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TRIPLE SULFA (Sulfamerazine, Sulfamethazine, Sulfathiazole) & Other Sulfa Based Medications:
Sulfas are considered all anti-bacterials (antimicrobials).
These drugs are bacteriostatic, meaning they inhibit the growth of the bacteria but do not kill them.
Sulfas are generally most effective against aerobic gram-negative organisms, and occasionally effective against anaerobic gram negative bacteria, but are not reliable against aerobic gram-positive bacterium such as Streptococcus
More on: Streptococcus Eye Infection
Sulfa drugs arrest cell growth by inhibiting the synthesis of folic acid, a component required for growth by bacteria. Folic acid is a large molecule and is unable to enter bacterial cells, so the bacteria must synthesize the compound intracellularly.
Animal cells are unable to synthesize folic acid and it must be provided in the diet. For this reason sulfa drugs are not toxic to animal cells.
Sulfa drugs are among the oldest in the medicine, the first being a sulfonamide was trade named Prontosil dating back to experiments by Bayer in 1932.
For aquatic use Sulfa are often maligned by many aquarists as not effective or out of date, yet in reality Triple Sulfa often will work where other antibiotics fail and sometimes with less side effects as well (this is not to say Sulfas do not have side effects as they are somewhat toxic, producing blood abnormalities and kidney damage when indiscriminately used).
Sulfas also do not tend to be as sensitive to poor use (meaning not following the full treatment regimen).
USE: A relatively broad spectrum antibacterial medication; for fin and tail rot, mouth fungus and clamped or collapsed fins, Columnaris (mild to moderate infections ONLY), and hemorrhagic septicemia (although not effective to Aeromonas infections of the gut).
Triple Sulfa is very effective for basic Fin Rot infections with Pseudomonas as the bacterial pathogen. It is also useful for damaged fins caused by fin nipping.
An old standby that is still useful and can be used in combination with Malachite Green (especially effective in combination with MG at ˝ strength when treating Ich in scale less fish) or Acriflavin (do not combine with copper sulfate).
It is noteworthy that Sulfas are more effective at higher pH levels.
Sulfas can also be safely used with other mild broad spectrum parasite/fungal treatments to boost anti bacterial effectiveness,; a good example would be the Medicated Wonder Shell.
As well Triple Sulfa has minimal impact on nitrifying bio filters when used correctly
*Best not used concurrently with other antibiotics/antimicrobials, although use with chemical dyes such as malachite green is safe and even advised.
*Do not use with copper based medications
Trimethoprim is a bacteriostatic antibiotic effective for many aerobic gram negative bacterium including Pseudomonas & Aeromonas.
Since Pseudomonas & Aeromonas are common causes of opportunistic fin rot in fish (assuming the causes of this opportunity are negated), this drug or a combination that includes it may be a good alternative treatment.
In fact when combined with some Sulfa based medications, it produced a synergism or addition in 85% (similar to how Kanamycin and Nitrofurazone produce a synergism that treats Columnaris and Aeromonas that when treated alone, often results in failure).
However Trimethoprim has no proven effectiveness for anaerobic infections, so if the causes of an Aeromonas is anaerobic (which most are), then this or antibiotics containing Trimethoprim would be a poor choice.
USE: A good alternative to 100% sulfas, although a more harsh antibiotic toward nitrifying bacteria.
Especially useful for fin and tail rot.
*Can be very harsh to nitrifying bacteria in an aquarium, do not over dose and use only in well established aquariums.
*Can cause Thrombocytopenia (lowering of blood platelets), so this is a poor choice if fish have large wounds or are suffering from septicemia. A better choice then would be a pure Sulfa product or other medication combination.
Trimethoprim is found in:
*Mardel Maracyn Plus (contains Sulfamethazine and Trimethoprim)
NOT currently available
USE: Tetracycline is the name of a large class of antibiotics produced by Streptomyces bacteria.
These include Tetracycline Hydrochloride (to be discussed here) and several others which, although closely related, often yield very different results (although side effects may be very similar).
With this in mind it is important to not confuse these very similar but often very different in results antibiotics. Unfortunately this is done all too often, especially for the treatment of Columnaris (Flexibacter).
Minocyline which can be effective (not my first choice for Columnaris though) is often confused with Tetracycline Hydrochloride.
Tetracycline Hydrochloride is a naturally occurring Tetracycline used in the treatment of bacterial infections that are generally gram-positive such as Streptococcus and SOME gram-negative infections in fish.
It interferes with the production of proteins that the bacteria need to multiply and divide (bacteriostatic). However many bacterial pathogens have developed resistance to Tetracycline Hydrochloride.
Tetracycline Hydrochloride is generally more effective for aerobic bacteria (which Columnaris is only aerobic however Aeromonas and many other pathogens can be anaerobic).
It should also be noted as to Columnaris that although it is aerobic, it is also gram negative, whereas Tetracycline Hydrochloride is less effective for gram negative bacterium.
It is noteworthy that a member of the tetracycline family; Minocycline hydrochloride is more effective for gram negative bacteria than Tetracycline Hydrochloride.
Uses include (generally gram positive causes of these symptoms); fin and tail rot (split, ragged and deteriorating fin and/or tail), Popeye (protruding eyes, may be cloudy or hazy), gill disease (swollen, discolored gills, gasping for air and a decrease in activity) and secondary infections.
Tetracycline Hydrochloride mode of action is as a protein synthesis inhibitor via an aminoacyl-tRNA binding mechanism to the 30S subunit. Mode of resistance is the loss of cell wall permeability.
Note, Tetracycline can lower red blood cell count and cause anemia, because of this I would not use with injured fish, as this is the last thing you want to do with a bleeding fish.
Tetracycline becomes dangerous past its expiration date. While most prescription drugs lose potency SLOWLY after their expiration dates, tetracycline can become toxic over time.
This can be a useful antibiotic, especially when others fail, however Tetracycline is more useful in warm blooded animals (humans and Veterinary) than in fish.
I have often found the side effects to outweigh the benefits in aquarium use (such as anemia and interfering with nitrifying bacteria, often producing a “brown foam” on the surface of the aquarium), especially for marine aquariums.
For this reason (destruction of nitrifying bacteria) I strongly recommend against the combined use of Tetracycline AND Erythromycin (the side effects of these two antibiotics combined will generally negate any benefits obtained when used in combination).
Another note with Tetracycline Hydrochloride is that it is easily absorbed where calcium is present in larger quantities, which often renders this antibiotic useless in saltwater and high GH (hard water) freshwater aquariums.
DOSAGE: 250- 500 mg per 20 gallons of water. Every 48 hours (24 hours for severe issues) with a 25% water change before each treatment. This product will not work in water with a ph above 7.5- NOT FOR MARINE USE! (also not effective in freshwater aquariums with a pH above 7.6)
*Best not used concurrently with other antibiotics or chemical treatments, although use in a bath with Methylene Blue is OK.
*Do NOT use with fish suffering from ammonia/nitrite poisoning or with fish with low red blood cell count (anemia) such as suffering from an acute gill infestation of Velvet, Flukes or similar parasites that attacks the gills and thus renders a fish anemic
USE: Minocycline hydrochloride, also known as Minocycline, is a member of the broad spectrum tetracycline antibiotics, and has a broader spectrum than the other members, especially as to gram negative bacteria where Minocyline has more activity (albeit still limited effectiveness when compared to other gram negative antibiotics).
Minocycline is also synthetic whereas Tetracycline Hydrochloride and Oxytetracyline are naturally occurring. It should also be noted that Minocycline maintains serum levels 2-4 times that of most other tetracyclines (150 mg giving 16 times the activity levels compared to 250 mg of Tetracycline Hydrochloride at 24-48 hours).
It has excellent anti-inflammatory properties which makes it a good choice for septicemia, although for Viral Septicemia there is no effective treatment, only prevention.
