Diphenhydramine is an antihistamine used to relieve symptoms of allergy, hay fever, and the common cold. These symptoms include rash, itching, watery eyes, itchy eyes/nose/throat, cough, runny nose, and sneezing. It is also used to prevent and treat nausea, vomiting and dizziness caused by motion sickness.
Ethanolamine Derivative; Antihistamine
Diphenhydramine has anti-histaminic (H1-receptor), anti-emetic, anti-vertigo and sedative and hypnotic properties. The anti-histamine action occurs by blocking the spasmogenic and congestive effects of histamine by competing with histamine for H1 receptor sites on effector cells, preventing but not reversing responses mediated by histamine alone. Such receptor sites may be found in the gut, uterus, large blood vessels, bronchial muscles, and elsewhere. Anti-emetic action is by inhibition at the medullary chemoreceptor trigger zone. Anti-vertigo action is by a central antimuscarinic effect on the vestibular apparatus and the integrative vomiting center and medullary chemoreceptor trigger zone of the midbrain.
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. PARENTERAL Allergic conditions: Adult: As hydrochloride: 10-50mg 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.
Antidepressants, particularly of the tricyclic and monoamine oxidase inhibitor types may interact with diphenhydramine. MAO inhibitors prolong and intensify the anticholinergic effects of antihistamines. The CNS effect is increased by alcohol and other CNS depressant drugs.
Hypersensitivity; neonates, lactation. Epilepsy; elderly; performing tasks which require mental alertness; angleclosure glaucoma; pyroduodenal obstruction; urinary tract obstruction; hyperthyroidism; raised intraocular pressure; CV disease; acute asthma; pregnancy.
CNS depression, dizziness, headache, sedation; paradoxical stimulation in children; dryness of mouth, thickened resp secretion, blurring of vision, urinary retention; GI disturbances; blood dyscrasias.
Use is recommended only if clearly needed and the benefit outweighs the risk. Use is not recommended during breastfeeding.
Antihistamine over dosage reactions may vary from central nervous system depression to stimulation. Stimulation is particularly likely in children. Atropine-like signs and symptoms such as dryness of mouth, fixed and dilated pupils, flushing and gastrointestinal symptoms may also occur.
Do not store above 30°C temperature. Keep way from light and wet place. Keep out of reach of children.
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