Brand Name
Allerdryl (CAN), Banophen, Benadryl, Benadryl Allergy, Diphenhist
CapTabs, Genahist, Hyrexin, Nytol QuickCaps, Siladryl, Sleep-Eze D Extra
Strength, Unisom SleepGels Maximum Strength
Class and Category
Chemical class: Ethanolamine derivative
Therapeutic class: Antianaphylactic adjunct, antidyskinetic,
antiemetic, antihistamine, antitussive (syrup), antivertigo, sedativehypnotic
Pregnancy category: B
Indications and Dosages
To treat hypersensitivity reactions, such as perennial and
seasonal allergic rhinitis, vasomotor rhinitis, allergic conjunctivitis, uncomplicated
allergic skin eruptions, and transfusion reactions
CAPSULES, TABLETS
Adults and adolescents. 25 to 50 mg every 4 to 6 hr,
p.r.n. Maximum: 300 mg daily.
Children ages 6 to 12. 12.5 to 25 mg every 4 to 6 hr. Maximum:
150 mg daily.
Children up to age 6. 6.25 to 12.5 mg every 4 to 6 hr.
ELIXIR
Adults and adolescents. 25 to 50 mg every 4 to 6 hr,
p.r.n. Maximum: 300 mg daily.
Children. 1.25 mg/kg every 4 to 6 hr. Maximum: 300
mg daily.
I.V. OR I.M. INJECTION
Adults and adolescents. 10 to 50 mg every 4 to 6 hr up to
100 mg/dose, if needed. Maximum: 400 mg daily.
Children. 1.25 mg/kg every 4 to 6 hr. Maximum: 300
mg daily.
To treat sleep disorders
CAPSULES, TABLETS
Adults and adolescents. 50 mg 20 to 30 min before
bedtime.
To provide antitussive effects
ELIXIR
Adults and adolescents. 25 mg every 4 hr. Maximum: 100
mg/24 hr.
Children ages 6 to 12. 12.5 mg every 4 to 6 hr. Maximum:
75 mg daily.
Children ages 2 to 6. 6.25 mg every 4 to 6 hr. Maximum:
25 mg daily.
To prevent motion sickness or treat vertigo
CAPSULES, ELIXIR, TABLETS
Adults and adolescents. 25 to 50 mg every 4 to 6 hr,
p.r.n. Maximum: 300 mg daily.
Children. 1 to 1.5 mg/kg every 4 to 6 hr, p.r.n. Maximum:
300 mg daily.
I.V. OR I.M. INJECTION
Adults and adolescents. Initial: 10 mg. Increased
to 20 to 50 mg every 2 to 3 hr, if needed. Maximum: 100 mg/dose, 400 mg daily.
Children. 1 to 1.5 mg/kg I.M. every 4 to 6 hr, p.r.n. Maximum:
300 mg daily.
To treat symptoms of Parkinson’s disease and drug-induced
extrapyramidal reactions in elderly patients who can’t tolerate more potent
antidyskinetic drugs
CAPSULES, ELIXIR, TABLETS
Adults. 25 mg t.i.d. increased gradually to 50 mg q.i.d., if needed. Maximum:
300 mg daily.
I.V. OR I.M. INJECTION
Adults and adolescents. 10 to 50 mg q.i.d., as needed. Maximum:
100 mg/dose, 400 mg daily.
Route Onset Peak Duration
P.O. 15–60 min 1–3 hr 6–8 hr
I.V. Immediate 1–3 hr 6–8 hr
I.M. 30 min 1–3 hr 6–8 hr
Mechanism of Action
Binds to central and peripheral H1 receptors, competing with
histamine for these sites and preventing it from reaching its site of action.
By blocking histamine, diphenhydramine produces antihistamine effects, inhibiting
respiratory, vascular, and GI smooth-muscle contraction; decreasing capillary
permeability, which reduces wheals, flares, and itching; and decreasing salivary
and lacrimal gland secretions. Diphenhydramine produces antidyskinetic effects,
possibly by inhibiting acetylcholine in the CNS. It also produces antitussive effects
by directly suppressing the cough center in the medulla oblongata in the brain.
Diphenhydramine’s antiemetic and antivertigo effects may be related to its ability
to bind to CNS muscarinic receptors and depress vestibular stimulation and labyrinthine
function. Its sedative effects are related to its CNS depressant action.
Contraindications
Bladder
neck obstruction, hypersensitivity to diphenhydramine or its components, lower
respiratory tract symptoms (including asthma), MAO inhibitor therapy, narrow- angle
glaucoma, pyloroduodenal obstruction, stenosing peptic ulcer, symptomatic benign
prostatic hyperplasia
Interactions
DRUGS
apomorphine:
Possibly
decreased emetic response in treatment of poisoning
barbiturates,
other CNS depressants: Possibly\ increased CNS depression
MAO
inhibitors: Increased
anticholinergic and CNS depressant effects of diphenhydramine
ACTIVITIES
alcohol
use: Possibly
increased CNS depression
Adverse
Reactions
CNS:
Confusion,
dizziness, drowsiness
CV:
Arrhythmias,
palpitations, tachycardia
EENT:
Blurred
vision, diplopia
GI:
Epigastric
distress, nausea
HEME:
Agranulocytosis,
hemolytic anemia, thrombocytopenia
RESP:
Thickened
bronchial secretions
SKIN:
Photosensitivity
Nursing
Considerations
•
Expect to give parenteral form of diphenhydramine only when oral ingestion
isn’t possible.
•
Keep elixir container tightly closed. Protect elixir and parenteral forms from light.
•
Expect to discontinue drug at least 72 hours before skin tests for allergies
because drug may inhibit cutaneous histamine response, thus producing
false-negative results.
PATIENT
TEACHING
•
Instruct patient to take diphenhydramine at least 30 minutes before exposure to
situations that may cause motion sickness.
•
Advise her to take drug with food to minimize GI distress.
•
Urge patient to avoid alcohol while taking diphenhydramine.
•
Instruct her to use sunscreen to prevent photosensitivity reactions.
•
Advise patient to avoid taking other OTC drugs that contain diphenhydramine to prevent
additive effects.
