Clostridial Myositis - Following Injections and Precautions for Banamine Injections

Many horsemen give injections to their horses. These include vaccinations, antibiotics, and sometimes other medications. Most injections are given intramuscularly, but there are a few medications that should always be given intravenously. 

Intramuscular injections occasionally cause local abscesses if the needle or skin is dirty when the injection is given. Sometimes, abscesses occur even with very clean conditions. The worst kind of injection-induced infection is called clostridial myositis, or myonecrosis. 

This type of infection is caused by certain types of clostridial bacteria that are present in the environment. Some of these bacteria live in the horse’s intestines and don’t cause problems under normal conditions. They are present in manure and form spores that last a long time in the environment. They are often on the horse’s skin and can be taken into the tissues with an injection. These bacteria can be in a dormant state, and then multiply when conditions are right, growing best in an airless environment without oxygen, such as bruised and damaged tissue with very little blood supply.

The dormant spores “come to life” when they have favorable conditions in which to multiply and start producing deadly toxins. Different clostridia cause different diseases. Examples include: tetanus, malignant edema, blackleg in cattle, enterotoxemia in young calves and foals, or life-threatening gut infection and diarrhea in young foals. 

Some types of intramuscular injections seem more risky for clostridial infections, especially flunixin meglumine (Banamine and its generic equivalents), if given in the muscle rather than in the vein. One theory is that this drug sets up an ideal pH in the tissues for these bacteria to grow (basic, as opposed to acidic). A clostridial infection can happen with any kind of injection, but Banamine has been the most common.

Dr. Ray Randall, a semi-retired veterinarian in Bridger, Montana, says to be aware of the possibility of adverse reaction any time you give an injection. “This can occur with vaccinations, injections of vitamin E and selenium, etc. But Banamine is the one we are most aware of (since it seems to be most often associated with reactions), and it doesn’t matter how well you give the injection; there is always a risk. Clostridial bacteria may already be in the horse’s body in spore form, just waiting for something to set up the right environment (such as damaged tissue from the injection),” he says.

Irritation from the drug can cause part of that muscle to die. Normally this is not a big deal, but it can set up an anaerobic environment which enables clostridia to thrive. It’s not the bacteria themselves that cause the problem; it’s the toxin that they secrete. When they multiply, they produce toxins that damage the surrounding tissue even more and produce gas. You can feel air bubbles under the skin – crinkly like bubble wrap. 

“I have some slides taken many years ago of a horse I treated in 1989 for a clostridial infection following vaccination. He survived, but was disfigured from the infection and was just used as a lesson horse after that,” says Randall. 

“With Banamine or any of the generic flunixin products, the only way to minimize the risk is to give it orally or IV, and never in the muscle. It does have an intramuscular label on the bottle [stating that it can be given either IV or IM] though there is also a warning about possible adverse reactions when given IM, which include clostridial infection.” This drug is safest to give orally, but works fastest if given IV.

“When people are giving injections of any kind, the number one thing is to be clean. Don’t inject into a dirty area on the neck or buttocks. We used to use alcohol, but it really doesn’t do much good (it’s not a very good disinfectant),” he says. If you use alcohol, let the area dry again before injecting; a needle going through wet skin and hair is more likely to take dirt/bacteria with it.

“Use a sterile needle, a new syringe and choose a clean spot on the horse. That’s about all you can do to try to prevent problems. If you notice swelling later or if the horse is not doing as well you’d expect, get veterinary help – the sooner the better. Load that horse in a trailer and take him to the vet, rather than calling and waiting for the vet to come to you,” says Randall.

“The horse I treated for clostridial myositis in 1989 received a vaccination. He was not very good about injections, and the owner gave it to him in the hindquarter (but not in the best location). This horse also had a history of reactions,” he says. 

“It was a Friday when the owner called. The horse had received the vaccination early in the week. He always got stiff and sore after vaccination, and the owner had been doing some massage and chiropractic work on this horse. When they called me, it didn’t sound good. When I walked into the barn, I could smell that horse – a sickly sweet odor put off by clostridial organisms. The horse was standing out in the arena, holding his left hind leg up. The whole leg was cold and swollen, with gas bubbles under the skin all the way up the leg,” recalls Randall.

“I got him started on antibiotics, clipped his hind leg from hock to croup, and figured out where the major problem areas were. We cleaned those up and made a lot of incisions to open them up, let the gas out, and start drainage. The tissues were dead and rotting. We didn’t have to use any anesthesia to make the incisions because he had no feeling at all in those tissues. These were incisions 8 to 12 inches long,” he says.

“We asked about euthanasia. The horse was insured for a fair amount of money and I told the owner the chances of surviving this infection were poor and it would be reasonable to euthanize him, but we’d have to call the insurance company first. The owner told me to save the horse if I could. So, we got the horse loaded and took him to our clinic. He was already starting to feel better, just from the antibiotics and opening up those areas; you could tell by the way he acted,” says Randall.

