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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.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


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Therapeutic: allergy cold cough remedies
Pregnancy Category: B


Relief of allergic symptoms caused by histamine release including:
  • Anaphylaxis,
  • Seasonal and perennial allergic rhinitis,
  • Allergic dermatoses.
Parkinson's disease and dystonic reactions from medications.Mild nighttime sedation.Prevention of motion sickness.Antitussive (syrup only).


Antagonizes the effects of histamine at H1-receptor sites; does not bind to or inactivate histamine.
Significant CNS depressant and anticholinergic properties.

Therapeutic effects

Decreased symptoms of histamine excess (sneezing, rhinorrhea, nasal and ocular pruritus, ocular tearing and redness, urticaria).
Relief of acute dystonic reactions.
Prevention of motion sickness.
Suppression of cough.


Absorption: Well absorbed after oral or IM administration but 40–60% of an oral dose reaches systemic circulation due to first-pass metabolism.
Distribution: Widely distributed. Crosses the placenta; enters breast milk.
Metabolism and Excretion: 95% metabolized by the liver.
Half-life: 2.4–7 hr.

Time/action profile (antihistaminic effects)

PO15–60 min2–4 hr4–8 hr
IM20–30 min2–4 hr4–8 hr
IVrapidunknown4–8 hr


Contraindicated in: Hypersensitivity;Acute attacks of asthma; Lactation: Lactation;Known alcohol intolerance (some liquid products).
Use Cautiously in: Severe liver disease;Angle-closure glaucoma;Seizure disorders;Prostatic hyperplasia;Peptic ulcer;May cause paradoxical excitation in young children;Hyperthyroidism; Obstetric: Safety not established; Geriatric: Appears on Beers list. Geriatric patients are more susceptible to adverse drug reactions and anticholinergic effects (delirium, acute confusion, dizziness, dry mouth, blurred vision, urinary retention, constipation, tachycardia); dose ↓ or nonanticholinergic antihistamine recommended.

Adverse Reactions/Side Effects

Central nervous system

  • drowsiness (most frequent)
  • dizziness
  • headache
  • paradoxical excitation (increased in children)

Ear, Eye, Nose, Throat

  • blurred vision
  • tinnitus


  • hypotension
  • palpitations


  • anorexia (most frequent)
  • dry mouth (most frequent)
  • constipation
  • nausea


  • dysuria
  • frequency
  • urinary retention


  • photosensitivity


  • chest tightness
  • thickened bronchial secretions
  • wheezing


  • pain at IM site


Drug-Drug interaction

↑ risk of CNS depression with other antihistamines, alcohol, opioid analgesics, and sedative/hypnotics.↑ anticholinergic effects with tricyclic antidepressants, quinidine, or disopyramide.MAO inhibitors intensify and prolong the anticholinergic effects of antihistamines.Concomitant use of kava-kava, valerian, or chamomile can ↑ CNS depression.


Oral (Adults and Children >12 yr) Antihistaminic/antiemetic/antivertiginic—25–50 mg q 4–6 hr, not to exceed 300 mg/day. Antitussive—25 mg q 4 hr as needed, not to exceed 150 mg/day. Antidyskinetic—25–50 mg q 4 hr (not to exceed 400 mg/day). Sedative/hypnotic—50 mg 20–30 min before bedtime.
Oral (Children 6–12 yr) Antihistaminic/antiemetic/antivertiginic—12.5–25 mg q 4–6 hr (not to exceed 150 mg/day). Antidyskinetic—1–1.5 mg/kg q 6–8 hr as needed (not to exceed 300 mg/day). Antitussive—12.5 mg q 4 hr (not to exceed 75 mg/day). Sedative/hypnotic—1 mg/kg/dose 20–30 min before bedtime (not to exceed 50 mg).
Oral (Children 2–6 yr) Antihistaminic/antiemetic/antivertiginic—6.25–12.5 mg q 4–6 hr (not to exceed 37.5 mg/day). Antidyskinetic—1–1.5 mg/kg q 4–6 hr as needed (not to exceed 300 mg/day). Antitussive—6.25 mg q 4 hr (not to exceed 37.5 mg/24 hr). Sedative/hypnotic—1 mg/kg/dose 20–30 min before bedtime (not to exceed 50 mg).
Intramuscular Intravenous (Adults) 25–50 mg q 4 hr as needed (may need up to 100-mg dose, not to exceed 400 mg/day).
Intramuscular Intravenous (Children) 1.25 mg/kg (37.5 mg/m2) 4 times daily (not to exceed 300 mg/day).
Topical (Adults and Children ≥2 yr) Apply to affected area up to 3–4 times daily.

