Metronidazole for dogs and gastrointestinal tract infections
Metronidazole for dogs: indications
- In the treatment of gastrointestinal tract infections caused by Giardia spp. and Clostridium spp. (e.g., C. perfringens or C. difficile). It is also used to treat chronic diarrhoea associated with inflammatory bowel disease and granulomatous enterocolitis.
- In the treatment of urogenital tract and skin infections caused by obligate anaerobes (e.g., Clostridium spp.) sensitive to metronidazole.
With respect to its use for diarrhoea in dogs with chronic inflammatory enteropathies, above all antibiotic-responsive diarrhoea (ARD), the problem is caused by bacterial overgrowth in the anterior portion of the intestine. These bacteria are not pathogenic, but they do cause bowel dysfunction. Treatment involves empiric, broad-spectrum antibiotic therapy since the bacterial population changes from week to week. The aim is to reduce the number of bacteria, as it is impossible to sterilise the digestive tract completely. A combination of enrofloxacin and metronidazole can be used in animals with a severe condition requiring a rapid effect. It is important to use a high-quality elimination diet to improve the effectiveness of the treatment. Cases of diarrhoea can also benefit by changing the type of diet
The recommended oral dose of metronidazole is 50 mg/kg of body weight/day for 5 to 7 days. The daily dose can be divided equally and given twice a day (i.e., 25 mg/kg of body weight twice a day).
Mechanism of action
Metronidazole for dogs acts against protozoa and anaerobic bacteria, with activity against most anaerobic gram-negative bacilli, anaerobic spore-forming gram-positive bacilli and anaerobic cocci. In terms of antiparasitic activity, metronidazole is active against Trichomonas, Giardia and amoebas, including Tritrichomonas foetus, Trichomonas gallinae, Giardia lamblia and Histomonas meleagridis.
Nitroimidazols must be activated by sensitive microorganisms in order to exercise their antimicrobial action. This activation requires an anoxic or hypoxic environment, so it is done in the presence of anaerobic or microaerophilic microorganisms. Once inside the microorganism, the nitro group accepts electrons from the electron carrier proteins generated by anaerobic respiration. These electron carriers have an unusually negative redox potential and, therefore, a strong reducing capacity which facilitates the reduction of the nitro group in nitroimidazols. This reduction, carried out inside sensitive microorganisms, generates chemically reactive intermediates that can cause cell damage by reacting with macromolecules, such as DNA, where it ruptures nucleic acid strands.
Side effects and precautions
With regard to precautions, metronidazole should not be used in animals with hypersensitivity or an allergy to the medicinal product. It should be used with caution in very weak or pregnant animals and is contraindicated in animals with liver disease. Due to its hepatic metabolism, metronidazole is susceptible to enzymatic inhibition, which may occur when coadministered with cimetidine. Phenobarbital, prednisolone and rifampicin may induce oxidative metabolism of metronidazole.
The side effects of metronidazole include lethargy, weakness, liver disease, neurological disorders, neutropaenia and gastrointestinal disorders such as vomiting and lack of appetite.
Prolonged use or overdose may result in major neurological problems including nystagmus, ataxia, head nodding, disorientation, tremors, seizures and rigidity.