Minocycline is also effective for fin/tail rot and OCCASIONALLY pop eye and is sometimes suggested for dropsy. However as for Dropsy I strongly recommend against this as this antibiotic can cause severe kidney damage, which is the last thing you want with a possible Dropsy case.
Minocycline is also skin absorbed like Kanamycin (although not as well) which can increase effectiveness. It is also nontoxic to invertebrates but should not be used in Marine aquaria.
Minocycline (like other Tetracyclines) is easily absorbed by calcium, making this a POOR choice for saltwater or high GH freshwater aquariums (such as African Cichlids, livebearers), in these cases Kanamycin is the better choice.
The above point is often missed by well meaning aquarists (often in many forums that love to recommend Maracyn-2).
The reason is that although Maracyn–Two (Minocycline) is a good product/medication when used in the right conditions for the right problem (of which it is relatively wide spectrum), the problem is that most aquariums I have either encountered or have been sent the water parameters for (emailed, etc.) have too high of a mineral level (GH over 200) for Minocycline to be truly effective.
In fact there in lies the problem in that often these same minerals that render Maracyn Two less effective, can IMPROVE the fish’ natural ability to fight disease (via better osmoregulation & Redox).
See more: Do Fish Drink, Osmorgulation
Another note about the dangers of Minocycline as with Tetracycline, is that Minocycline becomes dangerous past its expiration date, in other words expired Minocycline can become more toxic over time.
With these points in mind, generally the ONLY aquaria I recommend Minocycline in are Amazon River tanks such as Discus Aquariums.
DOSAGE: Maracyn-Two is the primary source for this anti-biotic, follow directions given by Mardel (manufacturer of Maracyn –2)
*Best not used concurrently with other antibiotics or chemical treatments, although use in a bath with Methylene Blue is OK
QUININE SUFATE (& Hydrochloride):
Quinine Sulfate causes pH elevation in intracellular organelles of parasites, this is thought to disrupt the intracellular transport of membrane components and macromolecules, and phospholipase activity leading to cellular failure of these parasites.
USE: Quinine Sulfate is useful for resistant strains of Ich (especially on scale less fish), as well as Protozoan caused sliminess of the skin and Rams disease (whirling disease).
Also useful for resistant strains of Hexamita when combined with Metronidazole.
DOSAGE : 250 mg per 10 gallons of water. Once a day for 4-5 days. Do a 25% water change before each treatment. Quinine Hydrochloride is generally more effective when available.
Oxytetracycline is a naturally occurring Tetracycline that is more broad spectrum than Tetracycline Hydrochloride (but not as broad spectrum as Minocycline, especially as to gram negative bacteria).
USE: Oxytetracycline will treat gram-positive and some gram-negative bacteria. Marine ulcer disease, cold water disease, bacterial hemorrhagic septicemia (Symptoms: Red streaks in body and fins), or redness in the body. Also open sores or loss of scales and mouth fungus.
DOSAGE: 250- 500 mg teaspoon per 20 gallons every 48 hours (24 hours for severe problems) with a 50% water change before each treatment. This antibiotic is best used mixed in with food, especially if your ph is above 8.0.
*Best not used concurrently with other antibiotics or chemical treatments, although use in a bath with Methylene Blue is OK.
*Do not use with fish suffering from ammonia/nitrite poisoning or with fish with low red blood cell count (anemia) such as suffering from an acute gill infestation of Velvet, Flukes or similar parasites that attacks the gills and thus renders a fish anemic
USE: Bactericidal for some gram-positive and many gram-negative bacteria causing disease in fresh water and marine fish.
Nitrofurazone inhibits several bacterial enzymes, especially those involved in the aerobic and anaerobic degradation of glucose and pyruvate.
This synthetic antibacterial is effective for control of Flexibacter/Columnaris such as these symptoms: Fuzzy, thin, white coating on the body and fins.
It is best combined with Kanamycin for effective treatment of Columnaris pathogens, in fact the COMBINATION of Nitrofurazone and Kanamycin is often the only effective treatment for Columnaris.
Nitrofurazone is also often effective for Aeromonas such as these symptoms: fish have blisters forming on the skin that are full of a clear to yellowish fluid, these blisters may turn into large sores.
