Thursday, December 1, 2011

Caution in Mixing Antibiotics

Most of this information is taken verbatim from  I added some additional comments to aid in determining which antibiotics are in which class.

Antibiotics for Beef Cattle
By Heather Smith Thomas

Subcutaneous Injections
Originally, SubQ injections were used because a particular product was highly irritating to muscle tissue or designed for slower rate of absorption. Today, however, due to concerns about carcass quality (trying to avoid IM shots, where possible) more injectables—including some antibiotics as well as vaccines—are being approved for subcutaneous use and no longer must be given IM. When you have a choice, according to label directions, it’s best to inject the product under the skin rather than into muscle, for less tissue damage. IM shots are more likely to develop a serious abscess if a needle is dirty. An infection introduced by a SubQ shot is merely beneath the skin and an abscess more readily breaks open to drain.
For a SubQ injection, lift a fold of skin on the neck or shoulder where skin is loosest, and slip the needle in between the skin and muscle. If using a trigger-type syringe, aim it alongside the animal so the needle goes under the skin and not into the muscle. For a small calf, it may be easiest to give a SubQ injection under the loose skin of the shoulder, and if there’s any local reaction it won’t make his neck sore (and hinder his desire to nurse).

Giving injections SubQ rather than IM allows you to use a shorter needle (¾ inch if using a trigger type syringe, or up to 1 inch if using both hands to tent the skin and slip the needle underneath) so it’s less likely to bend or break. In the confined space of some chutes, insert the needle at an angle so you can use a one-handed technique with a syringe gun, rather than both hands to tent the skin. There’s less risk of getting your hands injured (jammed between the animal and the chute) or accidentally hitting yourself with the needle, if you can do it one handed.

Intravenous Injections
Some medications are more effective (acting faster and more readily absorbed) if given IV. Some are very irritating to muscle tissue and must be given IV. It’s not difficult to give IV injections, but they must be done properly. Chances for problems are greater, as is the speed with which a serious problem may develop, so you must know which products can be given IV (follow label directions) and know what you are doing. Large volumes of fluid or medications given too swiftly can put too much load on the heart, and some drugs speed up the heart. Heart rate should be monitored when giving fluids or certain IV medications, and rate of administration adjusted accordingly.

Any large vein will work for an IV injection, including the large veins under the tail, the big milk vein ahead of the udder on a lactating cow, or the jugular vein on either side of the neck (located in the groove above windpipe and esophagus). A large needle (at least 16 gauge and 2 inches long or longer) works best for adult animals.

For IV injections, needles and any other equipment (syringe or tubing) must be sterile. The animal must be well restrained so it can’t move around during the procedure. If using the jugular vein, find it and press down on it with your fingers or fist to build up pressure (between your hand and the animal’s head) so the vein stands up and is easier to inject. Still pressing on the vein, insert the needle into it at a point between your hand and the animal’s head, then move the needle a little forward (inside the vein) parallel with the neck. If blood flows freely from the needle, this shows it’s in the vein and you can then attach your syringe (or tubing, if giving fluid).

The most common problem is pushing the needle too far, clear through the vein and out the other side. Sometimes the animal moves and the needle slips out of the vein. Don’t just assume it’s in the vein just because you see some blood. Blood will flow rapidly and steadily from the needle if it’s actually in the vein. Make sure the needle stays in the vein when you give the injection or administer the fluid. Injecting some products into tissues around the vein can cause severe irritation and stress (and sometimes death, depending on the drug). If the needle slips out of the vein while giving fluid the tissues around the vein will start to swell. If the needle slips out of the vein, take it out and start over. If giving fluid, which means the needle must be in the vein awhile, it’s best to use an IV catheter, which is longer than a needle and more flexible, and stays in the vein better.

Always use a sharp, sterile needle. Use of disposable needles ensures the needle will be clean and sharp, but avoid those with plastic hubs because they are more likely to break. Use proper diameter for the job; too large and it allows leakage, too small and it may break or slow the procedure and more pressure is needed to inject the material through it (never try to put a thick product through a small needle). If it’s too long it may bend or break. Too short and it may not deliver the product into proper location.

