Allerdryl , Benadryl, Benadryl Dye-Free, Sleep-Eze 3, Sominex Formula 2, Tusstat, Twilite, Valdrene
Classifications: antihistamine; h1-receptor antagonist; Therapeutic: antihistamine; h1-receptor antagonist; antivertigo; antiemetic; sedative-hypnotic; antiparkinson; antidyskinetic
Pregnancy Category: C
25 mg, 50 mg capsules, tablets; 6.25 mg/5 mL, 12.5 mg/5 mL syrup; 50 mg/mL injection
Diphenhydramine is an H1-receptor antagonist and antihistamine with significant anticholinergic activity. Competes for H1-receptor sites on effector cells, thus blocking histamine release. Effects in parkinsonism and drug-induced extrapyramidal
symptoms are apparently related to its ability to suppress central cholinergic activity and to prolong action of dopamine
by inhibiting its reuptake and storage.
Has antihistamine, antivertigo, antiemetic, antianaphylactic, antitussive, antidyskinetic, and sedative-hypnotic effects.
Temporary symptomatic relief of various allergic conditions and to treat or prevent motion sickness, vertigo, and reactions
to blood or plasma in susceptible patients. Also used in anaphylaxis as adjunct to epinephrine and other standard measures
after acute symptoms have been controlled; in treatment of parkinsonism and drug-induced extrapyramidal reactions; as a
nonnarcotic cough suppressant; as a sedative-hypnotic; and for treatment of intractable insomnia.
Hypersensitivity to antihistamines of similar structure; lower respiratory tract symptoms (including acute asthma); narrow-angle
glaucoma; prostatic hypertrophy, bladder neck obstruction; GI obstruction or stenosis; pregnancy (category C), lactation,
premature neonates, and neonates; use as nighttime sleep aid in children <2 y.
History of asthma; COPD; convulsive disorders; increased IOP; hyperthyroidism; hypertension, cardiovascular disease; hepatic
disease; diabetes mellitus; older adults, infants, and young children.
Route & Dosage
|Allergy Symptoms, Antiparkinsonism, Motion Sickness, Nighttime Sedation
Adult: PO 2550 mg t.i.d. or q.i.d. (max: 300 mg/d) IV/IM 1050 mg q46h (max: 400 mg/d)
Child: PO 26 y, 6.25 mg q46h (max: 300 mg/24 h); 612 y, 12.525 mg q46h (max: 300 mg/24 h) IV/IM 5 mg/kg/d divided into 4 doses (max: 300 mg/d)
Adult: PO 25 mg q46h (max: 100 mg/d)
Child: PO 26 y, 6.25 mg q46h (max: 25 mg/24 h); 612 y, 12.5 mg q46h (max: 50 mg/24 h)
- Give with food or milk to lessen GI adverse effects.
- For motion sickness: Give the first dose 30 min before exposure to motion; give remaining doses before meals and at bedtime.
- Give IM injection deep into large muscle mass; alternate injection sites. Avoid perivascular or SC injections because of
its irritating effects.
- Note: Hypersensitivity reactions (including anaphylactic shock) are more likely to occur with parenteral than PO administration.
PREPARE: Direct: Give undiluted.
ADMINISTER: Direct: Give at a rate of 25 mg or a fraction thereof over 1 min.
INCOMPATIBILITIES Solution/additive: Amphotericin B, dexamethasone, iodipamide, methylprednisolone, pentobarbital, phenobarbital, phenytoin, thiopental. Y-site: Allopurinol, amphotericin B cholesteryl complex, cefmetazole, foscarnet, furosemide.
- Store in tightly covered containers at 15°30° C (59°86° F) unless otherwise directed by manufacturer.
Keep injection and elixir formulations in light-resistant containers.
Adverse Effects (≥1%)CNS: Drowsiness,
dizziness, headache, fatigue
, disturbed coordination, tingling, heaviness and weakness of hands, tremors, euphoria, nervousness,
restlessness, insomnia; confusion; (especially in children): excitement, fever. CV:
mild hypotension or hypertension, cardiovascular collapse. Special Senses:
Tinnitus, vertigo, dry nose, throat, nasal stuffiness; blurred vision, diplopia, photosensitivity, dry eyes. GI: Dry mouth,
nausea, epigastric distress, anorexia, vomiting, constipation
, or diarrhea. Urogenital:
Urinary frequency or retention, dysuria. Body as a Whole:
Hypersensitivity (skin rash, urticaria, photosensitivity, anaphylactic shock
Thickened bronchial secretions, wheezing, sensation of chest tightness.
Diagnostic Test Interference
Diphenhydramine should be discontinued 4 d prior to skin testing procedures for allergy because it may obscure otherwise positive reactions.
and other cns depressants
, mao inhibitors
compound CNS depression
Readily absorbed from GI tract but only 4060% reaches systemic circulation. Onset:
1530 min. Peak:
14 h. Duration:
47 h. Distribution:
Crosses placenta; distributed into breast milk. Metabolism:
In liver; some degradation in lung and kidney. Elimination:
Mostly in urine within 24 h.
Assessment & Drug Effects
- Monitor cardiovascular status especially with preexisting cardiovascular disease.
- Monitor for adverse effects especially in children and the older adult.
- Supervise ambulation and use side-rails as necessary. Drowsiness is most prominent during the first few days of therapy
and often disappears with continued therapy. Older adults are especially likely to manifest dizziness, sedation, and hypotension.
Patient & Family Education
- Do not use alcohol and other CNS depressants because of the possible additive CNS depressant effects with concurrent use.
- Do not drive or engage in other potentially hazardous activities until the response to drug is known.
- Increase fluid intake, if not contraindicated; drug has an atropine-like drying effect (thickens bronchial secretions) that
may make expectoration difficult.