Keep and eye on this. If it continues a week after the meds have passed through the frog's system then their could be something else wrong. Very runny watery stool is indicative of a internal bacterial infection or protozoan infection, but as Lija said some medications can cause this.

Some vets will create a mixed suspension of Panacur and Metronidazole(Flagyl) so that while the Panacur kills the parasites the antibiotic Metronidazole prevents the frog from getting an infection and going into septic shock from the parasites dying and rotting inside the frog. Metronidazole kills many forms of bacterial and Protozoa.