--taking those meds will conflict with the injection; more likely they would work in synergy.

Stopping any of those meds suddenly, though, would NOT be a good idea--the rebound effect might make the pain worse, and bring with it other wtihdrawl effects. Almost all meds must be tapered off gradually, to give the body time to adjust. The anti-seizure drugs (i.e, Neurontin, Topamax, Lyrica) in particular should be tapered off slowly, as there is the possibility of rebound seizures--the previously depressed, and therefore, likely "upregulated" central nervous system signal propogation might be overwhelming if the "pharmaceutical brake" is suddenly removed.