Can leucovorin (folinic acid) induce seizures, and what is the recommended management if a seizure occurs in a patient receiving leucovorin rescue after high-dose methotrexate?

Leucovorin and Seizures

Leucovorin (folinic acid) itself does not directly induce seizures; however, seizures have been reported rarely in cancer patients receiving leucovorin, usually in association with fluoropyrimidine administration and most commonly in those with CNS metastases or other predisposing factors, though a causal relationship has not been established 1.

Context: Leucovorin as Rescue Therapy

Leucovorin is primarily used as rescue therapy after high-dose methotrexate (HD-MTX) to mitigate systemic toxicity, particularly myelosuppression and hepatotoxicity 2. The key principle is that leucovorin does not cross the blood-brain barrier in amounts sufficient to interfere with methotrexate's effect in the CSF 2, making it safe for use in patients receiving intrathecal or high-dose systemic methotrexate.

Seizure Risk Profile

Direct Seizure Causation

• Seizures are not a recognized direct toxicity of leucovorin itself
• When seizures occur in patients receiving leucovorin, they are typically associated with:
  • Concurrent fluoropyrimidine (5-FU) therapy 1
  • Underlying CNS metastases 1
  • Other predisposing neurological factors 1
  • Syncope may also occur in similar contexts 1

Methotrexate-Related Neurotoxicity

The more relevant concern is methotrexate-induced neurotoxicity, which can manifest as:

• Acute arachnoiditis (after intrathecal MTX) 3
• Subacute encephalitis (after IV high-dose MTX) 3
• Leukoencephalopathy (particularly with abnormal CSF flow or concurrent CNS radiation) 2
• Aseptic meningitis (10-50% with intrathecal MTX) 4
• Acute cerebellar syndrome 4
• Transverse myelopathy 4

Critically, adequate leucovorin rescue prevents methotrexate-induced neurotoxicity without compromising therapeutic efficacy 5, 6.

Management of Seizures in Patients Receiving Leucovorin Rescue

If Seizure Occurs During HD-MTX/Leucovorin Treatment:

1. Immediate seizure management:

   • Administer standard antiepileptic treatment 4
   • Ensure airway protection and supportive care
   • Do NOT discontinue leucovorin rescue prematurely

2. Assess methotrexate levels and rescue adequacy:

   • Measure serum methotrexate concentration immediately 1
   • Check serum creatinine and renal function 1
   • Verify leucovorin dosing has been appropriate for MTX levels

3. Adjust leucovorin based on MTX levels 1:

   • If MTX level >0.2 μmol/L at 72 hours: Continue leucovorin 15 mg IV q6h until MTX <0.05 μmol/L
   • If MTX level ≥50 μmol/L at 24h or ≥5 μmol/L at 48h: Escalate to leucovorin 150 mg IV q3h until MTX <1 μmol/L, then 15 mg q3h until <0.05 μmol/L
   • Continue hydration and urinary alkalinization (pH ≥7.0) 1

4. Investigate alternative causes:

   • Obtain brain imaging (MRI preferred) to evaluate for:
     • CNS metastases
     • Posterior reversible encephalopathy syndrome (PRES) if on concurrent agents
     • Leukoencephalopathy
     • Acute cerebellar changes
   • Consider lumbar puncture if aseptic meningitis suspected (but only after ruling out increased ICP) 4
   • Check for drug interactions that may elevate MTX levels (phenytoin, NSAIDs, sulfonamides) 2

5. Do NOT administer leucovorin intrathecally 1:

   • Intrathecal leucovorin may be harmful or fatal 1
   • This is a critical safety warning even in cases of intrathecal MTX overdose

Prevention of MTX-Related Neurotoxicity

The evidence strongly supports that adequate leucovorin rescue prevents neurotoxicity 5, 7, 6:

• Standard rescue: 15 mg (approximately 10 mg/m²) IV/PO q6h for 10 doses starting 24 hours after beginning MTX infusion 1
• Timing is crucial: Rescue started at 24-36 hours is safe; delays beyond 42 hours increase neurotoxicity risk unless MTX levels remain consistently low 5, 7
• Dose adequacy: Studies using 105 mg/m² leucovorin starting at 30-36 hours after MTX (5-6 g/m²) showed no neurotoxicity even after mega-doses of MTX 5, 7

Common Pitfalls to Avoid

1. Under-rescue: Insufficient leucovorin dosing is the primary cause of preventable MTX neurotoxicity 5, 6
2. Delayed rescue initiation: Starting leucovorin >42 hours after MTX significantly increases toxicity risk 7
3. Premature discontinuation: Continue rescue until MTX level <0.05 μmol/L, not based on arbitrary time points 1
4. Intrathecal administration: Never give leucovorin intrathecally 1
5. Over-rescue concerns: Higher leucovorin doses do NOT rescue leukemia cells or compromise cure rates 6, 8

Special Considerations

• Renal impairment: Requires more aggressive leucovorin rescue and closer monitoring 1
• Third-space fluid accumulation: May delay MTX elimination, necessitating prolonged rescue 1
• Concurrent medications: Phenytoin (an antiepileptic) actually increases MTX toxicity through protein displacement 2—use alternative antiepileptics if chronic therapy needed

In summary: If seizures occur during leucovorin rescue after HD-MTX, treat the seizure acutely, ensure leucovorin rescue is adequate based on MTX levels (not arbitrary timing), investigate alternative causes including CNS disease, and never give leucovorin intrathecally.