What labs should be ordered for a patient transitioning from Keppra (levetiracetam) to Zonisamide while on Lamictal (lamotrigine)?

Laboratory Monitoring for a Patient on Lamictal, Transitioning from Keppra to Zonisamide

For a patient with new onset seizure disorder on lamotrigine (Lamictal) and transitioning from levetiracetam (Keppra) to zonisamide, you should order a complete blood count, liver function tests, and renal function tests to monitor for potential adverse effects and ensure safe medication management.

Essential Laboratory Tests

Baseline Tests

• Complete blood count (CBC) with differential to monitor for hematologic abnormalities that can occur with antiepileptic drugs 1
• Comprehensive metabolic panel including:
  • Liver function tests (AST, ALT, bilirubin) to monitor for hepatotoxicity 1
  • Renal function tests (BUN, creatinine) as zonisamide is primarily excreted by the kidneys 1
  • Electrolytes to assess for imbalances that may occur with antiepileptic medications 1

Medication-Specific Monitoring

For Lamotrigine (Lamictal)

• Liver function tests are particularly important as lamotrigine can cause hepatic adverse effects 1
• No specific serum drug level monitoring is required for routine use, but may be considered in special circumstances such as suspected toxicity or non-compliance 1
• Monitor for signs of rash, which can be a serious adverse effect of lamotrigine 1

For Zonisamide

• Renal function tests are critical as zonisamide is primarily eliminated by the kidneys 1, 2
• Bicarbonate levels to monitor for metabolic acidosis, which can occur with zonisamide 1
• Consider baseline urinalysis to monitor for kidney stones, which is a potential adverse effect of zonisamide 1

Follow-up Monitoring Schedule

• Initial follow-up labs should be performed 2-4 weeks after starting zonisamide 1
• Subsequent monitoring should occur every 3-6 months during the first year of treatment 1
• After stabilization, laboratory monitoring can be performed every 6-12 months 1

Drug Interaction Considerations

• No clinically significant pharmacokinetic interactions have been reported between lamotrigine and zonisamide at steady state, so no specific monitoring is required for this combination 3
• Levetiracetam has minimal drug interactions and does not induce or inhibit liver enzymes, making the transition to zonisamide less complicated from a drug interaction perspective 2
• Unlike some other antiepileptic drugs (like carbamazepine, phenytoin, or phenobarbital), neither lamotrigine, levetiracetam, nor zonisamide are strong enzyme inducers, which simplifies monitoring requirements 1, 2

Additional Considerations

• Weight monitoring is recommended as zonisamide can cause weight loss 1
• Monitor for neuropsychiatric symptoms, as both lamotrigine and zonisamide can cause mood changes, depression, or anxiety 1
• For female patients of childbearing potential, consider pregnancy testing before initiating treatment, as antiepileptic medications may have teratogenic effects 1, 4

Common Pitfalls to Avoid

• Failing to establish baseline values before starting zonisamide, which makes it difficult to attribute abnormalities to the medication 1
• Not monitoring renal function in patients on zonisamide, which can lead to drug accumulation and toxicity 1
• Overlooking the need for more frequent monitoring during the transition period between medications 1
• Not educating the patient about potential side effects that should prompt immediate medical attention, such as rash with lamotrigine 1