Metronidazole has an important role in equine health, but many questions remain as to dosing, side-effects, and efficacy. It has a primary role in treating anaerobic and protozoal infections. It also has activity against microaerophilic bacteria, which are bacteria that prefer an anaerobic environment but can tolerate a small amount of oxygen in their environment (aka aerotolerant anaerobes). These include Vibrio species, Campylobacter species and Helicobacter species.
Mechanism of Action
The first step is to diffuse across the cell membrane of both anaerobic and aerobic bacteria, although antimicrobial activity is limited to anaerobic organisms. Metronidazole is then reduced by transport proteins leading to a concentration gradient that promotes more drug entry into the bacterial cell as well as the formation of cytotoxic free radicals. These radicals interact with host DNA causing strand breakage and destabilization of the DNA helix, and cell death.
Indications
Metronidazole is commonly added to other antibiotics to provide emergency coverage in conditions where anaerobic bacteria may be involved, for example, penicillin, gentamicin and metronidazole provides good broad-spectrum coverage in conditions such as aspiration pneumonia, pleuropneumonia, and peritonitis.
Metronidazole is often used to treat diarrhoeal diseases where Clostridium species may be involved. The classical diseases include duodenitis proximal jejunitis or acute colitis caused by Clostridium difficile, although a study from California reported that about one third of Clostridium difficile isolates were resistant to metronidazole in vitro.
The drug is also commonly used in neonatal foals to treat a range of enteric Clostridial diseases. Often these are severe infections of the small intestine, caecum and colon, frequently resulting in luminal haemorrhage.
Metronidazole use has been advocated in the management of right dorsal colitis (RDC) as it is has been postulated that certain intraluminal anaerobic bacteria, such as Bacteroides vulgatus, could perpetuate the mucosal inflammation.
Giardia and other protozoal infections are commonly sensitive to metronidazole.
The drug is also indicated in the management of clostridial myositis (gangrene, malignant oedema).
The drug has been used topically to manage pododermatitis of the frog (thrush) and bacterial dermatitis of the frog and heel bulbs (canker), using a paste formulation to pack the necrotic area covered by a foot bandage.
Side-effects and Toxicity
The most commonly observed complication of therapy is a reduction in feed intake through to total feed refusal (anorexia). In some horses diarrhea has been reported as a side-effect of treatment. It typically resolves after discontinuation and is probably related to a change in gut flora. Rare anecdotal reports of colitis (inflammation of the gut wall) have been associated with metronidazole usage.
Dosage
Dosing information is intended for use by registered veterinarians or veterinary nurses. Equiimed assumes no responsibility for the information detailed below. Equiimed shall not be liable for any damages resulting from reliance on any information provided below, or by reason of any misstatement or typographical errors. Ultimately veterinarians should consult information provided by the manufacturer prior to use.
Tags: Pharmacology