Adult Dosing

Allergic reactions, hypersensitivity reactions

• 10-50 mg IM/IV q4-6 hrs PRN. [Max: 100 mg/dose; 400 mg/day]

Extrapyramidal symptoms

• 10-50 mg IM/IV q4-6 hrs PRN. [Max: 100 mg/dose; 400 mg/day]

Motion sickness prevention

• Start 10-50 mg IM/IV 30 mins before exposure; may repeat q4-6 hrs PRN. [Max: 300 mg/day]

Pediatric Dosing

Anaphylaxis adjunct in addition to epinephrine

• Child other than premature infants and neonates
• 5 mg/kg/24 hr or 150 mg/m2/24 hr. Maximum daily dosage is 300 mg. Divide into four doses, administered intravenously at a rate generally not exceeding 25 mg/min, or deep intramuscularly.

Allergic reactions, hypersensitivity reactions

• Child (2-11 yrs): 1-2 mg/kg/dose IV/IM q6 hrs [Max 50 mg/dose; 300 mg/day]
• Child (>12 yrs): 25-50 mg IM/IV q2-4 hrs PRN. [Max: 100 mg/dose; 400 mg/day]

Extrapyramidal symptoms

• Child (2-11 yrs): 1-2 mg/kg/dose IV/IM q6-8 hrs [Max 50 mg/dose; 300 mg/day]
• Child (>12 yrs): 25-50 mg IM/IV q6-8 hrs PRN. [Max: 100 mg/dose; 400 mg/day]

Motion sickness prevention

• Child (2-5 yrs): Start 6.25 mg IM/IV 30 mins before exposure; may repeat q4-6 hrs PRN. [Max: 37.5 mg/day]
• Child (6-11 yrs): Start 12.5-25 mg IM/IV 30 mins before exposure; may repeat q4-6 hrs PRN. [Max: 150 mg/day]
• Child (>12 yrs): Start 25-50 mg IM/IV 30 mins before exposure; may repeat q4-6 hrs PRN. [Max: 300 mg/day]

• Diphenhydramine (IV) is indicated for the following conditions in adults and pediatric patients (other than premature infants and neonates)
• Relief of allergic symptoms caused by histamine release; amelioration of allergic reactions to blood or plasma; as an adjunct to epinephrine for management of anaphylactic reactions after the acute manifestations have been controlled
• Treatment of motion sickness
• Management of parkinsonism (including drug-induced) in elderly

• Hypersensitivity to any of the components of the product
• Newborn/premature infants
• Acute asthma
• MAO inhibitor therapy
• Lactation

• N/A

Renal Dose Adjustment

• Renal impairment: No dose adjustments
• Hemodialysis: No supplement

Hepatic Dose Adjustment

• Hepatic impairment: Dose adjustments not defined

• IV form is the acceptable only if oral route is impossible/contraindicated
• Diphenhydramine should be used with extreme caution in narrow angle glaucoma, prostatic hypertrophy, stenosing peptic ulcer disease and bladder obstruction
• It may cause drowsiness and/or sedation, which may be enhanced with alcohol, sedatives, and other CNS depressants. Do not engage in activities requiring mental alertness and motor coordination, such as driving a car or operating machinery
• Overdosage in children may cause hallucinations, convulsions, and death. Antihistamines may diminish mental alertness. In young children, use of this antihistamines may produce paradoxical excitation
• FDA does not recommend use in patients < 2 yrs (due to increased risk of deaths attributed to toxicity)

Cautions: Use cautiously in

• Renal impairment
• Hepatic impairment
• Hx. of bronchial asthma
• COPD
• Increased IOP
• Angle closure glaucoma
• CV disease
• Hypertension
• Pyloroduodenal obstruction
• PUD
• Prostatic hypertrophy
• Bladder neck obstruction
• Hyperthyroidism
• Pediatric population
• Geriatric population

Pregnancy Category:B

Breastfeeding: Small occasional doses of diphenhydramine would not be expected to cause any adverse effects in breastfed infants. Larger doses or more prolonged use may cause effects in the infant or decrease the milk supply, particularly when used in combination with a sympathomimetic agent or when lactation is not well established. The nonsedating antihistamines should be preferred. This information is based upon LactMed database (available at http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT last accessed 19 August 2009).

• CV: Hypotension, palpitations, tachycardia, extrasystoles
• CNS: Drowsiness, dizziness, headache, paradoxical excitation, excitation, insomnia, euphoria, vertigo
• NEURO: Paresthesia, tremor, convulsions, neuritis, disturbed coordination
• PSYCHIATRY: Confusion, irritability, nervousness
• EENT: Blurred vision, diplopia, dryness of nose and throat, tinnitus, acute labyrinthitis
• HEMA: Hemolytic anemia, thrombocytopenia, agranulocytosis
• DERM: Urticaria, drug rash, photosensitivity
• GI: Epigastric distress, anorexia, dryness of mouth, nausea, vomiting, diarrhea, constipation
• GU: Urinary frequency, urinary retention
• RESP: Thickening of bronchial secretions, wheezing, nasal stuffiness, chest tightness
• LOCAL: Pain at IM site
• MISC: Anaphylactic shock, excessive perspiration, chills, fatigue, restlessness

• Antihistamine; antagonizes effects of histamine at H1-receptor sites (non selective antihistamine); has anticholinergic properties produces significant CNS depression
• Extensively metabolized by liver via CYP450 enzymes (2D6 and 3A4)
• Renally excreted
• Half-life: 4 hrs

US Trade Name(s)

• Only generic available

US Availability

diphenhydramine (generic)

• INJ: 50 mg/mL (1 mL vials)

Canadian Trade Name(s)

• Diphenist

Canadian Availability

diphenhydramine (generic)

• INJ: 50 mg/mL

Diphenist

• INJ: 50 mg/mL

UK Trade Name(s)

• N/A

UK Availability

• N/A

Australian Trade Name(s)

• N/A

Australian Availability

• N/A

Allergy & Immunology

Antihistamines

Gastrointestinal

Antiemetics

Anticholinergic Antiemetics

Neurologic

Antiparkinson Agents

Anticholinergic Agents