Allergy Chewable Tablets MedFacts Consumer Leaflet (Wolters Kluwer)
  • Diphen Advanced Consumer (Micromedex) - Includes Dosage Information
  • Diphenhydramine Prescribing Information (FDA)
  • Diphenhydramine MedFacts Consumer Leaflet (Wolters Kluwer)
  • Dytuss Elixir MedFacts Consumer Leaflet (Wolters Kluwer)
  • Simply Sleep MedFacts Consumer Leaflet (Wolters Kluwer)
  • Sominex MedFacts Consumer Leaflet (Wolters Kluwer)

See Also...

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