Adult: 25-50 mg 3 or 4 times daily. Max: 300 mg daily. For prevention of motion sickness, administer 30 minutes before exposure to motion. Child: 2-6 years 6.25 mg 4-6 hourly; 6-12 years 12.5-25 mg 4-6 hourly; >12 years Same as adult dose. For prevention of motion sickness, administer 30 minutes before exposure to motion.
Oral Short-term management of insomnia
Adult: 50 mg given 30 minutes before bedtime as needed.
Parenteral Allergic conditions, Motion sickness
Adult: 10-50 mg up to 100 mg if needed via IV inj at a rate of 25 mg/min or deep IM inj. Max: 400 mg daily. For prevention of motion sickness, administer 30 minutes before exposure to motion. Child: 5 mg/kg via IV inj at a rate of 25 mg/min or deep IM inj in 4 divided doses. Max: 300 mg daily. For prevention of motion sickness, administer 30 minutes before exposure to motion.
Parenteral Parkinson's disease
Adult: 10-50 mg up to 100 mg if needed, via IV inj at a rate not exceeding 25 mg/min or via deep IM inj, when oral therapy is impossible or contraindicated. Max: 400 mg daily.
Topical/Cutaneous Pruritic skin disorders
Adult: As 2% cream: Apply to affected area(s) up to max bid for not more than 3 days. Child: ≥2 years Same as adult dose.
Administration
May be taken with or without food.
Incompatibility
IV/IM: Incompatible with amphotericin B, cefmetazole, cefalotin, hydrocortisone Na succinate, soluble barbiturates, contrast media, and strong acids or alkali solutions.
Contraindications
Stenosing peptic ulcer or pyloroduodenal obstruction. Premature infants and neonates. Lactation. Concomitant use with other antihistamine-containing medicines (including topical antihistamines).
Special Precautions
Patient with narrow-angle glaucoma, prostatic hypertrophy or genitourinary obstruction, urinary retention, asthma, bronchitis, COPD, CV disease (e.g. hypertension, ischaemic heart disease), thyroid disorder, myasthenia gravis, seizure disorders (e.g. epilepsy). Moderate to severe renal and hepatic impairment. Elderly. Pregnancy.
Adverse Reactions
Significant: Drug tolerance (continuous use). Rarely, eczematous reactions (topical). Blood and lymphatic system disorders: Haemolytic anaemia, thrombocytopenia, agranulocytosis. Cardiac disorders: Palpitations, tachycardia, extrasystoles. Gastrointestinal disorders: Dry mouth, epigastric distress, nausea, vomiting, diarrhoea, constipation. General disorders and admin site conditions: Fatigue. Metabolism and nutrition disorders: Anorexia. Nervous system disorders: Sedation, drowsiness, restlessness, dizziness, excitability (children), headache. Psychiatric disorders: Disturbance in attention, confusion, nervousness. Renal and urinary disorders: Urinary frequency, urinary retention, difficulty in micturition. Respiratory, thoracic and mediastinal disorders: Thickening of bronchial secretions. Skin and subcutaneous tissue disorders: Sensitisation reaction, photosensitivity. Vascular disorders: Hypotension.
This drug may cause drowsiness or sedation, dizziness, blurred vision, cognitive and psychomotor impairment, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor mental alertness.
Overdosage
Symptoms: Drowsiness, sedation, mydriasis, fever, flushing, agitation, tremor, dystonic reactions, hallucination, ECG changes. Severe cases: Rhabdomyolysis, convulsions, delirium, toxic psychosis, arrhythmias, coma, cardiovascular collapse. May result in hallucinations, convulsions and death in paediatrics patients. Management: Supportive and symptomatic treatment. Administer parenteral diazepam for treatment of convulsions and marked CNS stimulation. May give vasopressors to treat hypotension.
Drug Interactions
May increase sedative effects of other CNS depressants (e.g. tranquilizers, hypnotics, anxiolytics). Enhanced and prolonged anticholinergic effects with MAOIs. May potentiate effects of anticholinergic agents (e.g. atropine, TCA). May diminish therapeutic effect of betahistine. Potentially Fatal: Enhanced CNS depressant effects with other antihistamines (e.g. hydroxyzine).
Food Interaction
May potentiate sedative effects of alcohol.
Lab Interference
May give false-positive result in urine detection of methadone and phencyclidine, serum TCA screening. May suppress wheal and flare reactions to skin test antigens.
Action
Description: Mechanism of Action: Diphenhydramine, a monoethanolamine derivative, is an antihistamine with sedative and antimuscarinic properties. It competes with histamine for H1 receptor sites on effector cells in the blood vessels, gastrointestinal tract, and respiratory tract. Duration: Histamine-induced wheal suppression: ≤10 hours; histamine-induced flare suppression: ≤12 hours. Pharmacokinetics: Absorption: Well absorbed from the gastrointestinal tract. Bioavailability: 42-62%. Time to peak plasma concentration: Approx: 1-4 hours. Distribution: Widely distributed throughout the body including the CNS. Crosses the placenta, enters breastmilk. Volume of distribution: 17 L/kg. Plasma protein binding: 98.5%. Metabolism: Extensively metabolised in the liver by CYP2D6 isoenzyme via N-demethylation and minor demethylation by CYP1A2, 2C9, 2C19; smaller degrees in pulmonary and renal systems; undergoes significant first-pass effect. Excretion: Mainly via urine (as metabolites and unchanged drug). Elimination half-life: 2.4-9.3 hours.
Chemical Structure
Source: National Center for Biotechnology Information. PubChem Database. Diphenhydramine, CID=3100, https://pubchem.ncbi.nlm.nih.gov/compound/Diphenhydramine (accessed on Jan. 21, 2020)
Storage
Store below 25°C. Protect from light and moisture.
R06AA02 - diphenhydramine ; Belongs to the class of aminoalkyl ethers used as systemic antihistamines. D04AA32 - diphenhydramine ; Belongs to the class of topical antihistamines used in the treatment of pruritus.
References
Anon. Diphenhydramine (Systemic). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 05/09/2019.Anon. Diphenhydramine (Topical). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 05/09/2019.Buckingham R (ed). Diphenhydramine. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 05/09/2019.Diphenhydramine Liquid (Major Pharmaceuticals). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 05/09/2019.Diphenhydramine Solution for Injection (Fresenius Kabi USA, LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 05/09/2019.Diphenhydramine Tablet (Rugby Laboratories). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 05/09/2019.Histergan Cream (Norma Chemicals Ltd.). MHRA. https://products.mhra.gov.uk/. Accessed 05/09/2019.Histergan/Paxidorm Tablets (Norma Chemicals Ltd.). MHRA. https://products.mhra.gov.uk/. Accessed 09/09/2019.
Sign Out
