Which One?
By Heather Smith Thomas
Certain types of illnesses and infections are caused by bacteria. Stockmen generally treat these conditions with antibiotics. Some types of antibiotics kill bacteria and others inhibit their growth. Use of the proper antibiotic can help the animal fight off the infection. There are many different kinds of antibiotics available today and sometimes it’s hard to know which one to use.
The important thing is knowing when an antibiotic would be helpful (or not) and which drugs might work best for certain conditions. This is why it is crucial to read labels, and to work with your veterinarian for proper diagnosis and for recommendations regarding the most effective treatment.
Most bacterial infections are amenable to treatment with antibiotics. Most viral diseases are not affected by these drugs. The only reason your veterinarian might prescribe an antibiotic in these instances would be to prevent or control any secondary bacterial infection that might develop. In many cases the initial viral infection weakens the animal’s resistance and allows opportunistic bacteria to invade and multiply, and the bacterial infection may be more deadly than the initial viral infection.
Different Kinds of Antibiotics
The antibiotic drugs in use today include several types and classes. Some of the newer ones are macrolides (a group of antibiotics produced by certain species of Streptomyces, a genus of fungus-like bacteria). Many of the commonly used products today are prescription drugs, as opposed to older over-the-counter sulfas, penicillins and tetracyclines. These newer drugs include Draxxin, Nuflor, Excede, Baytril, Micotil, Tetradure 300, and Naxcel. Some stockmen also continue to use LA-200 and other over-the counter forms of tetracycline, and various brands of penicillin and sulfa. A few use tylosin or erythromycin.
Jeff Hoffman, DVM (a veterinarian who raises cattle near Salmon, Idaho) says the choice of antibiotic should always be on a case-by-case basis. “We basically use antibiotics in beef animals for 3 purposes—prophylaxis (prevention of disease), metaphylaxis (a combination of treatment and prevention—as when a group of stressed calves arrive at a feedlot after a long transport), and therapeutic (actual treatment of an illness). So you need a plan,” says Hoffman.
“Most of the older over-the-counter drugs (penicillin, tetracyclines and some of the sulfas) say on the label what they can be used for, so you need enough knowledge to know what you are treating. All the newer drugs require a prescription to obtain them, so you need to be working with your vet on diagnosis and treatment when using those. This is the whole idea behind prescription drugs. A label that would cover everything a drug might be used for, or stipulations regarding proper use, would be impossible to write,” he explains. There must be proper diagnosis to begin with, and a valid doctor/client/patient relationship before the veterinarian will put that drug into the client’s hands to treat the animal. Otherwise, these drugs are not legal for stockmen to use.
Hoffman explains there are 2 main types of antibacterial drugs— bacteriocidal ones that kill pathogens, and bacteriostatic drugs that simply inhibit their growth. “Bactericidal products include penicillins, cephalosporins, aminoglycocides, and trimethoprim. The bacteriostatics include the tetracyclines, chloramphenicol (which cannot be used in food animals), the macrolides, sulfonamides and tylosin,” he says. Drugs from these 2 classes should not be mixed together or used at the same time. Some products can be used effectively together, such as two bacteriostatic products like tetracycline and long-acting sulfa for treating pneumonia or foot rot, because they are synergistic and work better together.
“But if you mix a ‘cidal and a ‘static they tend to cancel each other out,” says Hoffman. “If bacteria are growing very slowly or not at all, due to use of a bacteriostatic drug, the bacteriocidal drug won’t work to kill them,” he explains. Thus you need to know what you are doing, or follow your veterinarian’s advice on which drugs to use.
A Closer Look at the Newer Options - Draxxin (tulathromycin, which is one of the macrolides) is a long-acting drug that’s very useful for combating respiratory disease. It is labeled for use both as therapy and as a control (to prevent disease). “We can legally administer this product to cattle that we as veterinarians believe are at risk of developing disease,” explains Kelly Lechtenberg, DVM, PhD (consulting veterinarian at Midwest Veterinary Services in Oakland, Nebraska). For instance, it can be given to stressed animals after a long transport, upon arrival at their destination.
“Draxxin carries a bovine respiratory disease label and could be used at weaning if calves are stressed. The duration of effectiveness is at least 10 days. With Draxxin you rarely need to re-dose. If the animal has not responded adequately in that length of time and you feel it needs additional treatment, I feel it’s probably better to switch drugs and go to a different class of antibiotics,” he says.
