Dan has given great advice on using vitamins and minerals to amphibians. I am a former amphibian keeper at the Omaha Zoo. We took care of many species of amphibians that are on the critically endangered list, including the Wyoming toad and the Puerto Rican crested toad. Vitamin A was used to prevent STS (short tongue syndrome) - where the toad has difficulty eating and getting around. Our protocol was to use liquid vitamin A and administered one drop weekly on the toad's back. I don't know how difficult it is to get the liquid form of vitamin A, but it sure makes it a lot easier. Good luck!