Nikki and Lee
There are no such test kits but here are other means like ICP, etc. This is not only the issue with drugs but any type of colored water. Many "drugs" used in fish treatment color the water. Yellow water mixed with the green, say that green from a Salicylate test kit, is going to produce a funny color. Same think if mixing yellow with a Phenol red test kit. Then there is the other issue, does the drug interred with the ammonia test kit. You are better off with a SeaChem Alert, which adsorbs ammonia onto a card, where the chemical reaction changes the color of the card indicating the amount of ammonia.
Some "drugs" do or will treat fungus. For example Methylene Blue, a light molecular weight organic- inorganic dye, C16H18ClN3S, works well. It is also often a determining indicator for fungus as it adsorbs the blue dye and stains the fungus blue where bacteria do not.
There are true fungicides that work great in seawater but must be gotten from a Vet, such as Griesofulvin but at a cost of 125mg /30 Tablets @ $ 74.95