From the Guidelines
Magnesium administration is known to cause a reduction in deep tendon reflexes, which is a critical indicator of potential magnesium toxicity. This effect is dose-dependent, with higher serum magnesium levels leading to progressively diminished reflexes [ 1 ]. The mechanism behind this phenomenon involves magnesium's ability to block calcium release at the neuromuscular junction, thereby reducing muscle excitability and reflex responses.
Key Points to Consider
- At therapeutic magnesium levels (2-4 mEq/L), reflexes remain present but may be somewhat diminished
- When levels reach 4-7 mEq/L, DTRs become notably decreased
- At levels exceeding 10 mEq/L, reflexes typically disappear completely, signaling potential magnesium toxicity [ 1 ]
Clinical Implications
- Clinicians should routinely assess DTRs (particularly patellar and biceps reflexes) in patients receiving magnesium sulfate
- Regular monitoring of DTRs, along with respiratory rate and urine output, is essential for safe magnesium administration
- If reflexes become absent, this signals potential magnesium toxicity, requiring immediate dose reduction or discontinuation and possibly administration of calcium gluconate as an antidote [ 1 ]
From the Research
Effects of Magnesium on Deep Tendon Reflexes
- Magnesium therapy can affect deep tendon reflexes, with high doses potentially leading to a loss of deep tendon reflexes 2, 3, 4, 5.
- The loss of deep tendon reflexes is often used as a guide to magnesium therapy, with serum levels above 5.5 meq/liter typically avoided 3, 4.
- Deep tendon reflexes are an important indicator of magnesium toxicity, and monitoring them is crucial when administering magnesium therapy, particularly in patients with renal insufficiency 2, 3, 4, 5.
- The relationship between magnesium and deep tendon reflexes is also relevant in the context of lumbar spine diseases, where deep tendon reflexes can be used as a diagnostic tool 6.
Clinical Implications
- Magnesium sulphate therapy can cause reduced tendon reflexes, as observed in 14 (3.1%) patients in a study of women with pre-eclampsia and eclampsia 5.
- The use of deep tendon reflexes in diagnosing lumbar spine diseases highlights the importance of considering the effects of magnesium on these reflexes in clinical practice 6.
- Magnesium therapy should be carefully monitored, with attention to deep tendon reflexes, serum magnesium levels, and other indicators of magnesium toxicity 2, 3, 4, 5.