As well Nitrofurazone is often effective for the related Vibrio and similar bacterial species.
Nitrofurazone is particularly useful for control of minor topical skin infections of freshwater & marine fishes that have not become systemic. As well, Nitrofurazone is effective for surface skin infections of Streptococcus iniae which may appear as a milky peeling slime.
Effective as well against marine ulcer disease and some protozoan infestations. For this reason, Nitrofurazone is a good next step treatment for wounds and other topical infections when first step treatments such as Pimafix or Melafix fail.
Nitrofurazone is also useful in treating Furunculosis often found in Koi.
Serious adverse events related to nitrofurans are very rare. Acquired resistance of bacteria to nitrofurans during therapy has been rare and has not appeared on a significant scale in over 50 years of use.
Do not use in the presence of invertebrates.
Nitrofurazone is more effective at lower pH levels, which means use for marine fish is best in baths, NOT the display aquarium!
Nitrofurazone is not Skin absorbed, so use of this Bactericidal for systemic infections is not recommended.
However Aquatronics and myself have found that Nitrofurazone combines well with Kanamycin (which is skin absorbing), and are very complimentary to each other! When Kanamycin and Nitrofurazone are combined these medications form a synergistic combination that is not totally understood, but what is known is that often leaving one or the other out of the equation or not using both at full strength often results in failure in treatments of stubborn/advanced bacterial infections such as Columnaris.
As well since Nitrofurazone is often better topically for Aeromonas while Kanamycin's skin absorbing properties combine well with Nitrofurazone for Columnaris.
Since these bacterial infections are often hard to differentiate by the average aquarist, this can be a good combination when unsure.
Further Reference: Nitrofural, Nitrofurazone; Skin Absorbing
*Do not use in the presence of live plants or many delicate invertebrates
*Not best used in saltwater display aquarium, better in hospital tank or bath with not carbonate decor
Aquatronics made excellent products (many that are simply no longer available in any form), but unfortunately went out of business in the early 2000s for business reasons which continue to haunt and perpetuate within the Aquarium & Pet industry in general, not for lack of excellent reliable aquatic treatments. In fact as a side note, purchasing aquarium products at companies such as Amazon, Pet Mountain and many others will likely result in more top notch aquarium information and supply companies disappearing as did Aquatronics, remember this the next time you attempt to save a $1 by purchasing at these types of retailers.
Nitrofurazone, Kanamycin, & Metronidazole were found in a few excellent products of theirs that are no longer available, but can be utilized by blending your own medications.
Here are two that can blended:
*Aquatronics Spectrogram: Nitrofurazone can be combined with Kanamycin to make an even more wide spectrum treatment, especially for difficult cases of Columnaris or Aeromonas.
For very serious combination bacterial/fungal/parasitic infections (such as Ichthyophonus or even virus infections such as “Angelfish aids”), especially in often difficult to treat Loach, Botia, Cory Catfish and similar fish; this combination PLUS SeaChem ParaGuard can often be the “kick” needed for a cure (assuming water conditions are also at proper parameters)
*Aquatronics Paragon 2;
Nitrofurazone OR Triple Sulfa can be combined with Kanamycin & SeaChem ParaGuard for a VERY strong fungal, & bacterial infection treatment.
Substitute Kanamycin with Metronidazole for an excellent parasitic, fungal, & bacterial infection treatment.
*Do not use as a medication for a fish food soak for internal treatment
USE: Neomycin (a Aminoglycoside) is a broad spectrum antibiotic that is effective for aerobic gram-positive, some gram-negative such as Aeromonas of the gut, and occasionally Mycobacterium tuberculosis (Mycobacterium marinum), which is neither Gram-positive nor Gram-negative due to high lipid content in its wall.
Effective for some Gram-negative bacteria- Open red sores or ulcerations, intestinal infections, fin and tail damage.
In severe cases where fins and tail are eaten away- treat with Kanamycin for this.
