It is metabolized and excreted in the urine. Diphenhydramine is a competitive antagonist of the H1-histamine receptor, having antiallergic and antiemetic properties as well as being sedative. The anticholinergic actions of most antihistamines provide a drying effect on the nasal mucosa. Diphenhydramine is well absorbed from the gastrointestinal tract. The onset of action is 15 to 60 minutes, the half-life is 3 to 4 hours and the duration of action is 4 to 7 hours.
Decongestant products relieve nasal congestion.
Pre-existing respiratory depression. Patients receiving or having received MAO inhibitors in the preceding 3 weeks. There is enough drug in the package to seriously harm a child. This preparation should not be administered to children under 2 years of age, except on the advice of a physician. If the medicine causes drowsiness, reduce dosage and avoid activities requiring alertness.