Availability (generic available)

Capsules: 25 mgRx, OTC, 50 mgRx, OTC
Tablets: 12.5 mgRx, OTC, 25 mgRx, OTC, 50 mgRx, OTC
Chewable tabletsgrape flavor: 25 mgRx, OTC
Orally disintegrating stripscherry and grape flavor: 12.5 mgRx, OTC, 25 mgOTC
Orally disintegrating tablets: 12.5 mgOTC, 25 mgOTC, 50 mgRx, OTC
Elixircherry and other flavors: 12.5 mg/5 mLRx, OTC
Syrupcherry and raspberry flavor: 6.25 mg/5 mLRx, OTC, 12.5 mg/5 mLRx, OTC
Cream: 1%Rx, OTC, 2%Rx, OTC
Topical gel: 2%OTC
Topical spray: 2%OTC
Topical stick: 2%OTC
Injection: 50 mg/mL
In combination with: analgesics, decongestants, and expectorants, in OTC pain, sleep, cough, and cold preparations. See combination drugs.

Nursing implications

Nursing assessment

  • Diphenhydramine has multiple uses. Determine why the medication was ordered and assess symptoms that apply to the individual patient. Geriatric: Appears in the Beers list. May cause sedation and confusion due to increased sensitivity to anticholinergic effects. Monitor carefully, assess for confusion, delirium, other anticholinergic side effects and fall risk. Institute measures to prevent falls.
  • Prevention and Treatment of Anaphylaxis: Assess for urticaria and for patency of airway.
  • Allergic Rhinitis: Assess degree of nasal stuffiness, rhinorrhea, and sneezing.
  • Parkinsonism and Extrapyramidal Reactions: Assess movement disorder before and after administration.
  • Insomnia: Assess sleep patterns.
  • Motion Sickness: Assess nausea, vomiting, bowel sounds, and abdominal pain.
  • Cough Suppressant: Assess frequency and nature of cough, lung sounds, and amount and type of sputum produced. Unless contraindicated, maintain fluid intake of 1500–2000 mL daily to decrease viscosity of bronchial secretions.
  • Pruritus: Assess degree of itching, skin rash, and inflammation.
  • Lab Test Considerations: May ↓ skin response to allergy tests. Discontinue 4 days before skin testing.

Potential Nursing Diagnoses

Risk for deficient fluid volume (Indications)
Risk for injury (Side Effects)


  • Do not confuse Benadryl with benazepril.
    • When used for insomnia, administer 20 min before bedtime and schedule activities to minimize interruption of sleep.
    • When used for prophylaxis of motion sickness, administer at least 30 min and preferably 1–2 hr before exposure to conditions that may precipitate motion sickness.
  • Oral: Administer with meals or milk to minimize GI irritation. Capsule may be emptied and contents taken with water or food.
    • Orally disintegrating tablets and strips should be left in the package until use. Remove from the blister pouch. Do not push tablet through the blister; peel open the blister pack with dry hands and place tablet on tongue. Tablet will dissolve rapidly and be swallowed with saliva. No liquid is needed to take the orally disintegrating tablet.
  • Intramuscular: Administer 50 mg/mL into well-developed muscle. Avoid subcut injections.
  • Intravenous Administration
  • Diluent: May be further diluted in 0.9% NaCl, 0.45% NaCl, D5W, D10W, dextrose/saline combinations, Ringer’s solution, LR, and dextrose/Ringer’s combinations.Concentration: 25 mg/mL.
  • Rate: Infuse at a rate not to exceed 25 mg/min.
  • Y-Site Compatibility: acetaminophen, aldesleukin, alemtuzumab, alfentanil, amifostine, amikacin, aminocaproic acid, amphotericin B lipid complex, amphotericin B liposome, amsacrine, anidulafungin, argatroban, ascorbic acid, atropine, azithromycin, benztropine, bivalirudin, bleomycin, bumetanide, buprenorphine, butorphanol, calcium chloride, calcium gluconate, carboplatin, carmustine, caspofungin, ceftaroline, chlorpromazine, ciprofloxacin, cisatracurium, cisplatin, cladribine, clindamycin, cyanocobalamin, cyclophosphamide, cyclosporine, cytarabine, dactinomycin, daptomycin, dexmedetomidine, dexrazoxane, digoxin, diltiazem, dobutamine, docetaxel, dolasetron, dopamine, doripenem, doxorubicin, doxorubicin liposome, doxycycline, enalaprilat, ephedrine, epinephrine, epirubicin, epoetin alfa, eptifibatide, ertapenem, erythromycin, esmolol, etoposide, etoposide phosphate, famotidine, fenoldopam, fentanyl, filgrastim, fluconazole, fludarabine, folic acid, gemcitabine, gentamicin, glycopyrrolate, granisetron, hydromorphone, idarubicin, ifosfamide, imipenem/cilastatin, iriniotecan, isoproterenol, ketamine, labetalol, leucovorin calcium, levofloxacin, lidocaine, linezolid, lorazepam, magnesium sulfate, mannitol, mechlorethamine, melphalan, meperidine, meropenem, metaraminol, methadone, methotrexate, methyldopate, metoclopramide, metoprolol, metronidazole, midazolam, mitomycin, mitoxantrone, morphine, moxifloxacin, multiple vitamins, mycophenolate, nalbuphine, naloxone, nesiritide, nicardipine, nitroglycerin, norepinephrine, octreotide, ondansetron, oxaliplatin, oxytocin, paclitaxel, palonosetron, pamidronate, papaverine, pemetrexed, penicillin G, pentamidine, pentazocine, phentolamine, phenylephrine, phytonadione, piperacillin/tazobactam, potassium acetate, potassium chloride, procainamide, prochlorperazine, promethazine, propofol, propranolol, protamine, pyridoxime, quinipristin/dalfopristin, ranitidine, remifentanil, rituximab, rocuronium, sargramostim, sodium acetate, streptokinase, succinylcholine, sufentanil, tacrolimus, teniposide, theophylline, thiamine, thiotepa, ticarcillin/clavulanate, tigecycline, tirofiban, tobramycin, tolazoline, trastuzumab, vancomycin, vasopressin, vecuronium, verapamil, vinblastine, vincristine, vinorelbine, vitamin B complex with C, voriconazole, zoledronic acid
  • Y-Site Incompatibility: allopurinol, aminophylline, amphotericin B cholesteryl, amphotericin B colloidal, ampicillin, azathioprine, cefazolin, cefepime, cefoperazone, cefotaxime, cefotetan, cefoxitin, ceftazidime, ceftriaxone, cefuroxime, chloramphenicol, dantrolene, dexamethasone, diazepam, diazoxide, fluorouracil, foscarnet, furosemide, ganciclovir, indomethacin, insulin, ketorolac, methylprednisolone, milrinone, nitroprusside, oxacillin, pantoprazole, pentobarbital, phenobarbital, phenytoin, sodium bicarbonate, trimethoprim/sulfamethoxazole
  • Topical: Apply a thin coat and rub gently until absorbed. Only for topical use; avoid ingestion.

