Phenytoin in Eclampsia
Phenytoin should NOT be used as first-line treatment for eclampsia—magnesium sulfate is the only appropriate first-line agent, with phenytoin demonstrating unacceptably high seizure recurrence rates and inferior maternal and neonatal outcomes. 1
Evidence Against Phenytoin in Eclampsia
The American College of Obstetricians and Gynecologists explicitly recommends against using phenytoin as first-line therapy for eclampsia due to its markedly inferior efficacy compared to magnesium sulfate 1. The evidence is compelling:
Seizure Recurrence Rates
- Phenytoin shows a 17.5% seizure recurrence rate versus 0% with magnesium sulfate in randomized trials 1
- A prospective study of 68 women with eclampsia demonstrated an unacceptably high 26.5% seizure recurrence rate with phenytoin, with most recurrences (16 of 18 patients) occurring between the loading dose and first maintenance dose 2
- A large randomized trial (1,089 women) found 10 eclamptic convulsions in the phenytoin group versus zero in the magnesium sulfate group (P = 0.004) 3
Maternal and Neonatal Outcomes
- Magnesium sulfate reduces maternal mortality risk (though not reaching statistical significance in pooled data: RR 0.50,95% CI 0.24 to 1.05) 4
- Magnesium sulfate significantly reduces maternal complications including pneumonia (RR 0.44), need for ventilation (RR 0.68), and ICU admissions (RR 0.67) compared to phenytoin 4
- Neonatal outcomes favor magnesium sulfate, with fewer NICU admissions (RR 0.73) and fewer babies requiring prolonged intensive care (RR 0.77) 4
- A 2017 trial showed significantly lower convulsion rates with magnesium sulfate (P = 0.001) and higher one-minute Apgar scores 5
Why Magnesium Sulfate is Superior
Magnesium sulfate demonstrates 100% efficacy in preventing recurrent seizures in multiple randomized trials and is supported by the American College of Obstetricians and Gynecologists as the standard of care 1. A Cochrane systematic review of seven trials involving 972 women concluded that magnesium sulfate substantially reduces seizure recurrence (RR 0.34,95% CI 0.24 to 0.49) and that "the use of phenytoin should be abandoned" in eclampsia 4.
Critical Clinical Distinction
Eclampsia is NOT status epilepticus—the pathophysiology and treatment differ fundamentally 1, 6. While phenytoin has a role as a second-line agent in status epilepticus (with 84% efficacy after benzodiazepines) 6, this does NOT translate to eclampsia management. The cerebral vasospasm and endothelial dysfunction in eclampsia respond specifically to magnesium's unique mechanism of action 3.
Common Pitfall to Avoid
Do not confuse seizure management protocols: phenytoin's established role in neurologic status epilepticus does not apply to obstetric eclampsia 1, 6. Even when phenytoin achieves therapeutic levels in eclamptic patients, seizure recurrence remains unacceptably high 2.