diphenhydramine (Benadryl, Benadryl Allergy Dye-Free LiquiGels, Children's Benadryl Allergy, Children's Triaminic Thin Strips Allergy, Alka-Seltzer Plus Allergy, Nytol, PediaCare Children's Allergy, Simply Sleep, Sominex, QlearQuil Nighttime Allergy Relief, Tranquil Nighttime Sleep Aid, Unisom SleepGels, Unisom SleepMelts, ZzzQuil)
Dosing and uses of Benadryl, Nytol (diphenhydramine)
Adult dosage forms and strengths
oral liquid
- 12.5mg/5mL (Benadryl Allergy Childrens, PediaCare Children’s Allergy, Allergy Relief Childrens)
- 50mg/30mL (ZzzQuil)
elixir
- 12.5 mg/5mL (Altaryl)
syrup
- 12.5 mg/5mL (Altaryl, Quenalin, Silphen Cough)
tablet
- 25mg (Benadryl, Nytol, Simply Sleep, Sominex, Simply Allergy, Tetra-Formula Nighttime Sleep)
- 50mg (Aler-Dryl, Nytol Maximum Strength)
capsule
- 25mg (Benadryl Allergy Dye-Free Allergy, Anti-Hist Allergy, Allergy Relief, Diphenhist, Geri-Dryl)
- 50mg (Banophen, Pharbedryl)
tablet, chewable
- 12.5mg (Benadryl Allergy Childrens)
tablet, dispersible
- 25mg (Unisom SleepMelts)
strip
- 12.5mg (Triaminnic Cough/Runny Nose)
injectable solution
- 50mg/mL
Allergic Reaction
25-50 mg PO q6-8hr; not to exceed 300 mg/day
10-50 mg (no more than 100 mg) IV/IM q4-6hr; not to exceed 400 mg/day
Insomnia
50 mg PO 30 minutes before bedtime
Cough
25-50 mg PO q4hr PRN (syrup preferred); not to exceed 150 mg/day
Motion Sickness
Treatment or prophylaxis: 25-50 mg PO q6-8 hr
Alternatively, 10-50 mg/dose for treatment; may use up to 100 mg if needed; not to exceed 400 mg
Parkinsonism
25 mg PO q8hr initially, then 50 mg PO q6hr; not to exceed 300 mg/day
Alternatively, 10-50 mg IV at a rate not to exceed 25 mg/min; not to exceed 400 mg/day; may also administer 100 mg IM required
Pediatric dosage forms and strengths
oral solution
- 12.5mg/5mL (Benadryl Allergy Childrens, PediaCare Children’s Allergy, Allergy Relief Childrens)
- 50mg/30mL (ZzzQuil)
elixir
- 12.5 mg/5mL (Altaryl)
syrup
- 12.5 mg/5mL (Altaryl, Quenalin, Silphen Cough)
tablet
- 25mg (Benadryl, Nytol, Simply Sleep, Sominex, Simply Allergy, Tetra-Formula Nighttime Sleep)
- 50mg (Aler-Dryl, Nytol Maximum Strength)
capsule
- 25mg (Benadryl Allergy Dye-Free Allergy, Anti-Hist, Allergy Relief, Diphenhist, Geri-Dryl)
- 50mg (Banophen, Pharbedryl)
tablet, chewable
- 12.5mg (Benadryl Allergy Childrens)
tablet, dispersible
- 25mg (Unisom SleepMelts)
strip
- 12.5mg (Triaminnic Cough/Runny Nose)
injectable solution
- 50mg/mL
Allergic Reaction
2-6 years: 6.25 mg q4-6hr; not to exceed 37.5 mg/day
6-12 years: 12.5-25 mg PO q4-6hr; not to exceed 150 mg/day
>12 years: 25-50 mg PO q4-6hr; not to exceed 300 mg/day
Occasional Insomnia
< 12 years (off-label): 1 mg/kg; not to exceed 50 mg; 30 min before bedtime
>12 years: 50 mg PO 30 minutes before bedtime
Cough
<12 years: Safety and efficacy not established
>12 years: 25-50 mg PO q4-6hr; not to exceed 300 mg/day
Motion Sickness
Administer 30 min before motion
12.5-25 mg PO q6-8hr or 150 mg/m² ; not to exceed 300 mg/day
Geriatric dosage forms and strengths
Allergic Reaction
25 mg PO/IV/IM q8-12hr; use only for emergency allergic reactions at smallest effective dose
Nonanticholinergic antihistamines should be considered first for treatment of allergic reaction (Beers criteria); use of diphenhydramine in acute treatment of severe allergic reaction may be appropriate
Dystonic Reaction
50 mg IV/IM; may be repeated in 20-30 minutes if necessary
Cough
