I used to take Gabapentin for chronic pain, and I'm pretty sure that I started out at 150 mg 3 times/day. I ended up going up to 800 mg 3 times/day, but it can take a while for your body to adjust to the medication.

I'd ask your doctor if there's any reason why you shouldn't drop your dosage to 150 mg 3x/day and then increase gradually. If you have tablets, you can just break them in half.

The starting dose info. that I saw when I did a web search said start at 300 mg 3 times/day for epilepsy and listed 10-15 mg/kg of body weight 3 times/day as a suggested starting dose for other conditions.