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diphenhydramine (oral, parenteral), (dye-fen-hye-dra-meen)

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Therapeutic: allergy, cold, and cough remedies, antihistamines, antitussives


Relief of allergic symptoms caused by histamine release, including Anaphylaxis, Seasonal and perennial allergic rhinitis, Allergic dermatoses. Parkinson's disease, and dystonic reactions from medications. Mild nighttime sedation. Prevention of motion sickness. Antitussive (syrup only).


Antagonizes the effects of histamine at H1-receptor sites; does not bind to or inactivate histamine. Significant CNS depressant and anticholinergic properties. Therapeutic Effects: Decreased symptoms of histamine excess (sneezing, rhinorrhea, nasal and ocular pruritus, ocular tearing and redness, urticaria). Relief of acute dystonic reactions. Prevention of motion sickness. Suppression of cough.

Adverse Reactions/Side Effects

CNS: drowsiness, dizziness, headache, paradoxical excitation (increased in children). EENT: blurred vision, tinnitus. CV: hypotension, palpitations. GI: anorexia, dry mouth, constipation, nausea. GU: dysuria, frequency, urinary retention. Derm: photosensitivity. Resp: chest tightness, thickened bronchial secretions, wheezing. Local: pain at IM site.


Examination and Evaluation

  • Assess blood pressure periodically and compare to normal values (See Appendix F). Report a sustained or symptomatic decrease in blood pressure (hypotension) or other cardiac symptoms (palpitations).

  • Monitor respiratory function at rest and during exercise. Notify physician if patient experiences any troublesome wheezing, tightness in the throat or chest, or abnormal bronchial secretions.

  • Monitor symptoms of seasonal allergies (sneezing, rhinitis, itching eyes, cough) or allergic skin reactions (rash, hives, itching) to help document benefits of this drug in treating these disorders.

  • If used as a cough suppressant, assess frequency and nature of cough, lung sounds, and amount and type of sputum produced. Document whether this drug is effective as a cough suppressant.

  • If used to treat Parkinson's disease, assess patient's motor function, especially when starting drug therapy, or during dosing changes or addition of other antiparkinson drugs. Motor function should be assessed at different times of the day, such as when drugs are reaching peak therapeutic levels (i.e., 2–4 hr after oral dose), as well as when drug effects are minimal (just before the next dose).

  • When treating anaphylaxis, assess for signs of successful treatment, including decreased skin reactions (rash, urticaria) and increased airway patency and ventilation (decreased dyspnea, wheezing, shortness of breath).

  • Assess dizziness and drowsiness that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician, and caution the patient and family/caregivers to guard ...

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