Pregabalin 25mg is NOT Equivalent to Gabapentin 300mg
There is no established dose equivalence between pregabalin 25mg and gabapentin 300mg, and these doses represent vastly different positions in their respective therapeutic ranges. Pregabalin 25mg is below any recommended starting dose, while gabapentin 300mg is a standard initial dose.
Why Direct Dose Equivalence is Problematic
The two medications cannot be directly compared on a milligram-to-milligram basis due to fundamental pharmacokinetic differences:
- Pregabalin has linear pharmacokinetics with >90% bioavailability regardless of dose, making absorption predictable and dose-proportional 1, 2
- Gabapentin has nonlinear, saturable absorption with bioavailability dropping from 60% at 900mg/day to 33% at 3600mg/day, making its pharmacokinetics less predictable 1, 2
- Pregabalin is absorbed more rapidly (peak at 1 hour) compared to gabapentin (peak at 3-4 hours) 2
Established Dosing Ranges
Pregabalin Standard Dosing
- Starting dose: 75mg twice daily or 50mg three times daily (150mg/day total) 1, 3
- Standard therapeutic dose: 300mg/day (150mg twice daily or 100mg three times daily) 1, 3
- Maximum dose: 600mg/day 1, 3
Gabapentin Standard Dosing
- Starting dose: 100-300mg at bedtime or 300mg once daily 1, 4
- Standard therapeutic dose: 1800-3600mg/day in three divided doses 1, 4
- Maximum dose: 3600mg/day 1, 4
Approximate Conversion Ratios from Clinical Evidence
When transitioning between medications, pharmacokinetic modeling suggests the following approximate ratios:
- Gabapentin 900mg/day ≈ Pregabalin 150mg/day 5
- Gabapentin 1800mg/day ≈ Pregabalin 300mg/day 5
- Gabapentin 3600mg/day ≈ Pregabalin 600mg/day 5
This suggests an approximate 6:1 ratio (gabapentin:pregabalin) at therapeutic doses 5. Using this ratio, pregabalin 25mg would theoretically correspond to gabapentin 150mg, not 300mg.
Clinical Efficacy Comparison
- For neuropathic pain, pregabalin 450mg/day appears to reduce pain comparably to the predicted maximum effect of gabapentin 2
- In head-to-head comparison for chronic sciatica, gabapentin (400-800mg three times daily) showed superior pain reduction compared to pregabalin (150-300mg twice daily) with fewer adverse events 6
- Pregabalin may have higher intrinsic potency than gabapentin, with significant antiepileptic effects at 150-600mg/day 7
Critical Clinical Pitfall
Pregabalin 25mg is below the minimum effective starting dose of 50mg three times daily (150mg/day total) 1, 3. This dose would not be expected to provide therapeutic benefit for any approved indication and represents an inadequate trial of pregabalin therapy.
Recommended Transition Approach
If transitioning from gabapentin 300mg/day to pregabalin: