How should primidone be managed during the peri‑operative period and anesthesia?

Primidone and Anesthesia Management

Continue primidone through the morning of surgery, including on the day of operation, to prevent seizure breakthrough and withdrawal complications. 1, 2

Preoperative Management

Primidone should NOT be discontinued perioperatively. The 2021 SPAQI consensus guidelines clearly recommend continuing anticonvulsants through the perioperative period 1. Abrupt discontinuation risks:

• Seizure breakthrough during the vulnerable perioperative period
• Withdrawal symptoms that compound surgical stress
• Loss of therapeutic steady-state levels that take weeks to re-establish

Day of Surgery Protocol

• Administer the morning dose with a small sip of water 2-4 hours before surgery
• Document the exact dose and timing for the anesthesia team
• Ensure therapeutic levels are maintained (5-12 mcg/mL) 2

Critical Anesthetic Considerations

Drug Interactions - Major Concern

Primidone significantly potentiates local anesthetic neurotoxicity 3. This is the most clinically relevant perioperative interaction:

• Primidone markedly enhances local anesthetic-induced convulsions
• Shortens latency to toxicity and increases mortality risk
• Applies to both procaine and lidocaine-type local anesthetics

Practical implications:

• Use reduced doses of local anesthetics for regional blocks and infiltration
• Monitor closely for early signs of local anesthetic systemic toxicity (LAST)
• Have lipid emulsion immediately available
• Consider alternative regional techniques or lower concentrations

Anesthetic Agent Selection

• Avoid phenytoin and other enzyme inducers that may interact unpredictably
• Primidone is metabolized to phenobarbital - expect cross-tolerance effects 4
• Patients may require higher doses of anesthetic agents due to enzyme induction
• Use depth of anesthesia monitoring to guide dosing

Intraoperative Management

Multimodal analgesia is essential to minimize reliance on any single agent:

• Regional anesthesia with cautious local anesthetic dosing (see above)
• Non-opioid adjuncts: acetaminophen, NSAIDs (if not contraindicated)
• Ketamine in subanesthetic doses
• Dexmedetomidine for opioid-sparing effects

Monitor for:

• Prolonged effects of anesthetic agents (enzyme induction may be variable)
• Signs of local anesthetic toxicity at lower-than-expected doses
• Adequate seizure prophylaxis maintenance

Postoperative Management

Immediate Recovery

• Resume primidone as soon as oral intake tolerated - typically within 4-6 hours post-procedure
• If NPO status prolonged >24 hours, consider:
  • Nasogastric administration of crushed tablets
  • Consultation with neurology for alternative anticonvulsant coverage
  • IV phenobarbital as bridge therapy (cross-tolerance exists) 4

Pain Management Strategy

Avoid over-reliance on local anesthetic techniques given the enhanced neurotoxicity risk 3. Instead:

• Systemic opioids at standard doses (primidone doesn't significantly affect opioid pharmacology)
• Scheduled acetaminophen and NSAIDs
• Regional techniques acceptable but with dose reduction of local anesthetics
• Consider epidural or continuous peripheral nerve blocks with reduced local anesthetic concentrations

Common Pitfalls to Avoid

1. DO NOT stop primidone "to simplify perioperative management" - seizure risk outweighs any perceived benefit 5

2. DO NOT use standard local anesthetic doses for regional blocks - reduce by 25-30% and monitor vigilantly 3

3. DO NOT assume cross-coverage from other perioperative medications - primidone has unique pharmacology requiring continuation 2

4. DO NOT delay resumption postoperatively - even 24-48 hours of missed doses increases seizure risk significantly 5

Special Circumstances

Emergency Surgery

• Give primidone dose even if fasting guidelines violated (seizure risk > aspiration risk in this context)
• Document clearly for anesthesia team

Prolonged NPO Status

• Coordinate with neurology by postoperative day 1 if oral intake not resumed
• Consider phenobarbital IV as bridge (cross-tolerance minimizes adverse effects) 4

The evidence strongly supports continuation of primidone throughout the perioperative period, with the critical caveat that local anesthetic dosing must be reduced due to enhanced neurotoxicity risk.