“In the same drug class (macrolides) we also have Micotil (tilmicosin). It’s been around longer, is also a long-duration therapy product (at least 3 or 4 days) and has a slightly different spectrum than Draxxin, but they are generally used for treating the same types of condition. One caution with Micotil is human safety considerations,” he says. Micotil can be fatal to humans if accidentally injected.
Both Draxxin and Micotil are prescription products. The producer must be working with a veterinarian for proper diagnosis and treatment, so a veterinarian will be giving the drug or instructing the client in its proper use. This is especially important for the cow-calf operation, where the stockman may be putting a syringe in a saddlebag or taking the drug to treat a calf—wherever he can get hands on the animal—without ideal restraint conditions. A feedlot operator, by contrast, will be putting the animal in a treatment facility where there’s less risk for struggle and accidental injection of a human. “If I were to poke myself accidentally with a drug of the macrolide class, I would rather poke myself with Draxxin,” says Lechtenberg. “It has no human health implications.”
Another macrolide is erythromycin, but it’s very irritating to muscle tissue. “The only label way it can be used is intramuscular. In my opinion there is no place for injectable erythromycin in modern therapy,” says Lechtenberg.
Another drug approved for use in respiratory disease is Nuflor (florfenicol), which is in a different class of drugs—the same class as chloramphenicol, which is no longer allowed for use in food animals. This class of drugs is very effective and broad spectrum. Nuflor often works well for treating respiratory infections, but some veterinarians do not use it in calves less than 30 days old because it tends to make them scour.
Nuflor’s effective duration of activity is at least 4 days. “The main question stockmen ask, for any of these drugs, is how many days should they watch the animal (for response/improvement) before they switch drugs. I’d give Draxxin at least a week (up to 10 days), Micotil 3 days and Nuflor 4 days,” explains Lechtenberg. If the calf is slipping backward—not making progress in recovery, you need to re-evaluate the diagnosis. Is this just respiratory disease or does the calf have other issues?
“It may be a primary viral infection, and the antibiotic may keep bacterial load down (to prevent severe secondary infection) but the real problem is viremia. In that instance, changing antibiotics won’t do much good. Or, you may have a chronic condition in the lung (especially in feedlot cattle) and the antibiotic isn’t effective,” he says. In a cow-calf operation this is generally not the problem, since the stockman is usually dealing with a calf that’s sick for the first time. In that instance, you generally expect the response to be good.
The cephalosporins are another class of drugs, introduced about 20 years ago. These include Naxcel, Excenel and Excede. “Naxcel is very short acting (about 1 day) but a wonderful product in respect to residues. There’s either zero or very short withdrawal time with these drugs. They are in the same general class with penicillin, but much more potent and broad spectrum than the base compound of penicillin. They are good for respiratory disease and foot rot. Treating foot rot is one of the big uses for cephalosporins because this keeps your slaughter options open for adult cows,” he says. If an older animal gets foot rot and you want to try therapy, but realize that you might have to butcher or sell the animal, you won’t have to wait so long on withdrawal time if you use one of the cephalosporins.
“The products labeled for foot rot include LA-200, Nuflor and several others but many of these have significant withdrawal time. If they don’t get the job done you have to hang onto the animal longer than you want to. The cephalosporins are a better choice in that situation,” explains Lechtenberg.
The cephalosporins all consist of the same chemical entity—ceftiofur. “These drugs include Naxcel, Exenel, (effective duration about 2 days) and the newest one Excede. It’s a different formulation, in a different carrier, so it has a longer duration of effectiveness. The mechanism by which that happens is different than in Draxxin or Micotil which are absorbed rapidly and then concentrate in the white cells of the body. Excede is absorbed more slowly, so it’s like giving a continuous slow-release dose. It is effective for about 10 days, very similar to Draxxin, and is also a good drug to give cattle upon arrival at a feedlot,” he says.
Naxcel would be the drug of choice when treating an adult cow (if it’s an animal you could put in the chute again for retreatment if necessary, and to take advantage of the short withdrawal time if you decide to sell or butcher her afterward), whereas Excede might be better when receiving calves into a feedlot—where you want to process them and not have to handle them again.
