In my experience all the over the counter stuff is the same.... garbage. The doses are so low for it to be sold over the counter that it doesn't even get rid of the worms.

If the vet has not seen the animals before you will most likely have to bring them in for an exam as well. If you provide your vet with your animals previous vet records and they are current on everything then some vets will just allow you to bring in a fecal sample and some might even prescribe it over the phone.

Even if for some reason you don't need a vet for this problem, please re-search them in your area anyways & get an account set up with a decent one asap. You never know if an emergency pops up.