As well, Neomycin can be PART of a treatment for mycobacterium tuberculosis (symptoms, weight loss, a distended abdomen, loss of appetite, fin erosion, unusual coloration, spinal deformities, and listless behavior).
Neomycin is ineffective against fungi, yeast and viruses.
Neomycin is not absorbed by the intestinal tract and is effective in treatment of diseases thereof. But Neomycin can damage the kidneys as it is nephrotoxic when it enters the bloodstream, however since this drug is not readily absorbed in the intestinal tract it is useful for treatment of pathogens such as Aeromonas, particularly of the gut, that can lead to Dropsy or similar diseases.
Neomycin works well in freshwater or saltwater aquariums.
Neomycin is very effective when used in feeding due to the fact that this antibiotic does not get absorbed. This is my preferred way to treat with this antibiotic.
For external use, Neomycin is more limited in use and should be used as you would the Human product; Neosporin.
That use would be for minor cuts, injuries, etc., not for major bacterial infections, especially since most major external fish infections are gram negative infections that Neomycin is not effective for. External use would be also similar to recommended use of Melafix.
DOSAGE: To prepare medicated fish food with flake, FD, or frozen fish food; Use One Measure (2-5 gallon "in tank" dose) of Neoplex per 15 minute fish food soaking for an average 60 gallon bio load aquarium (I use "just enough" water to mix fish food and Neomycin).
After soak, pour entire contents into aquarium.
For in tank treatment; 250 mg per 10 gallons of water.
Treat every 24 hours with a 25% water change before each treatment. Treat for 10 days. For tuberculosis, use for up to 30 days (Can be and should be combined with other treatments such as Isoniazid for Fish TB).
*Do not use with fish suffering from inflammatory or ulcerative gastrointestinal disease
USE: Metronidazoles primary use is for the treatment of anaerobic gram positive bacteria including those that produce beta-lactamase. However, it is not effective against aerobic bacterium.
As well Metronidazole is effective for some protozoa (especially internal flagellates).
Due to Metronidazole effectiveness against anaerobic bacteria (by selectively blocking some of the cell functions of anaerobic bacteria) this drug along with Neomycin is a good choice for bloating of the digestive tract (common in goldfish).
Metronidazole selectively blocks some of the cell functions in anaerobic bacteria, resulting in their demise.
Metronidazole is also a good choice for many protozoan parasite infections, especially for Cryptocaryon in marine aquaria.
Metronidazole is also effective used in combination or by itself for internal parasites such as Nematodes or Trematodes. In marine aquarium infections is where Metronidazole really shines as it is very effective internally and since Marine fish are always drinking the water around them, medication is easily transported to the infected area. In Freshwater, treatment can be improved by soaking food as well and this is still an effective freshwater treatment as well.
Common aquatic uses for Metronidazole; Hole in the head disease (hexamita), chilodonella, plistophora (parasite disease usually seen in neons and cardinals that causes loss of color, darting, and eventually death.
(Please read “Neon Tetra Disease” in the reference section), salt water ich, bloat.
Metronidazole can be combined with Nitrofurazone and Methylene Blue (1/2 dose for the Methylene blue) for an alternative treatment for anchor worms, especially for Trichlorfon sensitive fish.
Metronidazole is unique in some of its effectiveness and is excellent to combine with other treatments especially when affecting a cure is difficult (such as many internal parasites).
Probably the Aquarium Industries top fish remedy manufacturer, Aquatronics (that unfortunately went out of business), used Metronidazole in many of its multi antibiotic remedies as it very useful in combination.
DOSAGE: 250-500 mg per 20 gallons. Treat every 48 hours (24 hours for severe problems) with a 25% water change before each treatment. Treat for 10 days.
To prepare medicated fish food with flake, FD, or frozen fish food;
Use One Measure (2-5 gallon "in tank" dose) of Metronidazole per 15 minute fish food soaking for an average 60 gallon bio load aquarium (I use "just enough" water to mix fish food and Neomycin).
After soak, pour entire contents into aquarium.
Metronidazole is often used in treating early stages or for prevention of Neon Tetra & FNT Disease.
