Indications |
Oral Allergic conditions Adult: As hydrochloride: 25-50 mg 3-4 times daily. Max: 300 mg/day. Child: 6.25-25 mg 3-4 times daily, up to 5 mg/kg in divided doses. Max: 300 mg/day. Oral Treatment and prophylaxis of motion sickness Adult: As diphenhydramine di (acefyllinate): Usual dose: 90-135 mg, may repeat if needed at intervals of at least 6 hr. Max: 540 mg daily. For prevention, dose to be given at least 30 min before travelling. Parenteral Allergic conditions Adult: As hydrochloride: 10-50 mg as a 1% or 5% solution, up to 100 mg. Dose may be given via deep IM or IV inj. Not more than 400 mg in 24 hr. Child: 5 mg/kg daily in 4 divided doses. Dose can be given via deep IM or IV inj. Max: 300 mg in 24 hr. |
Contraindications |
Hypersensitivity ; neonates, lactation. |
Warnings / Precautions |
Epilepsy; elderly; performing tasks which require mental alertness; angle-closure glaucoma; pyroduodenal obstruction; urinary tract obstruction; hyperthyroidism; raised intraocular pressure; CV disease; acute asthma; pregnancy. |
Adverse Reactions |
CNS depression, dizziness, headache, sedation; paradoxical stimulation in children; dryness of mouth, thickened respiratory secretion, blurring of vision, urinary retention; GI disturbances; blood dyscrasias. |
Overdose Reactions |
Symptoms: Acute delirium with visual and auditory hallucinations, impaired consciousness, psychosis, seizures, antimuscarinic symptoms (e.g. mydriasis, tachycardia and tachyarrhythmias), rhabdomyolysis and respiratory failure. |
Drug Interactions |
Masks ototoxicity produced by aminoglycosides. Increases gastric degradation of levodopa and decreases its absorption by reduction of gastric emptying. Antagonises therapeutic effects of cholinergic agents e.g. tacrine, donezepil and neuroleptics. Valerian, St. John's wort, Kava Kava and gotu kola may increase CNS depression. Potentially Fatal: Potentiates CNS depression with alcohol, barbiturates, analgesics, sedatives and neuroleptics. Additive antimuscarinic action with MAOIs, atropine and TCAs. See Below for More diphenhydramine Drug Interactions |
Mechanism of Actions |
Diphenhydramine blocks histamine H1-receptors on effector cells of the GI tract, blood vessels and respiratory tract. It also causes sedation and has some anticholinergic action. Absorption: Absorbed well from the GI tract (oral); peak plasma concentrations after 1-4 hr. Distribution: Widely distributed, CNS; crosses the placenta and enters breast milk. Protein-binding:Highly bound. Metabolism: Extensive first-pass metabolism. Excretion: Via urine (as metabolites, small amounts as unchanged drug); 1-4 hr (elimination half-life). |
Administration |
May be taken with or without food. |
Storage Conditions |
Oral: Store at 15-25°C. Parenteral: Store at 15-25°C. |
ATC Classification |
D04AA32 - diphenhydramine ; Belongs to the class of topical antihistamines used in the treatment of pruritus. R06AA02 - diphenhydramine ; Belongs to the class of aminoalkyl ethers used as systemic antihistamines. |
Storage |
Oral: Store at 15-25°C. Parenteral: Store at 15-25°C. |
Available As |
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Diphenhydramine
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Diphenhydramine Containing Brands
Diphenhydramine is used in following diseases
Drug - Drug Interactions of Diphenhydramine
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