KPSC Staff Nurse - 2018
Pharmacology
Easy
A patient who takes an antihistamine medication diphenhydramine, what would be the expected side effect of the drug?
Appeared in: KPSC Staff Nurse - 2018
Explanation
- Diphenhydramine is a first-generation H₁ antagonist, a class of drugs known for significant anticholinergic (drying) and sedative side effects.
- The anticholinergic action of diphenhydramine blocks acetylcholine receptors in salivary glands, leading to reduced saliva production and the sensation of a dry mouth (xerostomia).
- This effect is a direct and predictable consequence of the drug's mechanism of action and is one of the most commonly reported side effects.
- Other anticholinergic effects include urinary retention, constipation, and blurred vision.
Why Other Options Were Wrong
- Option A: Nervousness is a symptom of central nervous system (CNS) stimulation. Diphenhydramine is a CNS depressant, causing sedation and drowsiness, not stimulation.
- Option B: Palpitations (a rapid, strong, or irregular heartbeat) are not a typical side effect. While high doses or overdose can cause tachycardia, it's not an expected effect at therapeutic doses.
- Option D: Tremors are associated with CNS stimulation. Diphenhydramine's primary CNS effect is depression (sedation).
Related Visual
Clinical Relevance
- Nursing practice connection: Use the key finding related to Side effects of first-generation antihistamines to guide bedside assessment, documentation, and the next nursing action.
- Nurses should advise patients experiencing dry mouth to take sips of water, chew sugar-free gum, or use artificial saliva products to alleviate discomfort and prevent dental caries.
- A critical patient safety instruction is to warn patients about drowsiness and to avoid driving or operating heavy machinery until they know how the medication affects them.
- What if the patient was elderly? The risk of confusion, falls (due to sedation and dizziness), and urinary retention increases significantly, making first-generation antihistamines generally inappropriate for this population (Beers Criteria). A second-generation antihistamine would be a safer choice.
How to Approach the Question
- First, identify the drug mentioned: diphenhydramine.
- Recall or determine its drug class: It is a first-generation antihistamine.
- Remember the characteristic side effect profile for this class: strong anticholinergic effects (dry mouth, urinary retention, constipation, blurred vision) and sedation.
- Evaluate the given options against this profile.
- Recognize that 'Dry mouth' is a classic anticholinergic side effect.
- Eliminate the other options (Nervousness, Palpitation, Tremors) as they represent stimulant effects, which are opposite to the sedative nature of diphenhydramine.
Concept Tested & Keywords
- Concept Tested: Side effects of first-generation antihistamines
- Stem keywords: antihistamine, diphenhydramine, side effect
- Lead-in keywords: expected
- Negative lead-in flag: false
Question ID
QiWXRkJbcXQI_0dWRldFCQ
Reference Book
E6 Pharmacology Nursing Lilley 11e Part 2 p. 263-265
E6 Robert Boland, Marcia L. Verduin - Kaplan and Sadock's Comprehensive Text of Psychiatry-Wolters Kluwer Health (2024) (pp 1-16525 of 16525) pp. 10794-10796, 10863-10865
Practise the full KPSC Staff Nurse - 2018
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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