Diphenhydramine (Benadryl) Drug Study

Diphenhydramine (Benadryl) Overview

Diphenhydramine hydrochloride, known by the brand name Benadryl, is a widely used first-generation antihistamine. Its primary function is to alleviate allergy symptoms such as sneezing, itching, and runny nose. Additionally, it serves multiple other roles including treating motion sickness, and Parkinsonism, providing a nighttime sleep aid, and acting as an antitussive (cough suppressant).

This medication works by blocking acetylcholine and H-1 receptors, leading to its sedative, anticholinergic, and antiemetic effects.

Generic Name:

Diphenhydramine hydrochloride

Brand Name:

Benadryl

Classification:

Antihistamine, first-generation, ethanolamine

Uses

• Treatment of hypersensitivity reactions
• Treatment of motion sickness
• Treatment of Parkinsonism
• Nighttime sleep aid
• Antitussive
• Adjunctive therapy for anaphylactic reactions

Actions

• Exhibits sedative, anticholinergic, and antiemetic effects
• Blocks the action of acetylcholine
• Blocks H-1 receptors on effector cells of the GI tract, blood vessels, and respiratory tract

Contraindications

• Use with other products containing diphenhydramine
• Hypersensitivity to antihistamines
• Newborns and premature infants

Special Concerns:

• Elderly: Increases the risk of cognitive decline
• Use with caution in clients with:
  • Increased intraocular pressure
  • Closed-angle glaucoma
  • Chronic constipation
  • Hypertension
  • Stenosing peptic ulcer
  • Bladder obstruction
  • Enlarged prostate
  • Overactive thyroid
  • Asthma

Side Effects

• Drowsiness
• Constipation
• Diarrhea
• Dizziness
• Dry mouth/nose/throat
• Headache
• Anorexia
• Nausea & Vomiting
• Anxiety
• Gastrointestinal upset
• Weakness (Asthenia)
• Blurred vision
• Fatigue

Dosage:

• Oral: 25-50 mg TID-QID
• IV: 10-50 mg, up to 100 mg/IV

Nursing Considerations

• Administer full prophylactic dose 30 minutes prior to travel if used as prophylaxis for motion sickness
• Take similar doses with meals and at bedtime
• Do not use for more than 2 weeks to treat insomnia
• For IV, may give undiluted
• Do not exceed the IV rate of 25 mg/minute
• The drug causes drowsiness; avoid activities requiring mental alertness
• Use sun protection as it may cause photosensitivity
• Use sugarless candy/gum to diminish dry mouth effects
• Avoid alcohol and other CNS depressants
• Discontinue therapy 72-96 hours before skin testing. Report adverse effects and lack of response
• Monitor for signs of anticholinergic effects such as dry mouth, urinary retention, and increased intraocular pressure
• Educate patients on potential interactions with other medications, including MAO inhibitors

References

1. World Health Organization. (2020). WHO model list of essential medicines. Retrieved from https://www.who.int/publications/i/item/WHO-MHP-20.10
2. Centers for Disease Control and Prevention. (2020). Diphenhydramine information. Retrieved from https://www.cdc.gov/ncbddd/medications/diphenhydramine.html
3. MedlinePlus. (2020). Diphenhydramine. Retrieved from https://medlineplus.gov/druginfo/meds/a682539.html
4. Mayo Clinic. (2020). Diphenhydramine (oral route). Retrieved from https://www.mayoclinic.org/drugs-supplements/diphenhydramine-oral-route/proper-use/drg-20068588
5. Drugs.com. (2020). Diphenhydramine. Retrieved from https://www.drugs.com/diphenhydramine.html