“When deciding whether to use Draxxin or Excede as your long-action drug—one thing to consider is that Draxxin is helpful in operations that have problems with Micoplasma bovis. Some farms and herds have had a serious problem with this. Draxxin (a bacteriostatic macrolide) is effective against this pathogen. Excede has a similar duration of efficacy, but because it is a cephalosporin (a class of bacteriocidal drugs that work by inhibiting the formation of bacterial cell walls) it doesn’t work at all for M. bovis because micoplasmas do not have a cell wall,” explains Lechtenberg.
Thus your choice of antibiotic would depend on the history of disease on your ranch. If you struggled last year at weaning time with Micoplasma bovis, and decide to dose the calves at weaning this year to head it off, you’d want to use Nuflor, Draxxin, LA-200 or one of the other drugs that have efficacy against this type of bacterium.
Another class of antibiotics is the floroquinalones, which includes Baytril (enrofloxacin) and A180 (danafloxacin). “These two drugs are different variations, and both are very effective and potent. The parent compound is ciprofloxacin, a human antimicrobial.” The latter is a broad spectrum antibiotic effective against some strains of bacteria that have developed resistance to penicillins and cephalosporins.
“Baytril and A180 have some restrictions. They carry warnings on the label, saying it is illegal to use them in any extra-label fashion, such as for baby calf diarrhea. These drugs are very effective against E. coli and salmonella, but the reason they are illegal for this use is because there’s concern about development of antibiotic-resistant gut bugs (enteric pathogens) that can infect people. These drugs can be used for baby calf pneumonia (they are labeled for treating pneumonia in beef cattle) but not for scours,” he points out.
All the newer drugs require a prescription from your veterinarian. You should not be using them without advise from and consultation with your vet. The only drugs you can legally purchase over the counter without a prescription (from a feed store, catalog supply company, etc.) are penicillin, sulfa and the tetracyclines.
The Old Reliables
Most ranchers are familiar with drugs that have been in use a long time, like sulfa boluses, LA-200, penicillin, and injectable tylosin. “These drugs still do what they did in earlier years, but the new ones do more,” says Lechtenberg. On many farms, however, the combination of LA-200 and sulfa still work to combat respiratory disease, because the targeted bacteria have not yet developed resistance.
Dr. Mark Hilton, Clinical Associate Professor, Beef Production Medicine, Purdue University, says producers need to know what works best for treating common problems on their own farm. “For pinkeye or foot rot, long-acting tetracycline is probably the first thing most veterinarians would tell you to use. It’s cheap, effective, and gives several days’ coverage,” he says. You don’t need a prescription for this one, and it’s nice to have something on hand in case an animal needs treatment on a weekend or a time when it’s not convenient to make a trip to town or to have your veterinarian come out.
“Many farms or ranches have not had the pressure experienced by large feeding operations that are always bringing in new cattle, with higher exposure to antibiotic resistance development,” says Lechtenberg. “Feedlots have a lot more pathogens than the home farm. The feedlot animal has more stressors, and these are cattle we’re putting a lot of antibiotics into, even though we all know that the body’s immune system is what ultimately determines whether the calf responds to therapy or not. All we are trying to do is give the animals another crutch to help fight disease, even though they will succeed or fail on their own ability to fight off the infection,” says Lechtenberg.
Some of the older, less expensive products still have a place. If they still work on your ranch, there’s no reason to not use them. If they don’t work very well, then you can switch to the newer, more expensive drugs. “The rule of thumb in the feedlot world is that we hope for an 85 to 90% success rate (response to therapy, in the animals treated). In the cow calf world, however, this is not good enough, but to expect 100% response rate is unrealistic. In the cow-calf environment, regarding respiratory disease, if you are getting 95% success in response to therapy, this is great, and you don’t need to change antibiotics. We expect some cattle to fail, and the first time you have a calf that needs re-treated doesn’t mean you had antibiotic failure. If cattle are responding to an inexpensive program, with low relapse rate, there’s no need to change just because there’s a newer antibiotic available,” he says.
One of the newer formulations of oxytetracycline is Tetradure 300. “This injectable oxytetracycline contains 300 milligrams per milliliter, compared to Biomycin 200, LA-200, generic equivalents, etc. It’s not longer-lasting but is more potent, so you can give a smaller volume dose (less risk for tissue irritation and reaction). It’s the same amount of drug in less volume. Potency has to do with the characteristics of the antibiotic. The most potent products are those like Draxxin, in which you can treat a very large animal with just 10 cc’s,” explains Lechtenberg.
