Maybe the doc didn't mention it, but the Lyrica & gabapentin have to be totaled together to see what your total intake is. that's the reason for the equivalency.
If you are taking, say 3000 mgs of gabapentin and add Lyroca, you have to back off of the gabapentin to still equal the 3000mgs.
When I switched to Lyrica completely, I had to have a titration chart of backing off gabapentin and adding Lyrica, in increments of 50mg of Lyrica, until I had completely replaced the 4200mgs of gabapentin with the Lyrica. I started with 150mgs of Lyrica and reduced 900mgs of the gabapentin. It took about 10 days.