What is the most serious toxic effect of magnesium sulfate in treating eclampsia?

In the context of treating eclampsia with magnesium sulfate, the most serious toxic effect is respiratory depression. Magnesium sulfate works as a central nervous system depressant, helping to prevent seizures by decreasing neuronal excitability. However, at higher serum magnesium levels, it can significantly depress respiratory function.

Respiratory depression is particularly critical because it can lead to inadequate ventilation and subsequently, hypoxia, which poses a serious risk to both the mother and the fetus. Monitoring respiratory rate and function is essential during magnesium sulfate administration to ensure that toxicity does not develop.

While loss of deep tendon reflexes, nausea and vomiting, and neonatal hypotonia can occur with magnesium sulfate treatment, they are generally considered less severe than respiratory depression. Loss of reflexes indicates significant magnesium toxicity but does not pose an immediate risk to life like respiratory depression does. Nausea and vomiting are more common side effects and are often manageable. Neonatal hypotonia is a concern for the baby, but it is a consequence rather than an acute toxic reaction that poses an immediate danger during treatment. Therefore, respiratory depression stands out as the most serious toxic effect in this scenario.