Never use furan?
It's an antibiotic; and is not all that strong. It has a nitrogenous compound in it that has been linked by some tests to cancer in mice at high doses. these doses are not what we treat fish at, and human exposure at those levels are quite well unfeasible. but by all means, use gloves if you have to, but without a prescription, it's all you can use.
Do not be afraid of it; just use it correctly, and like any other medication - handle it with care.