Reference: Neon Tetra & FNT Disease
ABOUT/ USE: An easily absorbed antibiotic, it is used to treat many sensitive gram–negative and some gram–positive bacteria.
Kanamycin is a water-soluble aminoglycoside antibiotic that is derived from the bacterium Streptomyces kanamyceticus and has a very low adsorption rate in the intestine of animals including fish.
Aminoglycosides work by binding to the bacterial 30S ribosomal subunit, causing misreading of t-RNA, leaving the bacterium unable to synthesize proteins vital to its growth. Aminoglycosides such as Kanamycin are useful in infections involving aerobic gram-negative bacteria such as Columnaris (especially when combined with Nitrofurazone).
Kanamycin works especially well in salt water aquariums.
As noted a few times earlier in this article, Kanamycin works well combined with (& compliments) Nitrofurazone for flexibacter (Columnaris), which may includes these symptoms; fuzzy, thin, white "saddles" on the body and fins.
Also useful for Pseudomonas-Open red sores or ulcerations, fin and tail damage, fins and tail are eaten away, in severe cases, down to the body.
Kanamycin is very effective in high pH applications, especially Vibrio, making it useful for brackish and marine treatments. Kanamycin is easily absorbed skin absorbed, making it an excellent choice for systemic infections.
Kanamycin is one of the more effective broad spectrum antibiotics available with recent tests showing it to surpass the Tetracycline class antibiotics in cultures including Minocyline (found in Maracyn II), although Kanacyn has been also been shown in these studies to be even more effective when combined with other antibiotics such as Nitrofurazone or Tetracyclines for a “super” antibiotic effect.
Kanamycin can also be used for aquatic Tuberculosis (Mycobacterium marinum), although Isoniazid is often the drug of choice, both can be used together as Isoniazid seems to affect certain active TB bacterium whereas Kanamycin has often different TB activity effectiveness (Kanamycin can also be combined with Neomycin for difficult cases of Mycobacterium marinum.
I personally have found this to be one of the more effective antibiotics available (similar properties to Chloramphenicol, although still not as effective as Chloramphenicol which is no longer available in the aquarium trade).
Kanamyacin can be effective for whirling disease, suspected kidney disease and dropsy. Kanamycin tends to be absorbed quickly by the kidneys which makes it effective for treatment of Kidney infection, but also lends itself to the destruction of the kidneys with over use.
Kanamycin sulfate appears to prevent bacteria from making their cell walls, so the cells die.
As noted earlier, Kanamycin can be blended with other medications to make a few popular Aquatronics Medications/Treatments that are no longer available.
Here are two that can blended:
*Aquatronics Spectrogram: Kanamycin can be combined with Furan 2 to make an even more wide spectrum treatment, especially for difficult cases of Columnaris or Aeromonas.
*Aquatronics Paragon 2; Kanamycin can be combined with Furan 2 & Metronidazole for an excellent parasitic, fungal, & bacterial infection treatment.
DOSAGE: 500-750 mg per 20 gallons. Treat every 48 hours (24 hours for severe problems) with a 25% water change before each treatment. Treat 3 times or up to 10 days in severe cases (with water changes immediately before each treatment).
*While often one of the few aids to treating early onset Dropsy, care should be exercised since Kanamycin will also damage or destroy Kidneys if over used or if the kidneys are already severely compromised
Further Reference: Dropsy in Fish
Chloramphenicol has in vitro activity against most anaerobic bacteria (gram positive/negative), and aerobic gram-positive bacteria making this one of the more effective antibiotics I have ever used for fish due to its wide spectrum effectiveness, especially as per many aquatic bacterial pathogens (and even some parasites too).
Unfortunately the toxicity of Chloramphenicol, which has been linked to the development of aplastic anemia (a rare but potentially fatal condition) and dose-dependent leukopenia, has made this antibiotic impossible to find for most aquarists due to strict regulation, with Kanamycin Sulfate the closest substitute (although still not as useful in my experience)
ABOUT/ USE: Fin and tail rot, infections attributed to kidney disease (often not true kidney infections), some causes of pop eye, False Neon Tetra Disease/FTD, and certain causes of "Black Molly disease".
