Which of the following clinical feature is an earliest feature of magnesium toxicity?

NORCET-7 Mains-2024

Pharmacology

Easy

Appeared in: NORCET-7 Mains-2024

Explanation

Magnesium toxicity first manifests as neuromuscular blockade due to its action as a central nervous system depressant.
The loss of deep tendon reflexes (DTRs), particularly the patellar reflex, is the earliest and most common clinical sign of developing toxicity.
This sign typically appears when serum magnesium levels rise to 7–10 mEq/L, which is above the therapeutic range.
Recognizing the loss of DTRs is critical as it serves as a warning sign before more severe, life-threatening complications like respiratory depression and cardiac arrest occur.

Option A: Magnesium toxicity does not cause increased urine output. Instead, decreased urine output (oliguria) is a primary risk factor for toxicity because the kidneys are responsible for excreting magnesium.
Option B: Magnesium is a central nervous system depressant. Therefore, toxicity leads to respiratory depression (a decreased respiratory rate), not an increased rate.
Option D: Magnesium causes peripheral vasodilation and smooth muscle relaxation, which results in hypotension (decreased blood pressure).

Visual 1: Table: Progression of Magnesium Toxicity. A table showing serum magnesium levels (in mEq/L and mg/dL) and the corresponding clinical signs, from therapeutic range to loss of reflexes, respiratory depression, and cardiac arrest.

Clinical Relevance

Nursing practice connection: Knowing Early clinical signs of magnesium toxicity helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses administering intravenous magnesium sulfate must perform and document hourly assessments, including deep tendon reflexes, respiratory rate, level of consciousness, and urine output, to detect toxicity at its earliest stage.
The antidote for magnesium toxicity, calcium gluconate, must always be kept in a readily accessible location (e.g., at the bedside) whenever a patient is receiving a magnesium sulfate infusion.
What if? If a patient receiving magnesium sulfate has absent patellar reflexes but is otherwise stable, the nurse's first action is to stop the infusion immediately and notify the healthcare provider. This prevents progression to more severe toxicity.

How to Approach the Question

First, identify the key term in the question: "earliest feature" of "magnesium toxicity."
Recall the primary action of magnesium sulfate: it is a central nervous system (CNS) and neuromuscular depressant.
Consider the dose-dependent effects of a CNS depressant. The effects will progress from mild depression to severe depression of bodily functions.
Evaluate the options in the context of progressive depression:
Neuromuscular function (reflexes) is sensitive and will be affected first.
Respiratory function is a more vital function and will be depressed at higher, more toxic levels.

Concept Tested & Keywords

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