“We kept him in the clinic about a month and he ended up sluffing an area in his left thigh, leaving a hole as large as half a watermelon where all the muscle was gone. His sciatic nerve kept functioning, however, and his hip joint was okay, so he survived and was able to keep going.” Randall recalls.

Some horses aren’t this lucky. Randall tells of another horse that had an infection at an injection site-on top of the gluteal muscles (rump area). “There was noticeable swelling. I gave the horse antibiotics, loaded him in a trailer and took him to the clinic and he was dead when I got there,” Randall says.

The first ivermectin deworming products for horses were injectable and there were several incidents of clostridial infections with those. “Here at our clinic, we probably used about 3,000 doses of it during the time it was available as an injection, and it was my favorite dewormer. We always gave the horse an injection of penicillin in the same region, at the same time.” This eliminated the risk because penicillin is very effective against clostridia.

“We never had any trouble with those injections, but the company later went to an oral product partly because of injection reactions, but mainly as a marketing tool because it was easier for horse owners to give it orally,” says Randall.

Proper Ways To Use Banamine

 “It is less risky to give this orally or by IV injection rather than as an IM injection,” says Randall. “There are times you need it when a horse is flopping around on the ground with colic. If you plan to have any flunixin products on hand, however (whether paste or injectable), you need to be able to assess that horse and know whether you should actually give this drug. That means you need to be able to take a pulse, listen to gut sounds, and look at the gums to know if the horse is shocky,” he says.

“An owner called one night wanting me to come to the fairgrounds and give fluids to a horse. This was about 11 p.m. The show vet had looked at the horse earlier and said it needed fluids. The owner had given the horse an injection of Banamine about 7 p.m. and it wasn’t doing well. I asked about the history on the horse. The owner said it wasn’t eating well that morning, so they gave it Banamine. This means the horse was sick all night by the time they discovered it was off feed that morning, and probably sick the day before. They didn’t want to haul the horse to a vet because they had to show some other horses the next day. They just kept giving it more Banamine, and a day or two later, after the show, they hauled the horse home and it died. The owner just assumed they could keep giving it Banamine!” says Randall.

When Banamine first came out about 1980, people considered it a cure-all. “We thought we could just give a shot of Banamine and make the horse better. But, we soon found out that the horses that needed surgery didn’t get surgery as soon as they should. We’d give Banamine, and it would be 4-5 hours before the horses started showing they were sick again. Sometimes, those few hours were the difference in whether they lived or died. If the horse is not a surgical candidate, giving Banamine is fine. But if the horse does need surgery, you shouldn’t wait. There is a lot of responsibility that goes with the owner giving Banamine – whether the paste or the injectable (whether by IV or oral).”  

Banamine may mask colic symptoms enough that you end up being a little late with the decision to do surgery. The horse seems better after the Banamine, so the owner goes off and does something else for a while, and then comes back to find the horse is worse again. By then, it may be evening, and the optimum window of time for doing colic surgery (before the horse is too shocky and the gut too compromised) may be gone.

“If the horse is shocky and you give a full dose of Banamine, this is hard on the kidneys because that horse is dehydrated (not as much circulating blood volume, because of shock). Or if you have a hard-working horse that’s dehydrated, you need to get 10 to 15 liters of fluid into him before you give him any drugs. And then you should give only a quarter or a third of a dose of Banamine,” he explains.

Dr. Matt Randall, a veterinarian at Collier Equine, in Waller, Texas, says there seems to be more risk for clostridial infections with full doses of Banamine, compared to a half dose or less. “You can give the product orally, however, to reduce risk for problems. I recommend to my clients that if they can’t get the injectable product into the vein, to just give a little extra and squirt it in the mouth. It tastes terrible, but they can get it into the horse that way if the horse is having a serious problem like colic,” says Matt.

Many people have given IM injections of Banamine for years without problems, but they need to be aware of the risk. “It’s a low risk, but it is a risk. I have seen three cases and all of these horses were very sick and toxic. There is often a fair amount of swelling at the injection site. The typical ‘calling card’ of clostridial myositis is gas bubbles under the skin. It feels like Rice Krispies. If you ever feel gas under the skin on a horse that’s recently had an intramuscular injection, this is serious and warrants an emergency visit to the veterinarian. It can make a big difference in the outcome if you can start treating it early, to reduce the extent of complications.”

The most recent case he’s seen was when a horse owner called to say her horse colicked a couple days earlier. “She had some Banamine, but couldn’t give an injection in the vein so she gave it in the muscle. The next day, her horse was a little stiff-necked and sore at the injection site, so she gave some penicillin, which was fine. Two days after the Banamine shot was when she called me. The mare’s neck was swollen on both sides and she had a fever of 104, and a toxic line on the mucous membranes on her gum.

