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Pros And Cons Of Antibiotic Injections In Equine Joints

Because of the finesse with which equine veterinarians inject medications into joints, the procedure can appear uncomplicated. While injecting joints with antibiotics can help clear infections, the procedure is not without risks. Veterinarians must therefore consider a number of important factors before moving forward with intra-articular antibiotic therapies.

Managing Osteoarthritis

Medicating joints with corticosteroids, polysulfated glycosaminoglycans, or hyaluronic acid is commonplace in equine sports medicine. Intra-articular injection is often used in conjunction with other modalities, including oral joint health supplements. Oral products decrease inflammation and improve mobility, boosting the overall health of joints. Examples of appropriate products include high-quality supplements that contain proprietary combinations of glucosamine hydrochloride, chondroitin sulfate, MSM, and hyaluronic acid.

According to a recent review of intra-articular antibiotic use, 78 percent of veterinarians use intra-articular antibiotics in combination with other medications.^* By adding an antibiotic, often amikacin, to corticosteroid or polysulfated glycosaminoglycan, veterinarians hope to sidestep the development of a septic joint.

Considering the low risk of infection following joint injections, the question then becomes whether or not veterinarians should use prophylactic antibiotics. Moreover, because intra-articular antibiotics are used “off-label,” no researched guidelines for appropriate intra-articular use exist.

Prophylactic intra-articular antibiotic use therefore has two major ramifications:

Veterinarians may administer an excessively high dose. “According to some evidence, antibiotics like amikacin have toxic effects on cartilage cells and other joint tissues,” said Peter Huntington, B.V.Sc., M.A.C.V.Sc., director of nutrition at Kentucky Equine Research.
Unnecessary use of antibiotics contributes to antibiotic resistance. “With few new antibiotics in development and growing multidrug resistance to currently available medication, revisiting the practice of prophylactic antibiotic use in horses may be warranted,” Huntington added.

These concerns associated with intra-articular antibiotic administration supports alternative strategies for maintaining joint health.

Managing Septic Joints

Intra-articular antibiotics are indispensable in the face of a septic joint because direct administration into the joint can achieve high local drug concentrations. If, on the other hand, antibiotics are offered orally, high dosages would be needed for longer durations to achieve the same result as an intra-articular injection.

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“Systemic antibiotics, however, may be associated with important and potentially life-threatening side effects such as gastrointestinal disturbances that disrupt the microbiome. In the face of microbiome disarray, pathogenic bacteria may proliferate, altering immunity and increasing the risk of diarrhea or laminitis,” Huntington explained. When systemic antibiotics must be administered, gastrointestinal support in the form of research-proven supplements should be considered.

Local antibiotic delivery directly into a joint may also:

Improve owner compliance as injections do not rely on the owner administering the entire course of oral antibiotics;
Make treatment more affordable, as a systemic antibiotic maybe be cost prohibitive for an owner;
Shorten the course of treatment and improve outcomes; and
Result in high concentrations at the site of infection that may be particularly useful for fighting “floating biofilm,” which is an accumulation of microbes embedded within a self-produced extracellular matrix that helps protect the bacteria from antibiotics.

^*Pezzanite, L.M., D.A. Hendrickson, S. Dow, L. Chow, D. Krause, and L. Goodrich. 2021. Intra-articular administration of antibiotics in horses: Justifications, risks, reconsideration of use and outcomes. Equine Veterinary Journal:13502.

Joint Care: Provide Support After Wounds, Infection

Viscous and transparent, synovial fluid acts as a biological lubricant within musculoskeletal mechanisms. Penetrating wounds to joints and tendon sheaths cause most infections, though pathogens carried in the bloodstream, as with foals diagnosed with joint ill, have been implicated, as has contamination at the time of intraarticular injection or surgery. Veterinarians refer to infection that sets up in any structure containing synovial fluid, namely joints, tendons, and bursas, as synovial sepsis.

Prompt diagnosis and aggressive treatment minimize damage to septic structures and often prevent career- and life-threatening consequences. To determine if infection is present, bacterial isolation through culture is the best diagnostic tool, yet low sensitivity and long laboratory turnaround time often preclude a definite diagnosis in the face of emergency situations and treatment decisions, which may include joint irrigation and surgery. Because of these limitations, researchers have sought alternative ways to quickly identify the presence of infection.