Needles should not be reused unless they’ve been boiled between uses. Exceptions are when a large number of cattle are being vaccinated at once. In this instance, care must be taken to make sure the needle stays clean and sharp during multiple uses. Injections should never be put into dirty hide (covered with mud or manure). Make sure the area to be injected is clean and dry. Thrusting a needle through wet or dirty skin will take contamination with it, creating risk for an abscess at the injection site. It’s always better to vaccinate cattle when they are dry, rather than wet from rain or snow. Even if you are using the same needle multiple times on several animals, always use a clean sterile needle for refilling your syringe; never insert a used or dirty needle into the bottle or you may contaminate the contents.
If a needle gets dull or dirty after being used on several animals, exchange it for a new one. Needles are designed to cut into the skin, not puncture it. After you’ve used a needle on 10 or more animals, it starts to dull and develop a burr on the tip. Once it’s dull, you need more force to put it through the skin, producing more tissue damage. Instead of cutting through the skin, a dull needle punctures it and folds a small piece of skin under, possibly carrying dirt or bacteria with it. If a needle starts to get dull or gets a blunt tip from being bumped on the chute, discard it for a new one, even if you’ve only used it on one animal.

Always discard a needle if it becomes bent. Bending weakens it and it may break. You don’t want it to break off in the animal. Make sure the needle is still attached to the syringe when you finish the injection. On the rare occasion one breaks off in an animal, it may be sticking out and you can grab it. Otherwise, mark the site so your vet can surgically retrieve it—and do it as soon as possible. A needle shaft can migrate several inches within an hour, working deeper into the muscle or traveling laterally under the skin. When working cattle, have a container by the chute for disposal of used needles.

Some of the gun-type syringes have flexible ends to minimize the risk for bent or broken needles. If you use a trigger type syringe, make sure it’s easy to use and well lubricated for quick ease of motion, especially if you have small hands. The easier and faster you can give an injection, especially if the animal has any room to move around, the less likely you’ll end up with bent or broken needles. Make sure you have good access to the injection site and your hand or syringe/needle won’t be jammed into the bars or front of the chute if the animal lunges forward or backward. Many of the new squeeze chutes have access doors at the neck area or a neck extension that holds the head and neck still while you are trying to give an injection.

A Local Veterinarian’s Perspective
Certain illnesses and disease conditions in cattle are caused by bacteria, and stockmen generally treat these with antibiotics. Some types of antibiotics kill bacteria and others inhibit their growth. Use of the proper antibiotic can help the sick animal fight the infection. 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 work with your veterinarian for proper diagnosis and treatment.

Jeff Hoffman, DVM, raises cattle and has a veterinary practice near Salmon, Idaho, a ranching area where his clients are mainly cow-calf producers. Choice of an antibiotic when an animal is ill should always be a case by case situation; there are no hard and fast rules for what works best. “We basically use antibiotics in beef animals for 3 purposes—prophylaxis (preventative medicine), metaphylaxis (a combination of treatment and prevention, as when a group of stressed calves arrive at a feedlot after a long transport, and all of them are mass treated upon arrival), and therapeutic—actual treatment of an illness. So you need to have a plan about what you are doing,” he says.

“Most over the counter drugs (penicillin, tetracyclines and some of the sulfas) list 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, so you must be working with your veterinarian anyway, on diagnosis and treatment. This is the whole idea behind prescription drugs. An adequate label (to cover everything it might be used for, or stipulations regarding proper use) can’t be written,” he explains. In order to use a prescription drug there also has to be a valid doctor/client/patient relationship. The veterinarian must diagnose and prescribe, before he/she will put a drug into the client’s hands to treat the animal. Otherwise, these drugs are not legal for stockmen to use.

“The 2 main classes of antibiotics are bacteriocidal (that kill pathogens) and bacteriostatic (that inhibit their growth). Bacteriodical products include penicillin, the cephalosporins, aminoglycocides, peptides, and trimethoprim. Bacteriostatics include the tetracyclines, chloramphenicol (which cannot be used in food animals), the macrolides, sulfonamides and tylosin,” says Hoffman. Drugs from these 2 classes generally should not be used at the same time. Some products can be used effectively together, such as two bacteriostatic products (like tetracycline and long-acting sulfa boluses, for treating pneumonia or foot rot), because they are synergistic and work better together.
·         Bacteriocidal class antibiotics (spelling can also be bactericidal)
o   Penicillin
o   Cephalosporins (Naxcel, Excenel, Excede)
o   Aminoglycocides
o   Peptides
o   Tremethoprim
o   Another class of antibiotics is the fluoroquinolones, which includes Baytril (enrofloxacin) and A180 (danafloxacin) which are generally considered bactericidal
·         Bacteriostatics
o   tetracyclines
o   chloramphenicol (which cannot be used in food animals)
o   macrolides (Draxxin, Micotil, Erythromycin)
o   sulfonamides
o   tylosin
o    Phenicol class drugs (Nuflor)  it is generally bacteriostatic but can be bacteriocidal at higher doses

“But if you mix a cidal and a static, they tend to cancel each other out. If the 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 have to know what you are doing, or follow your veterinarians advice on which drugs to use.

