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Pharmacology Made Easy 4.0 ?The Respiratory System
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Question: 25 ?of 25
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A nurse is preparing to administer phenylephrine to a client. The nurse should identify that that which of the following manifestations is an adverse effect of this drug?
Headache
Sleepiness
Hypotension
Constipation
The correct answer and explanation is:
Correct Answer: Headache
Explanation:
Phenylephrine is a selective alpha-1 adrenergic agonist commonly used as a decongestant, vasopressor, and mydriatic agent. It works by stimulating alpha-1 adrenergic receptors, causing vasoconstriction, which reduces nasal congestion and increases blood pressure in hypotensive states.
Adverse Effects of Phenylephrine:
One of the most commonly reported adverse effects of phenylephrine is a headache. This occurs because the vasoconstriction it induces can lead to increased vascular resistance, which may increase intracranial pressure and result in headaches.
Other Adverse Effects:
- Sleepiness: Phenylephrine is less likely to cause sedation or sleepiness compared to medications with central nervous system (CNS) effects, such as antihistamines. Its action is primarily peripheral, sparing CNS involvement.
- Hypotension: Instead of causing hypotension, phenylephrine is more commonly associated with hypertension due to its vasoconstrictive properties. It is used therapeutically to manage low blood pressure in certain conditions.
- Constipation: Constipation is not a direct or common adverse effect of phenylephrine. Drugs affecting the gastrointestinal system, such as anticholinergics or opioids, are more likely to cause this symptom.
Mechanism Behind the Adverse Effect:
Phenylephrine’s primary action on blood vessels can lead to changes in blood flow and pressure. In the nasal mucosa, vasoconstriction reduces swelling, but systemic absorption can cause widespread vasoconstriction. This increase in vascular tone may indirectly contribute to headaches as blood flow to certain areas is altered.
Nursing Considerations:
- Monitor for hypertension or signs of cerebrovascular strain (e.g., severe headache).
- Advise clients to report persistent or severe headaches.
- Use with caution in clients with cardiovascular or cerebrovascular disorders due to potential exacerbation.
In summary, while phenylephrine is effective for its therapeutic purposes, headache is a notable adverse effect requiring monitoring and patient education.