OTC wormers any good?

I want to worm in between interceptor doses. The lady at Novartis says this is perfectly fine and safe. I called the vet and of course they say that no OTC wormer will even work and I have to get strongid from them. I don't mind getting it from them but the vet is about 35 min away so if there's an OTC option that actually works (on roundworms for the most part) it might be more convenient. I would like to worm right in between interceptor doses (so she wouldn't go more than 2 weeks or so without a worming) until 6 mos or so (these roundworms still have me freaked out if you can't tell already). My only local options are a local pet store (j&k-not sure if that's a chain or what but there are several in this area) and walmart, plus Rural King which is a farm supply store. I've no problem with ordering it online. thanks!