Which of the following is a sign of magnesium toxicity?

• A. Absent deep tendon reflexes
• B. Stable heart rhythm
• C. Increased urine output
• D. Sharp headache

Answer: (A)

The presence of absent deep tendon reflexes is a known sign of magnesium toxicity. Magnesium plays a critical role in neuromuscular function, and elevated levels can disrupt normal neurological responses. When magnesium becomes toxic in the body, it acts as a central nervous system depressant, which can lead to a reduction or absence of reflexes as the signals between nerves and muscles become impaired. This is a serious condition that can indicate that magnesium levels have reached a point where they could cause harm to the patient, necessitating immediate medical attention to prevent further complications.

In contrast, other options like having a stable heart rhythm, increased urine output, or a sharp headache do not effectively indicate magnesium toxicity. A stable heart rhythm typically suggests that magnesium levels are within a normal range since magnesium is crucial for cardiovascular health. Additionally, increased urine output may suggest that the kidneys are functioning properly and are able to excrete excess magnesium, indicating that there is not a toxicity issue. A sharp headache is a vague symptom that could be related to various conditions and is not specific to magnesium levels in the body. Therefore, absent deep tendon reflexes is the most appropriate indicator of magnesium toxicity.