DIPHENHYDRAMINE

Therapeutic Class: Drug to treat allergies

Pharmacologic Class: H₁-receptor antagonist; antihistamine

ACTIONS AND USES: Diphenhydramine is a first-generation H1-receptor antagonist whose primary use is to treat minor symptoms of allergy and the common cold such as sneezing, runny nose, and tearing of the eyes. Diphenhydramine is often combined with an analgesic, decongestant, or expectorant in OTC cold and flu products. Diphenhydramine is also administered topically to treat rashes, and intramuscular/intravenous (IM/IV) forms are available for severe allergic reactions. Other indications for diphenhydramine include Parkinson’s disease, motion sickness, and insomnia.

ADMINISTRATION ALERTS: There is an increased risk of anaphylactic shock when this drug is administered parenterally. When administering IV, inject at a rate of 25 mg/min to reduce the risk of shock. When administering IM, inject deep into a large muscle to minimize tissue irritation.

Pregnancy category: C

ADVERSE EFFECTS: First-generation H1-receptor antagonists such as diphenhydramine cause significant drowsiness, although this usually diminishes with long-term use. Occasionally, paradoxical CNS stimulation and excitability will be observed, rather than drowsiness. Excitation is more frequent in children than adults. Anticholinergic effects such as dry mouth, tachycardia, and mild hypotension occur in some patients. Diphenhydramine may cause photosensitivity.

Contraindications: Hypersensitivity to the drug, prostatic hypertrophy, narrow-angle glaucoma, and gastrointestinal (GI) obstruction are contraindications of use. The drug should be used cautiously in patients with asthma or hyperthyroidism.

INTERACTIONS: Drug–Drug: Use with CNS depressants such as alcohol or opioids will cause increased sedation. Other OTC cold preparations may increase anticholinergic side effects. Monoamine oxidase (MAO) inhibitors may cause a hypertensive crisis.

Lab Tests: Drug should be discontinued at least 4 days prior to skin allergy tests; otherwise, false-negative tests may result. Treatment of Overdose: Overdose may cause either CNS depression or excitation. There is no specific treatment for overdose

RELATED;

1. SHOCK  

2. ASTHMA  

3.  DRUG USE IN RELATION TO PREGNANCY  

4.  TOXICITY OF DRUGS AND ANTIDOTES

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