Generic Name

Diphenhydramine Hydrochloride

Precaution

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. Lactation: Drug enters breast milk; contraindicated

Indication

Allergic rhinitis, Allergic conditions, Motion sickness, Common cold, Insomnia, Extrapyramidal symptoms

Contra Indication

Hypersensitivity ; neonates, lactation.

Dose

N/A

Side Effect

Chest tightness, extrasystoles, hypotension, palpitations, tachycardia; ataxia, chills, confusion, dizziness, drowsiness, euphoria, excitement, fatigue, headache, insomnia, irritability, nervousness, neuritis, paraesthesia, paradoxical excitation, restlessness, sedation, seizure, vertigo; diaphoresis; menstrual disease; GI disturbances (e.g. anorexia, constipation, diarrhoea); difficulty in micturition, urinary frequency, urinary retention; agranulocytosis, haemolytic anaemia, thrombocytopenia; anaphylactic shock; tremor; blurred vision, diplopia; acute labyrinthitis, tinnitus; constriction of pharynx, nasal congestion, thickening of bronchial secretions, wheezing;

Pregnancy Category

Mode of Action

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.

Interaction

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.

Pregnancy Category Note

Pregnancy category: B Lactation: Drug enters breast milk; contraindicated

Adult Dose

Oral Allergic conditions; Treatment and prophylaxis of motion sickness Adult: 25-50 mg 3-4 times daily. For prevention of motion sickness, admin 30 min before exposure to motion. Max: 300 mg daily. Parkinson's disease Adult: Initially, 25 mg tid, may increase to 50 mg 4 times daily if necessary. Short-term management of insomnia Adult: 50 mg 30 min before bedtime as needed. Hepatic impairment: No dosage adjustment needed.

Child Dose

Allergic Reaction 2-6 years: 6.25 mg q4-6hr; not to exceed 37.5 mg/day 6-12 years: 12.5-25 mg PO q4-6hr; not to exceed 150 mg/day >12 years: 25-50 mg PO q4-6hr; not to exceed 300 mg/day Occasional Insomnia >12 years: 50 mg PO 30 minutes before bedtime Cough <12 years: Safety and efficacy not established >12 years: 25-50 mg PO q4-6hr; not to exceed 300 mg/day Motion Sickness Administer 30 min before motion 12.5-25 mg PO q6-8hr or 150 mg/m² ; not to exceed 300 mg/day

Renal Dose

Renal impairment: No dosage adjustment needed.

Administration

May be taken with or without food.