25 mg PO q8-12hr; avoid in elderly if possible
Motion Sickness
25 mg PO/IV/IM q8-12hr
Dosing Modifications
Advanced age is associated with reduced clearance of drug and greater risk of confusion, dry mouth, constipation, and other anticholinergic effects and toxicity; if used, consider lower doses
In patients with parkinsonism who are unable to tolerate more potent agents, use at lowest effective dose
Benadryl, Nytol (diphenhydramine) adverse (side) effects
Frequency not defined
Sedation
Confusion
Anticholinergic effects
May decrease cognitive function in geriatric patients
Xerostomia
Dry nasal mucosa
Pharyngeal dryness
Thick bronchial sputum
Agranulocytosis
Hemolytic anemia
Thrombocytopenia
Convulsions
Tachycardia
Hypotension
Nervousness
Restlessness
Blurred vision
Palpitations
Constipation
Vertigo
Menstrual irregularities
Euphoria
Anorexia
Urinary retention
Neuritis
Diplopia
Tinnitus
Warnings
Contraindications
Documented hypersensitivity
Lower respiratory tract disease, such as acute asthma (controversial)
Premature infants or neonates
Nursing mothers
Use as local anesthetic
To make child <6 years sleep, when used for self-medication
Cautions
May cause CNS depression, which can impair driving or operating heavy machinery
May potentiate effects of sedatives such as alcohoL
Use caution in patients with angle-closure glaucoma, prostatic hypertrophy, stenosing peptic ulcer, pyloroduodenal obstruction, thyroid dysfunction
Elderly patients: Considered high-risk medication for this age group because it may increase risk of falls and has high incidence of anticholinergic effects; may exacerbate existing lower urinary tract conditions or benign prostatic hyperplasia; use in special situations may be appropriate; not recommended for treatment of insomnia, because tolerance develops and risk of anticholinergic effects increases
Pregnancy and lactation
Pregnancy category: B
Lactation: Drug enters breast milk; contraindicated
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Benadryl, Nytol (diphenhydramine)
Mechanism of action
Histamine H1-receptor antagonist of effector cells in respiratory tract, blood vessels, and GI smooth muscle
Moderate to high anticholinergic and antiemetic properties
Absorption
Bioavailability: PO, 42-62% (drug is well absorbed but undergoes first-pass metabolism)
Onset: 15-30 min
Duration: ≤12 hr (histamine-induced flare suppression); ≤10 hr (histamine-induced wheal suppression)
Peak serum time: 2 hr (PO)
Distribution
Protein bound: 98.5%
Vd: 22 L/kg (Children); 17 L/kg (adults); 14 L/kg (elderly)
Metabolism
Metabolized by liver (first-pass)
Elimination
Half-life: 5 hr (children); 9 hr (adults); 13.5 hr (elderly)
Excretion: Urine (50-75%), mainly as metabolites
Administration
IV Incompatibilities
Additive: Amobarbital, amphotericin B, dexamethasone, sodium phosphate with lorazepam and metoclopramide, iodipamide meglumine, phenytoin, phenobarbital, thiopentaL
Syringe: Diatrizoate meglumine 52% and diatrizoate sodium 8%, diatrizoate sodium, haloperidol, iodipamide meglumine, ioxaglate meglumine 39.3% and ioxaglate sodium 19.6%, pentobarbital, thiopentaL
Y-site: Allopurinol, amphotericin B cholesteryl sulfate, cefepime, foscarnet, furosemide, phenytoin
IV Administration
pH: 5-6
Infuse at rate no higher than 25 mg/min
Check patency of IV and monitor for irritation
Storage
Store at room temperature of 15-30°C (59-86°F); protect from freezing and light
