• 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).

Contraindicated in:

• Hypersensitivity
• Acute attacks of asthma
• Known alcohol intolerance (some liquid products)
• Lactation: Lactation.

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 in pregnancy
• Geri: Appears on Beers list. ↑ risk of anticholinergic adverse reactions in older adults, including falls, delirium, and dementia. Avoid use of oral formulations in older adults.

CV: hypotension, palpitations.

Derm: photosensitivity.

EENT: blurred vision, tinnitus.

GI: anorexia, dry mouth, constipation, nausea.

GU: dysuria, urinary frequency, urinary retention.

Local: pain at IM site.

Neuro: drowsiness, dizziness, headache, paradoxical excitation (↑ in children).

Resp: chest tightness, thickened bronchial secretions, wheezing.

Drug-Drug:

• ↑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.

Drug-Natural Products:

• Concomitant use of kava-kava, valerian, or chamomile can ↑ CNS depression.

(Generic available)

• Capsules: 25 mg^{Rx, OTC}; 50 mg^{Rx, OTC};
• Tablets: 12.5 mg^{Rx, OTC}; 25 mg^{Rx, OTC}; 50 mg^{Rx, OTC};
• Chewable tablets (grape flavor): 25 mg^{Rx, OTC};
• Orally disintegrating strips (cherry and grape flavor): 12.5 mg^{Rx, OTC}; 25 mg^OTC;
• Orally disintegrating tablets: 12.5 mg^OTC; 25 mg^OTC; 50 mg^{Rx, OTC};
• Elixir (cherry and other flavors): 12.5 mg/5 mL^{Rx, OTC};
• Syrup (cherry and raspberry flavor): 6.25 mg/5 mL^{Rx, OTC}; 12.5 mg/5 mL^{Rx, OTC};
• Cream: 1%^{Rx, OTC}; 2%^{Rx, OTC};
• Topical gel: 2%^OTC;
• Topical spray: 2%^OTC;
• Topical stick: 2%^OTC;
• Solution for injection: 50 mg/mL;
• In combination with: analgesics, decongestants, and expectorants, in OTC pain, sleep, cough, and cold preparations. See Appendix [not included in this PDA edition].

• PO (Adults and Children >12 yr): Antihistaminic/antiemetic/antivertiginic: 25–50 mg every 4–6 hr, not to exceed 300 mg/day. Antitussive: 25 mg every 4 hr as needed, not to exceed 150 mg/day. Antidyskinetic: 25–50 mg every 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 every 4–6 hr (not to exceed 150 mg/day). Antidyskinetic: 1–1.5 mg/kg every 6–8 hr as needed (not to exceed 300 mg/day). Antitussive: 12.5 mg every 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 every 4–6 hr (not to exceed 37.5 mg/day). Antidyskinetic: 1–1.5 mg/kg every 4–6 hr as needed (not to exceed 300 mg/day). Antitussive: 6.25 mg every 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 every 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.

AllerMax, Banophen, Benadryl Dye-Free Allergy, Benadryl Allergy, Benadryl, Compoz, Compoz Nighttime Sleep Aid, Diphen AF, Diphen Cough, Genahist, 40 Winks, Hyrexin-50, Maximum Strength Nytol, Maximum Strength Sleepinal, Midol PM, Miles Nervine, 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

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

• 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.

Therapeutic Classification: allergy, cold and cough remedies, antihistamines, antitussives

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/Excretion: 95% metabolized by the liver.

Half-life: 2.4–7 hr.

Aller-Aide, Allerdryl, Allergy Formula, Allernix, Benylin, Calmex, Dimetane Allergy, Diphenhist, Dormex, Dormiphen, Insomnal, Nadryl

(antihistaminic effects)

• 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, including opioids, concurrently with this medication.
  • Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected and to avoid breastfeeding during therapy. Monitor infants exposed to diphenhydramine through breast milk for irritability and drowsiness.
  • Pedi: 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 breastfeeding or to children <4 yr.
  • Geri: 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.

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