Aminoglycosides high toxicity when used parenterally. They can cause hearing loss and renal failure if used for a prolonged time. Additionally, their spectrum is mainly limited to aerobic Gram (-) bacteria. In swine, they are most commonly given orally to treat neonatal enteric disorders.
Useful molecules to know in swine medicine:
Mechanism of Action
Aminoglycosides are actively entering into the bacteria through a pump requiring oxygen as a co-factor. The antimicrobials then bind to the 30S ribosomal subunit, disrupting the translation and leading to the creation of misfolded proteins. The proteins are then embedded in the cell membrane and modify its structure, making it more porous for the antimicrobial, facilitating its entry in the bacteria and increasing the amount of dysfunctional proteins. Eventually, the bacteria’s structure is completely disrupted and the cell dies.
Check your learning: Aminoglycosides and Mechanism of Action
Aminoglycosides have a narrow spectrum. They are most efficient against aerobic Gram – bacteria. Indeed they require oxygen and an active pump to enter the bacteria. They can also be effective against Staphylococcus spp. and some Mycoplasma spp. can also be susceptible.
Aminoglycosides have a very poor bioavailability, they are not absorbed in the intestinal tract. Therefore, they are injected subcutaneously or intramuscularly for a systemic effect or they are given per os to treat enteric infections. They can also be used topically. In swine, they are mainly used orally in cases of neonatal diarrhea.
Aminoglycosides are weak bases that are water soluble.
Their volume distribution is low and they do not bind strongly to plasma proteins. Aminoglycosides, therefore, move freely systemically and do not penetrate tissues.
Aminoglycosides are not metabolized and are excreted as is through the kidneys. Their half-life is directly correlated to renal clearance. Systemic use of aminoglycosides in food animals is not recommended because of the time it takes for the antimicrobial to completely clear the renal tissue. The withdrawal times for aminoglycosides reflect this and are extremely long.
Aminoglycosides can be extremely toxic and cause renal failure. Indeed their excretion is limited by renal clearance. If the dose is higher than what can be eliminated by the kidneys, aminoglycosides accumulate in the tubular cells, causing necrosis. The effects can be reversed if the treatment is stopped early enough. They can also cause hearing loss that can become irreversible if the treatment is continued for a long time.
Resistances against aminoglycosides can either be due to a lower permeability of the bacterial membrane to the antimicrobial or to enzymes modifying the molecular structure and making it inactive.
The effect of aminoglycosides can be potentiated by beta-lactams.