I am passing this information on in case you have day time itch. Gabapentin reaches its peak effectiveness after you have taken it for 4 weeks. The effect of one dose will only last 6-8 hours, that is why I take 100mg three times a day.
The reported half-life (the time it takes for 50% of the drug to be metabolized) is 5 to 7 hours, which necessitates a dosing frequency of 3 to 4 times daily for it to be effective.
It is great that antihistamines during the day appear to be helping you, I was not so fortunate:)