It really depends on what form of copper and the amount contained in the medication, especially when dealing with a scaleless invert or SFE. Either way, what's done is done, and now I think you need to focus on how to proceed.
If you believe there's a chance copper will harm your SFE, and i think it may, there is a solution that will help. You can purchase a Kent Regenerable Toxic Metal Sponge (about $18 at LFS). It removes copper, lead, mercury and other metals from your tank. You put the beads (bottle contains tons of small "beads") in a filter sock or polyester bag and place it in an area of high water flow.
Back in my younger days, I overdosed a marine tank with a copper-based medication. When I found out the next day this was harmful, I pulled the eel out and ran the Kent Sponge for a while, then added the eel back in, and continued to run a PH through the sponge for months. Never found trace of copper in my tank, and never noticed harmful results (pods, worms, inverts, SFE - all seemed healthy and unaffected).