Horses are prone to a wide range of bacterial diseases. In fact, the bacterial organisms in a given horse’s environment can number in the billions per square inch.1 Fortunately, most of these are harmless, living in the soil and water. Others are beneficial, living on the horses’ skin, in the respiratory system, and in the gastrointestinal tract, where they help safeguard and complement the immune system. As with humans, in the gastrointestinal tract they aid in digestion. 

A small number of pathogenic bacterial species can cause disease in the horse if given the opportunity—such as when a horse’s structural defenses (skin) and/or its cell and chemical defenses (immune system) are compromised.2 Additionally, normally benign bacteria can become infectious in certain instances. Coliform bacteria for example, which are found in manure, can get into a fresh wound and, with time, can actively grow and give rise to disease.3 

The horse’s immune system is capable of neutralizing most bacterial infections on its own. Unfortunately, the inflammatory process can do collateral damage to healthy tissues. When a horse develops bacterial disease, the source of bacteria is usually contaminated water, food or feces. Horses often become infected with bacteria after their immune system has already been compromised by a virus. Bacterial infections are more common in horses that that travel or spend a lot of time at training stables where lots of different horses are coming and going.3 Foals and geriatric horses are much more at risk of becoming sick because their immune systems are not as strong as adult horses in their prime. Additionally, some infections can quickly grow out of control and produce devastating complications, such as septic arthritis.

Antibiotic Origins and Use

While naturally-occurring antibacterials have been used for centuries, antibiotic drugs have only been available in modern medicine for about 75 years.1 Over the past several decades, researchers have developed purified forms of naturally-occurring antibacterials as well as synthetic versions of these agents. Throughout these processes, more efficient ways of using these drugs have been devised, and new ways of combining different agents have also increased their efficacy. As a result, a number of once-feared diseases have been rendered curable. Infections that might once have crippled and/or killed horses are often easily remedied.4

Macrolide antibiotics are active against:

• Aerobic and anaerobic gram-positive cocci, except for most enterococci, many Staphylococcus aureus strains (especially methicillin-resistant strains), and some Streptococcus pneumoniae and S. pyogenes strains

• Rhodococcus equi

• Streptococcus equi

• Mycoplasma pneumoniae

• Chlamydia trachomatis

• Chlamydophila pneumoniae

• Legionella species

• Corynebacterium diphtheriae

• Campylobacter species

• Treponema pallidum

• Borrelia burgdorferi

• Haemophilus influenza

• Mycobacterium avium complex (MAC)

Macrolide antibiotics have been considered the drug of choice for group A streptococcal and pneumococcal infections when penicillin cannot be used.2 The use of macrolide antibiotics began with the discovery of erythromycin, which was isolated from soil bacteria in the early 1950's.3  Newer semi-synthetic relatives of erythromycin include claithromycin and azithromycin. Macrolide antibiotics are often used in the treatment of disease caused by the bacteria R. equi, which causes severe pneumonia in foals. Clarithromycin is considered to be the most effective drug of the three macrolide antibiotics, but an increased incidence of diarrhea is sometimes noted with its use.1

Where to buy Clarithromycin + Rifampin

Clarithromycin + Rifampin for equines is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. 

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1equusmagazine.com.

2Merck Veterinary Manual.

3Muscatello G, Leadon D, Klay M, Meijer W & Gilkerson J (2007) Rhodococcus equi infection in foals: the science of 'Rattles'. Equine Vet J 39 (5), 470-478.

4Venner, M., et. al. (2013) Comparison of tulathromycin, azithromycin and azithromycin-rifampin for the treatment of mild pnuemonia associated with Rhodococcus equi. Vet Rec 173 (16), 397.