Erythromycin is most effective for gram-positive (the drug of choice for Streptococcus & Eye Infections in fish) and SOME gram negative bacteria and fungus appearing diseases, not what is generally considered true fungus).
In fact there is sadly much misinformation about the use of Erythromycin for "True Fungus" which is 100% incorrect as one Betta Forum diagnostics incorrectly recommended Erythromycin for Fungus which any check of most medical literature will show NO recommendations for such treatment. The use of Erythromycin for a true fungal infection or similar appearing Columnaris will waste precious time and likely result in the death of your fish.
Erythromycin is considered primarily a gram positive treatment and should be used accordingly
Generally Erythromycin is not effective for most common aquatic diseases, especially in saltwater aquariums since it is primarily gram positive while the majority of aquatic infections are gram negative.
This is not to say Erythromycin is a useless treatment for aquarium use, as it is still useful for some diseases especially some of the more difficult gram positive infections such as Streptococcus, some cases fin rot and even some causes of Neon Tetra Disease (not all as this is more a symptom of several possible causes rather than an actual disease).
Another often effective use of Erythromycin is for eye infections, both pop eye and cloudy eyes (cataract like infections), however in both cases a medicated Methylene Blue/Salt bath should also be part of the treatment (if possible, as some large fish this is not possible).
Direct application of Silver Nitrate or Potassium Permanganate may be necessary for severe cloudy eyes (cataract like eye infections).
When used for many eye infections (especially when only one or a small percentage of fish are effected), use of Erythromycin at double dose in a medicated fish bath is often an effective and definitely safe method of use.
Further Reference: Medicated Fish Baths, How to perform
I find that Erythromycin (often in the trade named product Maracyn) is one of the most improperly recommended aquatic medications available (based on feedback from clients and reading forums, especially Yahoo Answers).
Although I have used this antibiotic with success, it is rarely a medication that I will go to first other than for specific diseases/conditions since it is limited in its aquatic effectiveness and is hard on nitrifying bacteria.
This is a medication worth trying when all else has failed or even in combination with antibiotics such as Kanamycin, but as a first choice Erythromycin should be very limited other than the before mentioned infections (such as Streptococcus & serious gram positive eye infections).
Erythromycin works by inhibiting protein synthesis by binding to the 23S rRNA molecule (in the 50S sub-unit) of the bacterial ribosome blocking the exit of the growing peptide chain of sensitive microorganisms.
Animals including fish do not have 50 S ribosomal subunits, but have ribosomes composed of 40 S and 60 S subunits.
Certain resistant microorganisms with mutational changes in components of this sub-unit of the ribosome fail to bind the drug. The association between erythromycin and the ribosome is reversible and takes place only when the 50 S sub-unit is free from tRNA molecules bearing nascent peptide chains.
Gram-positive bacteria accumulate about 100 times more erythromycin than do gram-negative microorganisms. The non ionized from of the drug is considerably more permeable to cells, and this probably explains the increased antimicrobial activity that is observed in alkaline pH, which is why Erythromycin is more effective in pH over 7.2
PLEASE NOTE!! Erythromycin is also VERY harsh on nitrifying bacteria, especially above 7.2 pH and should be used with care in aquariums, although in established aquariums the nitrifying bacteria will generally bounce back.
When used with faculative bacterial support products such as SeaChem Stability, this lowers the risk of dangerous ammonia spike issues.
Having a "pre-seeded" (with aerobic nitrifying bacteria) sponge filter or other filter media in another healthy tank to move over to the Erythromycin treated aquarium is very helpful in quickly re-establishing/repairing your aquarium nitrogen cycle.
Use of a bare hospital tank with a seeded sponge filter is another idea when practical (not for aquarium wide infections). Product Resource: SeaChem Stability
I would not recommend Erythromycin in new aquariums or Marine Aquariums due to activity that can harm bio filters.