Patient/Family Teaching

  • Instruct patient to take medication as directed; do not exceed recommended amount. Caution patient not to use oral OTC diphenhydramine products with any other product containing diphenhydramine, including products used topically.
    • May cause drowsiness. Caution patient to avoid driving or other activities requiring alertness until response to drug is known.
    • May cause dry mouth. Inform patient that frequent oral rinses, good oral hygiene, and sugarless gum or candy may minimize this effect. Notify health care professional if dry mouth persists for more than 2 wk.
    • Teach sleep hygiene techniques (dark room, quiet, bedtime ritual, limit daytime napping, avoidance of nicotine and caffeine) to patients taking diphenhydramine to aid sleep.
    • Advise patient to use sunscreen and protective clothing to prevent photosensitivity reactions.
    • Caution patient to avoid use of alcohol and other CNS depressants concurrently with this medication.
    • Pediatric: Can cause excitation in children. Caution parents or caregivers about proper dose calculation; overdose, especially in infants and children, can cause hallucinations, seizures, or death. Caution parents to avoid OTC cough and cold products while breast feeding or to children <4 yr.
    • Geriatric: Instruct older adults to avoid OTC products that contain diphenhydramine due to increased sensitivity to anticholinergic effects and potential for adverse reactions related to these effects.
    • Advise patients taking diphenhydramine in OTC preparations to notify health care professional if symptoms worsen or persist for more than 7 days.

Evaluation/Desired Outcomes

  • Prevention of, or decreased urticaria in, anaphylaxis or other allergic reactions.
  • Decreased dyskinesia in parkinsonism and extrapyramidal reactions.
  • Sedation when used as a sedative/hypnotic.
  • Prevention of or decrease in nausea and vomiting caused by motion sickness.
  • Decrease in frequency and intensity of cough without eliminating cough reflex.
Drug Guide, © 2015 Farlex and Partners


A trademark for the drug diphenhydramine hydrochloride.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


An ethylenediamine antihistamine and anticholinergic once used in over-the-counter cold medicine and sleeping aids. It was found to be carcinogenic in rats and removed from the market in 1979.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

Patient discussion about Nytol

Q. Is Nytol Effective and Safe? I have been under excessive stress for the past few days mainly because of my new office. I find the working conditions quite hostile mainly because I have a social anxiety disorder. I do have an individual cabin where I am isolated from others, but it is the break hours that I dread when people get together. I feel completely out of place and often times the butt of all jokes. These thoughts keep hovering in my mind all the time. I am not able to sleep and my mind keeps churning out negative thoughts all night long. Because of this my productivity at work has reduced a lot. Is there any way I can stop my mind from thinking when I go to bed? My friend recommended <a href="http://www.pharmacyfix.co.uk/medicines/sleep-problems/nytol-herbal-tablets.htm">nytol</a> but I am not sure if this would be effective. Please advice..

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