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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.
diphenhydrAMINEoral, parenteral (dye-fen-hye-dra-meen) ,
Allergy Formula(trade name),
Benadryl Dye-Free Alergy(trade name),
Benadryl Allergy(trade name),
Compoz Nighttime Sleep Aid(trade name),
Dimetane Allergy(trade name),
Diphen AF(trade name),
Diphen Cough(trade name),
40 Winks(trade name),
Maximum Strength Nytol(trade name),
Maximum Strength Sleepinal(trade name),
Midol PM(trade name),
Miles Nervine(trade name),
Nighttime Sleep Aid(trade name),
Scot-Tussin Allergy DM(trade name),
Sleep-Eze 3(trade name),
Sleepwell 2-night(trade name),
Snooze Fast(trade name),
Unisom Nighttime Sleep-Aid(trade name)
ClassificationTherapeutic: allergy cold cough remedies
- Seasonal and perennial allergic rhinitis,
- Allergic dermatoses.
Time/action profile (antihistaminic effects)
|PO||15–60 min||2–4 hr||4–8 hr|
|IM||20–30 min||2–4 hr||4–8 hr|
Adverse Reactions/Side Effects
Central nervous system
- drowsiness (most frequent)
- paradoxical excitation (increased in children)
Ear, Eye, Nose, Throat
- blurred vision
- anorexia (most frequent)
- dry mouth (most frequent)
- urinary retention
- chest tightness
- thickened bronchial secretions
- 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.
Availability (generic available)
- 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(Indications)
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.
- 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.
- 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.
- 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.
methapyrileneAn 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.
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