First-Line Treatment for Seizures in Eclampsia
Magnesium sulfate is the first-line treatment for seizures in eclampsia, administered as a 4-5 g intravenous loading dose over 5-15 minutes, followed by a maintenance infusion of 1-2 g/hour. 1, 2
Initial Management Algorithm
Immediate Seizure Control
- Administer magnesium sulfate 4 g IV over 5-15 minutes as the loading dose 1
- Alternative loading regimen: 5 g intramuscularly into each buttock (10 g total IM) if IV access is delayed 3
- Magnesium sulfate is superior to diazepam and phenytoin for preventing recurrent eclamptic seizures 4, 5
Maintenance Therapy
- Continue magnesium sulfate at 1-2 g/hour by controlled infusion pump 1, 2
- Alternative IM maintenance: 5 g IM every 4 hours in alternating buttocks 2, 6
- Therapeutic serum magnesium levels for seizure control range from 2.5-7.5 mEq/L (or 1.8-3.0 mmol/L) 2, 6
Mechanism and Onset of Action
- Magnesium prevents seizures by blocking neuromuscular transmission and decreasing acetylcholine release at the motor end-plate 2
- IV administration provides immediate anticonvulsant effect lasting approximately 30 minutes 2
- IM administration has onset within 1 hour and persists for 3-4 hours 2
Critical Monitoring Requirements
Essential Safety Parameters
- Monitor deep tendon reflexes (patellar reflex) - loss occurs at 3.5-5 mmol/L, indicating impending toxicity 2, 6
- Assess respiratory rate continuously - respiratory paralysis occurs at 5-6.5 mmol/L 2, 6
- Monitor urine output - magnesium is excreted solely by kidneys; renal insufficiency leads to toxicity 2, 6
- Check serum magnesium concentrations when available 6
Toxicity Thresholds
- Loss of deep tendon reflexes: 3.5-5 mmol/L 6
- Respiratory paralysis: 5-6.5 mmol/L 6
- Altered cardiac conduction: >7.5 mmol/L 6
- Cardiac arrest: >12.5 mmol/L 2, 6
Concurrent Blood Pressure Management
Severe Hypertension Treatment (≥160/110 mmHg)
- Blood pressure ≥160/110 mmHg lasting >15 minutes requires immediate antihypertensive treatment 1
- First-line IV agents: labetalol or IV nicardipine 1
- First-line oral agent: nifedipine (extended-release) 1, 7
- IV hydralazine is a second-line option 1
Critical Drug Interaction
- Do NOT administer magnesium sulfate concomitantly with calcium channel blockers (nifedipine) due to risk of severe hypotension from synergism 1, 7
- If both agents are needed, stagger administration and monitor blood pressure closely 1
Recurrent Seizure Management
- If seizures recur despite initial loading dose, administer additional 2 g magnesium sulfate IV over 5 minutes 1
- Repeat 5 g IM dose if using intramuscular regimen 3
- Most seizures terminate after the initial loading dose; only 2 of 133 patients required repeat dosing in one series 3
Important Clinical Pitfalls
Contraindications and Precautions
- Avoid prolonged administration beyond 5-7 days in pregnancy - causes fetal hypocalcemia, skeletal demineralization, osteopenia, and neonatal fractures 2
- Use with extreme caution in renal insufficiency - magnesium accumulation leads to toxicity 2
- Premature neonates are at particular risk for aluminum toxicity from magnesium sulfate preparations 2
Medications to Avoid
- Methyldopa should NOT be used for urgent blood pressure reduction in eclampsia 1
- Diuretics should be avoided - plasma volume is already reduced in pre-eclampsia 1
Antidote for Magnesium Toxicity
- Administer IV calcium (calcium gluconate or calcium chloride) to antagonize central and peripheral effects of magnesium poisoning 2
- Keep calcium readily available at bedside during magnesium sulfate administration 5