Another factor to be aware of whenever you use antibiotic products is residues and observing proper withdrawal time before the treated animal is sold or butchered. Different products have different withdrawal times, and the time frame is also contingent upon dose. If you overdose the animal, withdrawal time would be longer than stated on the label. It is illegal to sell an animal before an adequate withdrawal time has elapsed, and any carcass containing drug residues will be condemned.

“In our region, cow calf operations are fairly isolated and not having a lot of cattle coming in from other regions. For the most part I rarely use antibiotics, and when I do I generally stick with the cheaper traditional over-the-counter products. They work just as well as the newer, more expensive products,” says Hoffman. There hasn’t been as much problem yet with resistant strains of bacteria, and the older products still work. It’s not like a feedlot, with cattle intermingling from several sources.

“If antibiotics haven’t been abused on a ranch and there are no resistance issues, the older products work fine. In most cases, depending on the situation, pneumonia can be adequately treated with LA-200 and sulfa, and this is what I’ll use for the first line of attack. If I have a herd-wide outbreak where I know the cattle are stressed and I know they have other problems going on, I have at times gone through and treated everything with Micotil, to head it off. But usually on an individual case by case basis I don’t jump for the big guns,” he explains. And in the majority of cases, he knows the herd health and knows the cattle have been vaccinated, covering all the viral diseases.

First of all, when dealing with any disease condition, you need to figure out whether you are dealing with bacteria or a virus, and if the herd health management is good, and you know that a viral outbreak is less likely. The herd husbandry makes a big difference in the health of the animals. If stress levels are kept low and there’s a good herd health program, there’s much less need for use of antibiotics.

“Except in rare situations, I almost never use antibiotic in scouring calves anymore,” says Hoffman. Supportive care, like giving adequate fluids and electrolytes, is more important. In some cases he will use antibiotics, depending on the situation, but years ago a person automatically gave scouring calves pills and a shot. He stopped doing that some years back because it didn’t make that much difference.

The animal has to fight off the infection; the immune system of that individual animal is what determines whether it can recover or not. Antibiotics merely help buy time for the animal to mount its own defenses. The state of the animal will also be part of the determining factor regarding which antibiotic you choose. “In a really stressed, immunocompromised animal, you’d want a bacteriocidal antiobiotic that will kill the bacteria, because the body isn’t as able to fight them off,” says Hoffman.

“Antibiotics by themselves are never going to cure the problem. You are just helping tip the scales in the right direction. This is why people with AIDS die. If the body doesn’t have a viable immune system, no matter what you do, that animal will die. Antibiotics by themselves won’t cure the disease.” This is why it’s important to have good health conditions, with proper nutrition (including adequate trace minerals) and a healthy immune system, and a good vaccination program to stimulate immunity.

Good supportive care can also help tip the scale in the animal’s favor. “Banamine is helpful in a case of pneumonia (and approved for this use), because it decreases the incidence of lung lesions. It also reduces fever and inflammation and makes the animal feel better,” he explains. If they get back on feed and will eat and drink and get their strength back up, they can fight off the disease quicker.

Regarding which antibiotic to use in a specific case, he says the only way you absolutely know is to grow a culture and do a sensitivity test. “Then you know exactly what that bug is and can test it with different antibiotics to see which one works best. You also have to know whether it’s a drug that will get to the target organ (such as the lungs, or wherever the infection is located),” he says. Every situation is not ideal for figuring this out, however.
Usually you don’t have time to grow a culture before you start treatment (the animal may be dead before you get the results), so the veterinarian chooses something he/she thinks might work in the meantime. A culture can help guide your decision in the future if you might have multiple cases in that herd, however. “You need to have enough knowledge to know that what you are growing in the culture is the cause of the infection, and not just a secondary bacterium that just happens to be there, too,” says Hoffman.

Thoughts From a University Professor
Dr. Geoffrey Smith, North Carolina State University, says there are several good antibiotics effective against pneumonia-causing bacteria. “This is a huge market for drug companies and there aren’t any control trials done by independent researchers to show that a certain drug works the best. All we have is drug company data. There are 5 or 6 products that I consider good. Some work better in some situations, and others work better in other cases. The ones I use a lot are Micotil and Nuflor, but you should not use Nuflor in calves less than 30 days of age because it tends to make them scour. It’s hard on the GI tract,” says Smith.

“Baytril is fairly good and some people use it for pneumonia in calves. Another good one is A180 (Danafloxacin). It’s about the same as Baytril but it concentrates in the lung a little better. In our region it’s been about half the price of Baytril, so I use more of it than Baytril. Slaughter withdrawal time is only 4 days for A180, which is a lot shorter than some of the other drugs,” he says.

