Anticonvulsant agents in eclampsia

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"

NICE have given guidance concerning the use of anticonvulsants in preeclampsia:

• if a woman in a critical care setting who has severe hypertension or severe pre-eclampsia has or previously had an eclamptic fit, give intravenous magnesium sulphate
  
  
• consider giving intravenous magnesium sulphate to women with severe pre-eclampsia who are in a critical care setting if birth is planned within 24 hours
  
  
• consider the need for magnesium sulfate treatment, if 1 or more of the following features of severe pre-eclampsia is present:
  • ongoing or recurring severe headaches
  • visual scotomata
  • nausea or vomiting
  • epigastric pain
  • oliguria and severe hypertension
  • progressive deterioration in laboratory blood tests (such as rising creatinine or liver transaminases, or falling platelet count
    
    
• use the Collaborative Eclampsia Trial regimen for administration of magnesium sulphate:
  • loading dose of 4 g should be given intravenously over 5 minutes, followed by an infusion of 1 g/hour maintained for 24 hours
  • recurrent fits should be treated with a further dose of 2-4 g given intravenously over 5 to 15minutes
    
    
• NICE state that clinicians should not use diazepam, phenytoin or other anticonvulsants as an alternative to magnesium sulfate in women with eclampsia

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.
4. NICE (June 2019). Hypertension in pregnancy - the management of hypertensive disorders during pregnancy