Sulfa and Furan Drugs
Sulfa and furan drugs do not treat fish diseases very well. They should be thought of as antiseptics which have limited bacteriostatic actions when dissolved in the water column of an aquarium. They will stop the transmission of bacteria from one fish to another fish. They are far more effective when used as bath treatments.
Sulfa and Furan Drugs in More Depth
Sulfaguanidine, sulfathiazole, sulfamethazine and sulfacetamide are all what are called “sulfa drugs”. Mardel Maracyn Plus is a combination of two anti-bacterial drugs, sulfaguanidine and trimethoprim (trimethoprim is an antibiotic with an action which is very similar to furans). SeaChem SulfaPlex (Sulfathiazole) is a sulfa drug. API Triple Sulfa (Sulfathiazole, Sulfamethazine and Sulfacetamide) is a sulfa combination.
“Furans” include nitrofurantoin, nitrofurazone and furazolidone. Bifuran is nitrofurazone and furazolidone. SeaChem Focus is “polymer bound” nitrofurantoin. Sulfa and furans have very similar properties,
Furans supposedly “effectively treats many gram-positive and gram-negative bacterial diseases like aeromonas and columnaris quickly and easily”. Seachem Sulfaplex, “Treats Many Bacterial, Fungal and Protozoan Infestations“. API Triple Sulfa™ Powder “contains three sulfa medications to effectively treat bacterial infections such as hemorrhagic septicemia (blood streaks in fins and body and localized swelling), bacterial gill disease, fin & tail rot, cotton mouth disease, body slime and eye cloud for both fresh and saltwater fish“.
Antibiotics like Kanamycin are very selective in what they kill. They kill only bacterial cells, not fish cells. They can only kill so called “higher order organisms”, such as fish and humans, by something called “organ overload”. Too heavy a dose of antibiotic over too long a time CAN overload the metabolic breakdown pathways in the liver and result in liver failure, which, in turn, kills the fish or the human. But it takes a sizable overload, well beyond the normal therapeutic level of antibiotic. So antibiotics are safe if added to fish food.
But furans and sulfa drugs CAN kill the fish if ingested in overdoses. So one cannot put sulfa drugs or furans into the food for fish unless one can closely somehow control the amount in the food that the fish ingest. So, with furans or sulfa drugs, you can’t actually treat any bacterial diseases which have started to appear in the fish as those bacterial diseases are internal, inside the fish. Furans and sulfa drugs do have limited use in the water column, stopping the transmission of pathogenic bacteria. And they are safer than most antiseptics as the level at which they inhibit the bacteria is much lower than the levels at which they kill fish.
Note furans will kill plants. Many have treated their planted aquariums with furans with disastrous results.
There is one way to safely use furans and sulfa drugs which seems to be very effective. If one has fish that have a bacterial disease make up a bath with a sizable dose of the furans or sulfa drugs. Put the fish in the heavily dosed water for one hour and only one hour. Then return the fish to an aquarium. Repeat this once every 24 hours, no more. Studies show this can reduce mortalities from bacterial infections like columnaris by 10% to 80%, depending on the bacteria and the fish.
This bath treatment achieves therapeutic levels of the furans and the sulfa drugs in the fish for short periods of time. Both furans and sulfa drugs are soluble in both fat and in water. So they do seem to pass into the fish through the skin and gills when administered in a bath. Both classes of drugs are then very rapidly removed by the kidneys of the fish. The damage to the fish during this “pulse” is low enough that the fish survive. And limited numbers of the bacteria in the fish are also killed. But the baths typically do not “cure” all the fish.
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