The drug companies have focused not only on the spectrum of activity (the types of bacteria the drug will kill) but also putting the drug into carriers that don’t make excessive volume. “We want low volume products because they are less likely to cause injection site reactions (and are more efficient to store, ship and administer) and less likely to be painful to the cattle. We also want a high margin of safety for the cattle, in case we happen to overdose them,” he says.
Tylan (tylosin) is still available. “When given intramuscularly it is very irritating to tissues. IV usage is extra-label but there’s good data on its effectiveness against pneumonia. The most common use of that drug, however, is in feed to prevent liver abscesses, and it is sometimes used in a salt/mineral product for pinkeye control. There’s also a powder form, for pinkeye treatment in baby calves,” says Lechtenberg.
Sulfa is still used, as boluses for baby calf diarrhea, and boluses for pneumonia and foot rot. There are also some combination therapies such as long-acting sulfa boluses given in conjunction with LA-200 to give 3 days’ worth of coverage.
There are many choices for selecting a product that fits a specific need. “When I graduated from veterinary school we only had the penicillins, sulfas and tetracyclines. This is why many products were used extra-label. We’d get together and talk about how we could mix this or that, to address a particular problem. But compounding is not acceptable anymore because there are so many good products available,” explains Lechtenberg.
Penicillin is still used, but it generally needs to be given in higher than label dosage to be effective. Even though you can purchase it over the counter, in order to use it extra-label you need to have a prescription from your veterinarian. Almost everyone who uses penicillin gives it several times the labeled dosage, since this is the only way it’s effective for certain conditions.
“It was labeled using a septicemia model. This class of drug is absorbed quickly from the tissue into the bloodstream. A calf with pneumonia needs it in the lung tissue, not the blood. When drug companies were doing efficacy tests, the tests were modeled on blood borne infections (septicemia). So they came up with very low doses; it doesn’t take very much penicillin to treat septicemia. But for foot rot, pneumonia, pinkeye, and other conditions, we have to drive the blood concentration very high so we can get spill-over effects into the tissue. Then it works well,” he says.
“Penicillin is safe. It’s not toxic, so there’s no problem with giving high doses. But since this is extra-label, someone must be responsible for residues.” Thus you need to work with your veterinarian for proper withdrawal time for the higher dosage.
“One problem with penicillin is that it’s one of the most common allergenic antibiotics. Some people are allergic to penicillin and its derivatives, since it is often used in human medicine,” he says. Since it is usually administered in the muscle, if you give a calf 5 times the label dosage and only observe the normal label withdrawal time, there will be residue in the muscle if that calf is butchered too soon.
“If the neck muscle is ground into hamburger and contains residue, somebody who eats that meat may go into anaphylactic shock. So this is a caution when using penicillin, even though it can do a good job on foot rot and some cases of calf pneumonia. But in order to get tissue levels high enough, you have to use so much that it’s almost cheaper to use one of the newer drugs. For clostridial infections, however, penicillin would be the drug of choice. At label dose, penicillin would be very effective against clostridia (blackleg, malignant edema, redwater, tetanus, etc.,” says Lechtenberg. Thus you need to work with your veterinarian to diagnose and treat various conditions, to know which antibiotics and dosages would be most appropriate.
USE ANTIBIOTICS PROPERLY
If an antibiotic is needed, select the one most appropriate for the condition you are treating. Some people use the “shotgun” approach and give 2 or 3 different drugs at the same time. “If the researchers who produced these drugs thought that putting 2 or 3 of them together was better, they would have already done it,” says Hilton.
He often hears farmers say that such-and-such antibiotic doesn’t work. “It probably works, but they were either too late starting treatment, or didn’t have the right diagnosis, or used an inadequate dose (underestimating the weight of the animal) or the nutrition or environment of the calf was compromised after treatment,” says Hilton.
THINK BEFORE YOU INJECT
“If you inject an animal that really didn’t need the antibiotic, and then decide you want to sell or butcher that animal, you’ve got a problem,” says Hilton. “Just doing something because you want to try to help the animal isn’t always the right thing. The old saying—‘don’t just stand there, do something’ should be: ‘don’t just do something, stand there, and think,” he says.
