diphenhydrAMINE (oral, parenteral) (dye-fen-hye-dra-meen) Aller-Aide, Allerdryl, Allergy Formula, AllerMax, Allernix, Banophen, Benadryl Dye- Free Alergy, Benadryl Allergy, Benadryl, Benylin, Calmex, Compoz, Compoz Nighttime Sleep Aid, 442 diphenhydrAMINE Dimetane Allergy, Diphen AF, Diphen Cough, Diphenhist, Dormex, Dormiphen, Genahist, 40 Winks, Hyrexin- 50, Insomnal, Maximum Strength Nytol, Maximum Strength Sleepinal, Midol PM, Miles Nervine, Nadryl, Nighttime Sleep Aid, Nytol, Scot-Tussin Allergy DM, Siladril, Silphen, Sleep-Eze 3, Sleepwell 2-night, Sominex, Snooze Fast, Sominex, Tusstat, Twilite, Unisom Nighttime Sleep- Aid

 Indications

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).

Action

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.

Pharmacokinetics

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)

ROUTE ONSET PEAK DURATION

PO 15–60 min 2–4 hr 4–8 hr

IM 20–30 min 2–4 hr 4–8 hr

IV rapid unknown 4–8 hr

Contraindications/Precautions

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; OB: Safety not established;

Geri: 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); dosepor nonanticholinergic

antihistamine recommended.

Adverse Reactions/Side Effects

CNS: drowsiness, dizziness, headache, paradoxical excitation

(increased in children). EENT: blurred vision,

tinnitus. CV: hypotension, palpitations. GI: anorexia,

dry mouth, constipation, nausea. GU: dysuria,

frequency, urinary retention. Derm: photosensitivity.

Resp: chest tightness, thickened bronchial secretions,

wheezing. Local: pain at IM site.

Interactions

Drug-Drug:qrisk of CNS depression with other antihistamines,

alcohol, opioid analgesics, and sedative/

hypnotics.qanticholinergic effects with tricyclic

antidepressants, quinidine, or

disopyramide. MAO inhibitors intensify and prolong

the anticholinergic effects of antihistamines.

Drug-Natural Products: Concomitant use of

kava-kava, valerian, or chamomile canqCNS depression.

Route/Dosage

PO (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.

PO (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).

PO (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).

IM, IV (Adults): 25–50 mg q 4 hr as needed (may

need up to 100-mg dose, not to exceed 400 mg/day).

IM, IV (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, 50mgRx, OTC. Tablets: 12.5

mgRx, OTC, 25mgRx, OTC, 50mgRx, OTC. Chewable tablets (grape flavor): 25 mgRx, OTC. Orally disintegrating

strips (cherry and grape flavor): 12.5 mgRx, OTC, 25

mgOTC. Orally disintegrating tablets: 12.5 mgOTC, 25

mgOTC, 50mgRx, OTC. Elixir (cherry and other flavors):

12.5 mg/5 mLRx, OTC. Syrup (cherry 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 Appendix B.