Well, it really does matter what ailment you're trying to treat. Fenbendazole (panacur) is probably the most frequently used, due to the prevalence of parasitic worms. However, consider that Asprin is the most commonly used human medicine worldwide. Asprin is also the drug that kills the most people worldwide. I AM NOT TRYING TO SAY THAT PANACUR IS UNSAFE, BUT THAT ASPRIN IS MUCH MORE DANGEROUS THAN PANACUR. YOU NEED TO TREAT SPECIFIC CONDITIONS WITH SPECIFIC DRUGS, NOT JUST WHAT HAPPENS TO BE COMMON (like asprin.) Metronidazole would come in second, as far as commonly used frog meds.