As an example, he had a client (about 20 years ago) with a 7-year-old cow that got her leg caught in a bale feeder and broke her leg. “He knew it was broken, and called me on a Saturday evening and asked if it could wait until Monday to be looked at. I said absolutely not; it needs to be splinted. I asked him to tell me about the cow. He said she had a calf that spring that got scours and died, and she wasn’t a very good cow, so I said, ‘Why don’t you just butcher her?”
But the rancher had given her a shot of long-acting penicillin. “I asked him why he did that, and he said he wanted to do something for the cow. But now we were faced with a 30-day withdrawal before the cow could be butchered,” says Hilton.
“So I went out there and he had a trip charge, and an emergency fee to splint her leg. Then a few days later she got out in the pasture, got down in a little draw, couldn’t get up, bloated and died. All of this could have been avoided, but the producer gave antibiotics before he thought about it.”
RESIDUE ISSUES
When using antibiotics, check labels for withdrawal time; it is important to allow proper length of time before the treated animal is sold or butchered. Different products have different withdrawal times, and the time is also dependent upon dose. If you overdose the animal, the withdrawal time must be longer than stated on the label. It is illegal to sell an animal before an adequate withdrawal time has elapsed. Any carcass containing drug residues will be condemned.
COSTS
Some of the newer drugs are more expensive than the older ones. Categorically, the newer generation products will cost 2 to 3 times more than the older products, partly because less volume or fewer doses are needed. Actual costs will vary from one supplier or veterinary practice to another. Draxxin is probably the most expensive, regarding per head cost for therapy, based on a certain size/weight animal. In descending order of cost: Draxxin, Excede, Nuflor, Baytril, and Micotil. Then costs drop to a lower price range with tetracyclines, then the sulfas and penicillins.
When deciding what to use, consult with your veterinarian, and also discuss what you need to keep on hand. “You don’t need an arsenal of medication,” says Hilton. “One or two antibiotics would be plenty for most cow-calf operations. Sometimes I go to a farm and find that the owner has a bottle of something that cost him $100 and it’s outdated—and he’s hardly used any of it. It’s better to just have what you might need. Long-acting tetracycline and penicillin are both relatively inexpensive and can be kept on hand because they are useful for a number of infectious diseases,” says Hilton.
DRUG TYPES AND CLASSES:
SULFONAMIDES – (Bacteriostatic) these include sulfadimethoxine and sulfamethazine and the drugs used in beef cattle include Albon (effective against coccidiosis protozoa) and Calf-span boluses.
PENICILLINS – (Bacteriocidal) these include Procaine penicillin G and benzathine penicillin (long acting Dual Pen), amoxicillin, etc. and a few IV formulations (potassium penicillin and sodium penicillin) that are very expensive.
CEPHALOSPORINS – (Bacteriocidal) related to the penicillins in structure and mode of action. These drugs include ceftiofur (Naxcel, Excenel, Excede)
TETRACYCLINES – (Bacteriostatic) biosynthetic antibiotics; some isolated from certain species of Streptomyces and others produced semi-synthetically from chlortetracycline or oxytetracycline. Broad spectrum, effective against gram negative and gram positive bacteria, rickettsia, mycoplasmas, chlamydia and certain viruses and protozoa. These drugs include LA-200, Biomycin, Duramycin, Tetradure 300, etc.
TRIMETHOPRIM – (bacteriocidal) antibacterial product closely related to pyrimethamine (an anti-milarial drug). Given orally in combination with a sulfonamide because the two together are much more effective than either one alone.
MACROLIDES – (bacteriostatic) several types include tulathromycin (Draxxin), tilmicosin (Micotil), tylosin (Tylan) and erythromycin.
PHENICOLS – (a unique class of drugs that has both bacteriostatic and bacteriocidal properties)Nuflor is the drug in this class that is approved for use in food animals. Chloramphenicol is a related drug, but illegal for use in food animals.
FLUOROQUINOLONES – (bacteriocidal)These include enrofloxacin (Baytril) and danafloxacin (A-180)
AMINOGLYCOCIDES – (bactierocidal) - These include gentimycin, spectinomycin and neomycin. These can’t be used in injectable form in food animals, but can be used orally, since they stay in the gut and are not absorbed into the rest of the body.
