How do I safely convert or adjust gabapentin dosages?

Gabapentin to Pregabalin (Lyrica) Conversion

Convert gabapentin to pregabalin using an approximate 6:1 ratio, then reduce the calculated pregabalin dose by 25-50% to account for incomplete cross-tolerance between gabapentinoids.

Conversion Algorithm

Step 1: Calculate Total Daily Gabapentin Dose

• Determine the patient's current total daily gabapentin dose in mg/day 1, 2
• Example: Patient taking gabapentin 600 mg three times daily = 1800 mg/day total

Step 2: Apply the Conversion Ratio

• Use a 6:1 conversion ratio (gabapentin:pregabalin) 1
• Divide total daily gabapentin dose by 6 to get equivalent pregabalin dose
• Example: 1800 mg gabapentin ÷ 6 = 300 mg pregabalin

Step 3: Reduce for Incomplete Cross-Tolerance

• If pain was well-controlled on gabapentin: Reduce the calculated pregabalin dose by 25-50% 3
• If pain was poorly controlled on gabapentin: May use 100% of calculated dose or increase by 25% 3
• Example: 300 mg pregabalin reduced by 25-50% = 150-225 mg pregabalin daily

Step 4: Divide into Appropriate Dosing Schedule

• Pregabalin is typically dosed twice daily (BID) or three times daily (TID) 3
• Example: 150 mg pregabalin = 75 mg BID

Critical Dosing Considerations

Renal Impairment

• Both gabapentin and pregabalin require mandatory dose reduction based on creatinine clearance 1, 2
• Calculate CrCl using Cockcroft-Gault equation before conversion 2
• Adjust final pregabalin dose according to renal function 3

Elderly Patients

• Start at the lower end of the calculated dose range (use 50% reduction rather than 25%) 3, 1
• Elderly patients have higher risk of falls, dizziness, and sedation with gabapentinoids 3, 4

Titration After Conversion

• Monitor closely for 3-7 days after conversion 1, 5
• Titrate pregabalin upward by 75-150 mg increments every 3-7 days if needed for pain control 1
• Maximum pregabalin dose is typically 300-600 mg/day (150-300 mg BID) 3

Common Pitfalls to Avoid

Do Not Use 1:1 Conversion

• Pregabalin is approximately 6 times more potent than gabapentin on a mg-per-mg basis 1
• Direct 1:1 conversion will result in severe overdosing and increased adverse effects

Do Not Forget Cross-Tolerance Reduction

• Even though both are gabapentinoids, incomplete cross-tolerance exists 3
• Failure to reduce dose by 25-50% increases risk of sedation, dizziness, and peripheral edema 3

Monitor for Synergistic Sedation

• Gabapentinoids have synergistic sedative effects with opioids 3
• If patient is on concurrent opioids, use extra caution and consider larger dose reduction (50% rather than 25%) 3
• Risk of altered mental status increases at pregabalin doses ≥200 mg/day in vulnerable populations 4

Taper Gabapentin Appropriately

• Do not abruptly discontinue gabapentin 2
• Taper over minimum 1 week to avoid withdrawal symptoms 1, 2
• Can overlap with pregabalin initiation during taper period

Practical Example

Patient on gabapentin 1200 mg TID (3600 mg/day total) with good pain control:

1. Calculate equivalent: 3600 mg ÷ 6 = 600 mg pregabalin
2. Reduce by 25-50%: 600 mg × 0.5 = 300 mg pregabalin daily
3. Divide into BID dosing: 150 mg pregabalin twice daily
4. Taper gabapentin over 1 week while initiating pregabalin 2

Patient on gabapentin 900 mg/day with poor pain control:

1. Calculate equivalent: 900 mg ÷ 6 = 150 mg pregabalin
2. Use 100% of dose (pain poorly controlled): 150 mg pregabalin daily
3. Divide into BID dosing: 75 mg pregabalin twice daily
4. Plan to titrate upward by 75-150 mg every 3-7 days as tolerated 1, 5