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Austrian researchers recently evaluated the presence of specific biomarkers, called antimicrobial proteins, in synovial fluid as a way to confirm infection.^* These proteins are activated by the immune system in response to a pathogenic challenge, so their existence in the fluid indicates sepsis. According to the researchers, “using enzyme activity as a biomarker of synovial sepsis enables the development of a point-of-care diagnostic test, which would allow veterinarians to perform, analyze, and act on test results stall-side, in a matter of minutes.”

In the study, researchers collected synovial fluid samples from three groups of horses: healthy controls, horses with aseptic synovitis (inflammation without infection), and horses with septic synovitis. Enzyme activity assays were compared with standard synovial fluid parameters and broad-range bacterial DNA extraction.

The researchers found enzyme activities were significantly different between septic synovial samples and aseptic and control samples, leading them to believe that measurement of enzyme activities would allow for reliable, rapid diagnosis of synovial sepsis and immediate therapeutic interventions.

Joint health depends largely on conscientious management of exercise, including frequency and intensity of athletic bouts, and the provision of high-quality nutritional supplements formulated specifically for joint support. While synovial sepsis typically develops from injuries that compromise the joint capsule, it can occur following routine intraarticular injection of hyaluronic acid and corticosteroids, though the incidence of infection is uncommon.^° The prophylactic use of joint supplements in high-performance horses and prospects can delay the need for joint injections, thus postponing any risk associated with invasive procedures.

^*Haralambus, R., A. Florczyk, E. Sigl, S. Gultekin, C. Vogl, S. Brandt, M. Schierer, C. Gamerith, and F. Jenner. 2021. Detection of synovial sepsis in horses using enzymes as biomarker. Equine Veterinary Journal. In press.

^°Steel, C.M., R.R. Pannirselvam, and G.A. Anderson. 2013. Risk of septic arthritis after intra-articular medication: A study of 16,624 injections in Thoroughbred racehorses. Australian Veterinary Journal 91(7):268-273.

Can Foals With Septic Arthritis Go On To Successful Racing Careers?

Drs. Thomas O'Brien, Sarah Rosanowski, Keith Mitchell, Joan Carrick, Troy Butt and Angus Adkins completed a retrospective study of 114 Thoroughbred foals that had septic arthritis and compared them to their maternal siblings.

Foals involved with the study had undergone treatments for septic arthritis over a 6-year period. These treatments included arthroscopic, cannulae or through-and-through needle lavage. The stifle joint was the most affected (35 percent of foals), with hocks (20 percent affected) not far behind.

In total, 130 synovial fluid samples were cultured; bacterial growth was detected in 80 percent of samples. Thirty-nine of the foals needed repeat lavage of the synovial joint structure to clear the infection.

Overall, 90 foals were discharged alive (78 percent). Foals that were less than 26 days old when they were admitted were five times less likely to be discharged alive. Foals that were also afflicted with multisystemic disease were six times less likely to be discharged alive.

The researchers found that 67 percent of foals discharged alive started in one or more races; there was no difference in the proportion of foals that started or in racing performance between foals that had been treated for septic arthritis and their maternal siblings.

The scientists conclude that the prognosis for the survival of foals with septic arthritis is good and that future racing performance does not seem to be affected by this infection.

Read the published piece here.

Anthrax And Equines: A Deadly Combination

Though anthrax may be more familiar to people for its use as a biological weapon, the bacteria should also be a concern to equine owners for the potential harm, including death, it can cause to their animals.

Bacillus anthracis, the bacteria that causes anthrax, can lie dormant in soil for years; it is particularly hardy in alkaline soil. If anthrax spores are inhaled or ingested, or if they encounter a wound, horses can develop and anthrax infection. Ingestion is the most common way for horses to get an anthrax infection. Ingestion often occurs after a heavy rain, when anthrax spores are pushed to the surface of grass; it can also occur during drought conditions when grasses are eaten down to the soil.

Once anthrax enters the body, it becomes active and multiplies rapidly, causing toxins that spread throughout the body. The septicemia anthrax causes progresses rapidly; killing many affected animals within two to four days.

Horses with anthrax will have trouble breathing; they will also have a high fever, and swelling on the neck and chest. Affected horses may colic, have bloody diarrhea or have seizures. The disease can be spread to humans, so an anthrax infection must be reported to the state's veterinarian.

Anthrax is not endemic to all parts of the United States, so the vaccine is recommended only for horses that live in areas that are known to have anthrax spores. It is a live vaccine, so reactions to the injection site may occur. Antimicrobials may interfere with the vaccine response, so they should not be administered at the same time.

Read the AAEP's anthrax guidelines here.