Magnesium sulphate is now recognised as the treatment of choice for convulsions in eclampsia. There is evidence that it is a more effective anticonvulsant than diazepam in the treatment of eclampsia (1). Also magnesium sulphate makes further fits less likely than treatment with diazepam.

It is difficult to identify which patients are likely to have seizures from parameters such as degree of blood pressure elevation, proteinuria, and oedema.

Possible side effects of magnesium sulphate include:

• paralysis secondary to toxicity at the neuromuscular junction
• respiratory depression is preceded by slurring of speech, flushes, diplopia, nausea and loss of patellar reflexes. Treatment with magnesium sulphate may be complicated by respiratory arrest

Further evidence has revealed that magnesium sulphate reduces the risk of eclampsia in women with pre-eclampsia (2,3)

• a review (3) states that there is "robust evidence that, for women with pre-eclampsia, magnesium sulphate more than halves the risk of eclampsia (number needed to treat 100, 95% confidence interval 50 to 100) and probably reduces the risk of maternal death... However, no overall difference has been found in the risk of stillbirth or neonatal death. A quarter of women allocated magnesium sulphate had side effects, primarily flushing"

Reference:

1. Eclampsia Trial Collaborative group (1995). Which anticonvulsant for women with eclampsia? Lancet, 345, 1455-9.
2. The Magpie Trial Collaborative Group (2002). Do women with pre-eclampsia, and their babies, benefit from magnesium sulphate? The Magpie Trial: a randomised placebo-controlled trial. Lancet, 359, 1877-90.
3. BMJ. 2006 Feb 25;332(7539):463-8.