“The owner told me what had happened, so I was looking for evidence of gas under the skin – because I was thinking it probably was a clostridial myositis. I didn’t find any gas near the injection site, but finally found a pocket of gas under the skin by her withers. The gas had travelled up and along the neck, clear to the withers. I prepped the skin at the injection area and blocked it with anesthesia as best I could and made incisions through the skin and partway down into the muscle with a big scalpel,” he says.

One of the important aspects of treatment is to open up the area and get oxygen down into the infection. Those bacteria don’t like oxygen. They thrive in damaged tissue with no oxygen supply.

He made several deep incisions and dissected down into the muscle. “Then suddenly my finger fell into an opening and I thought maybe I’d been unlucky enough to drive my finger into a large blood vessel. I was afraid it might start bleeding, but realized I had to pull my finger out. When I pulled my finger out of the wound, gas rushed out of that hole and the stench was foul. So, I opened it up even more, grabbed chunks of necrotic muscle tissue and dragged it out. I opened the infected area as best I could, then packed it with penicillin-soaked gauze and started the mare on penicillin injections. Another drug that is very effective against clostridia bacteria is metronidazole,” he explains. A horse with this kind of infection would also need a tetanus booster.

“With this mare, I got lucky. She survived, but with large scars on the side of her neck and some atrophy in those muscles, but all in all she did pretty well. The most important thing in dealing with this type of infection is getting oxygen into the affected tissues, and that’s why you see photos of horses with large, gaping incisions into those areas – for oxygen and drainage,” he says.

“If a person has access to a hyperbaric oxygen chamber, that would be ideal, but most people are not close enough to one, and/or can’t afford those treatments. This type of oxygen therapy is an excellent treatment modality for clostridial myositis.”

If the injection site and subsequent incisions are on the neck, the horse will have a very sore neck for a while and it might be painful to put his head down to eat and drink. “You need to help these horses by placing feed and water a little higher for easier reach. If the horse is in decent body condition to begin with, even if he can’t eat very well, it will take several days before he starts dropping muscle condition and body weight. But supportive care to help him eat and drink can keep him from losing too much weight. Depending on where the injection was that caused the infection (neck or hindquarters), you may or may not be able to give IV fluids,” he says.

“With this particular mare, with infection in the neck, venous access was not an option because of all the infection and gas under the skin. Trying to get into a vein with a catheter would risk a more serious problem. You can clean the surface of the skin, but you can’t clean out the contaminated subcutaneous tissue. A person can always give fluids and nutrients via stomach tube (nasogastric tube), which would be safer in this situation than an IV. There are some tubes that are designed to be left in place for several days, and the horse could be fed that way,” says Randall.

The mortality rate with this type of infection is fairly high, so it’s important to
get your veterinarian involved as soon as possible, to increase the chances of turning
it around quicker.  

Banamine Administration Options

“To avoid risk for this kind of infection, flunixin products like Banamine should never be injected into the muscle,” says Tia Nelson, DVM (Helena, Montana). “They can be given intravenously or orally. There is a Banamine paste, and I encourage people to use it if they want Banamine on hand in case their horse colics. In an emergency, the injectable form of Banamine can be given off-label orally (squirted into the mouth),” she says.

“Flunixin is readily absorbed from the GI tract and works about as fast as when given IM, but IV administration gives fastest response (which is usually what you want in a horse with colic). Flunixin is somewhat irritating to mucosal tissues; you shouldn’t give it very often orally or it may cause ulcers (partly because it’s irritating and partly due to the basic pH). But if you need to get Banamine on board and don’t know how to give it IV, you could squirt the injectable drug into the horse’s mouth – rather than risk an IM injection. It’s not labeled for oral administration; however, it’s labeled for IV only.”  

The liquid form is absorbed readily through mucosal tissues of the mouth and probably is effective even quicker than the oral paste. “IV injection, by someone who knows how to do it, is the best route, but don’t try it unless you know what you are doing because if any of this solution leaks out of the vein, you have another big problem. If horse owners need to keep some on hand, and have a prescription for it, and are giving it at home, they need to be confident in their ability at giving an IV injection. For most of my clients, the paste is safer and simpler to have on hand, without potential for this reaction.

If some of the drug slips out of the vein into the surrounding tissue, it burns and damages that tissue, creating serious swelling and blocking the vein. “This may wreck the vein (ending up with jugular vein thrombosis), but that’s not a life-threatening thing, compared to a clostridial infection that may kill your horse. Any time you can avoid a problem, it’s better than trying to fix it afterward,” Nelson says. The old saying, “an ounce of prevention is worth a pound of cure,” is very true in this instance.