Generally Erythromycin is best not combined with other medications, although I have combined with Kanamycin under careful observation of aquarium ammonia levels.
DOSAGE: 250- 500 mg per 20 gallons every 24 hours with a 25% water change before each treatment. Treat for 10 days.
*Do not use in new aquariums (under 8 weeks) where the nitrifying bacterial colonies are likely not well established
*Do not mix with other primarily gram positive medications such as any Tetracycline
*Do not use if fish have Dropsy
ISONIAZID 300 mg:
ABOUT/USE: Treatment for tuberculosis.
Symptoms include: the fish have been sick for several months, the fish is lethargic, anorexic, has fin or scale loss and a sunken stomach.
Isoniazid Can be combined with Kanamycin or Neomycin.
As noted, Isoniazid is used alone or can be used with other drugs to treat tuberculosis (TB) and to prevent it in fish that have had contact with tuberculosis bacteria.
It eliminates ONLY ACTIVE (growing) bacteria.
Since the bacteria may exist in a resting (nongrowing) state for long periods, therapy with isoniazid (and other antituberculosis drugs) MUST be continued for a long time (usually 6-12 months) often making TB treatments in aquariums impractical due to costs, time, and damage to the aquatic environment (I strongly recommend using a quarantine tank).
Unfortunately, Isoniazid has become very difficult to obtain since the premier aquarium medications company, "Aquatronics" went out of business due to the declining business climate in the aquarium industry. Neomycin is an alternative for Mycobacterium tuberculosis, as well Kanamycin is considered a second line drug for Mycobacterium tuberculosis (not a first line since many strains of Mycobacterium tuberculosis are resistant to Kanamycin)
An organic alternative is Usnea, which has shown very good lab results in treating the Mycobacterium tuberculosis.
For more about Usnea, please see this Aquarium Answers article: USNEA; USING USNIC ACID AS A FISH REMEDY
Note: Aquatic tuberculosis can be very difficult to treat (in fact nearly impossible).
Also note that this is caused by a very similar bacterium in human TB, but is not the same, and the only danger to humans is to an open wound exposed to the bacterium, which then only causes a localized rash.
DOSAGE: 1 tablet per 20 gallons, every other day for 14- 30 days
PENICILLIN & AMPICILLIN;
USE: Belonging to the group of beta-lactam antibiotics, ampicillin is able to penetrate Gram-positive and some Gram-negative bacteria.
Even though this a commonly used antibiotic family in humans and other warm blooded animals, this is a family of antibiotics that has shown to be GENERALLY USELESS in fish (especially Penicillin).
About the only effectiveness comes in the treatment of some fungal-like eye infections.
All medications, antimicrobials, antibiotics, chemotherapeutics work differently in differently in different organisms, even if the processes are similar. An example I often use is for Quinine Sulfate; this is a generally safe and effective treatment for fish, but not at all for invertebrates.
The same goes for both Penicillin and Ampicillin, while these are often useful for humans, their use for fish is VERY LIMITED AT BEST, and should basically never be used in an aquarium.
NALIDIXIC ACID (Naladin):
Nalidixic Acid is a quinolone, a family of broad-spectrum antibiotics.
Nalidixic Acid (also known as Naladixic Acid and Naladin) is effective against many gram negative and positive bacteria.
In humans it was, as the antibiotic is no longer used for humans, used for urinary tract infections.
Naladixic Acid is similar in its effectiveness to Septra (AKA Trimethoprin).
In aquariums it has been shown to be occasionally effective for swelling caused by fluids in the internal cavity of the fish that is often diagnosed as Dropsy.
It has also shown effectiveness in treating sporozoans (Pleistophora hyphessobryconis) sometimes referred to as neon tetra disease.
For this application Naladixic Acid works best combined with Metronidazole or Gentian Violet. Although for this condition I prefer a Methylene Blue bath and Metronidazole in the aquarium (or possibly Quick Cure or ParaGuard).
Caution should be used with Nalidixic Acid in hard water aquariums as high amounts of calcium will interact with this antibiotic.
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