“Draxxin is the newest product and the good thing about this drug is how it concentrates in lung tissue and stays there for about 8 to 10 days. The down side is cost,” he says. The big market for it is in feedlots; they have a lot of respiratory disease and use a lot of antibiotics and have more total dollars at stake with each animal lost. Feedlots use it in large quantities and can get a better price break than veterinarians can get, says Smith. But eventually it may become more affordable for the cow-calf producer.

“With any drug, we need to monitor how the calf is doing and if it’s not getting better within a few days we need to give something different,” he says.

Cost Sampling at a Local Clinic
Costs of drugs will vary from region to region and from time to time. Here is what the most commonly used antibiotics are at the Blue Cross Veterinary Clinic in Salmon, Idaho, and the cost to the client on a certain day in January, 2008 (costs can vary with each new order, however):

LA-200 500 ml. $53.00
Baytril 100 ml. 95.00
Nuflor 100 ml. 64.00
Draxxin 100 ml. 350.00
Tribrissen tablets (100) 21.00
Abscesses & Scar Tissue
An abscess will usually show up as a lump, a few days after the injection. It may grow larger then break and drain. If it doesn’t break on its own it should be lanced and drained and flushed. An even greater problem, however, is an abscess deep in the muscle, since it may not be detected until the animal is slaughtered. Scar tissue from a surface abscess can result in significant carcass trim, but a deep abscess may contaminate the meat around it and it must be trimmed even more drastically.

Even a poke into muscle with a clean needle without injecting anything leaves a small scar and a tough area in the meat. Sterile scar tissue in the muscle after a shot can still be there months or years later. Injections given to a calf may create lesions that must be trimmed at slaughter 2 years later or even a dozen years later when a cull cow goes to market. These sites contain more connective tissue and fat than normal muscle, and the meat may be less tender in an area up to 3 inches around the lesion—a piece of meat the size of a grapefruit.

When you give any kind of injection, always keep in mind the possibility of an adverse reaction. These problems are most common if a product is given in overdose or inappropriate location. For instance, a product might be safe when administered SubQ but fatal if injected into a blood vessel. A few animals are sensitive to certain products and will react even if the injection is given properly. The reaction may be as mild as local swelling at the injection site that subsides in a few days, or may be serious and life threatening if the animal goes into shock.

Temporary swelling is usually nothing to worry about, but if you inject the neck too close to the shoulder, swelling makes it hard for the animal to walk. That shoulder can’t be moved forward without discomfort. Some types of vaccine are notorious for causing local swelling, and some animals react more than others. To avoid making the animal lame, put a neck injection well ahead of the shoulder, closer to the head.

A more serious type of reaction occurs when an animal is very sensitive to the product being injected, producing a severe allergic response (anaphylaxis). This may result in constriction of air passages and difficult breathing. The animal may go into shock, collapse, and die. Signs of severe hypersensitivity reaction may develop within 10 to 20 minutes or longer. Usually the more severe the reaction, the sooner it occurs.

When using any injectable product, keep an emergency antidote on hand, and know the proper dosage to give. You may never need it, but if you do, swift injection of epinephrine (adrenalin) and dexamethasone (a steroid—safe for a non-pregnant animal) will usually reverse the condition and enable the animal to recover. Always observe cattle after vaccinating (or any other injection) and check them for at least 2 hours for any signs of shock. If a certain animal ever shows a serious reaction to a particular product, do NOT give it again to that animal. A second exposure usually produces an even greater reaction in the already sensitized animal, and it may die.

Using any animal health product in a way not specified on the label (at higher or lower dose, more frequent intervals, in different location or route of administration, or in a different species than intended) is illegal without a veterinarian’s prescription. Even if it’s not harmful to the animal, there may be more risk for residues. A drug intended for another species (such as a non-food animal) may leave residues in meat since withdrawal times have not been determined. Detectable residue at slaughter is a violation that results in condemnation of the carcass.

There are situations, however, when a vet will prescribe a product in an off-label use for certain purposes or to treat an unusual condition. This is acceptable, according to the FDA, only if there is no approved drug already labeled to treat that condition or if treatment at recommended dosage or location would not be effective. There must be a valid veterinarian/client/patient relationship for this to be legal, which means the vet has a good working relationship with the client and has seen and diagnosed the animal and agrees to take responsibility for making a judgment regarding health and treatment—and the client agrees to follow the vet’s instructions. A record of any off-label treatment must be kept, and withdrawal time before marketing for slaughter must be extended in the case of some products or overdoses, with the time determined by the veterinarian.

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