How to manage hyponatremia induced by Eptoin (Phenytoin)?

Management of Phenytoin-Induced Hyponatremia

The most effective approach to managing phenytoin (Eptoin)-induced hyponatremia is to discontinue the medication and switch to an alternative antiepileptic drug with lower risk of hyponatremia, such as lamotrigine or gabapentin, while carefully correcting sodium levels based on symptom severity and chronicity.

Assessment and Diagnosis

• Phenytoin (Eptoin) is among several antiepileptic drugs known to cause hyponatremia, with a moderate association (adjusted OR 4.83) for hospitalization due to hyponatremia with newly initiated treatment 1
• Initial evaluation should include serum and urine osmolality, urine electrolytes, and assessment of extracellular fluid volume status to determine the underlying mechanism of hyponatremia 2
• Phenytoin-induced hyponatremia typically occurs through a syndrome of inappropriate antidiuretic hormone secretion (SIADH) mechanism 3, 4

Management Strategy Based on Symptom Severity

For Severe Symptomatic Hyponatremia (seizures, coma, severe neurological symptoms)

• Immediately administer 3% hypertonic saline with an initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 2
• Total correction should not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 2
• Consider ICU admission for close monitoring during treatment 2
• Discontinue phenytoin and replace with an alternative antiepileptic with lower risk of hyponatremia (lamotrigine or gabapentin) 1

For Mild to Moderate Symptomatic Hyponatremia

• Implement fluid restriction to 1-1.5 L/day 2
• Discontinue phenytoin and switch to an alternative antiepileptic drug 3, 1
• Monitor serum sodium levels every 4-6 hours initially 2
• Consider oral sodium supplementation if fluid restriction alone is insufficient 2

Alternative Antiepileptic Medications

• Lamotrigine has the lowest association with hyponatremia (adjusted OR 1.67) and should be considered as a first-line alternative 1
• Gabapentin also shows relatively low risk (adjusted OR 1.61) and may be suitable as an alternative 1
• Avoid switching to carbamazepine, oxcarbazepine, or levetiracetam as these have stronger associations with hyponatremia 1

Monitoring and Follow-up

• For severe hyponatremia: monitor serum sodium every 2 hours during initial correction 2
• For mild to moderate hyponatremia: check sodium levels daily until stable 2
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) which typically occur 2-7 days after rapid correction 2

Special Considerations

• Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require more cautious correction (4-6 mmol/L per day) due to higher risk of osmotic demyelination syndrome 2
• If overcorrection occurs, consider relowering with electrolyte-free water or desmopressin 2
• "Re-challenge" with phenytoin should be avoided by informing the patient and caregivers about this adverse effect 3

Common Pitfalls to Avoid

• Failing to recognize drug-induced hyponatremia as the cause and continuing the offending medication 3
• Correcting sodium too rapidly (>8 mmol/L in 24 hours), which can lead to osmotic demyelination syndrome 2
• Inadequate monitoring during active correction of severe hyponatremia 2
• Using hypertonic saline in patients without severe symptoms 2
• Switching to another antiepileptic drug with high risk of hyponatremia 1

By following this approach, most patients with phenytoin-induced hyponatremia will recover fully with appropriate management 4.