Gentamicin is an aminoglycoside antibiotic. It is primarily effective against Gram-negative bacteria but is now used systemically only in emergencies because of nephrotoxic and ototoxic side effects.
What is gentamicin?
Gentamicin is an antibiotic from the group of aminoglycosides, which is composed of several substances called gentamicins. It is thus a mixture of substances. The sulfate salt of gentamicin is used as the drug. The first gentamicins were discovered in the bacterial strain Micrononospora purpurea. The various gentamicins are structurally very similar. Gentamicin has a bactericidal effect and is mainly effective against Gram-negative bacteria, but also against staphylococci. It is used systemically only as a reserve antibiotic, especially in nosocomial infections (so-called hospital infections), because it can cause severe side effects. Nephro- and ototoxicity are the main ones to be mentioned here. When used topically, these possible side effects are so unlikely that they are negligible. For this reason, gentamicin is commonly used in eye drops and eye ointments.
Pharmacologic action
Gentamicin is a well-acting antibiotic and can be used to treat various bacterial infections. In practice, gentamicin is used systemically only as an emergency medication because it can cause severe side effects. These include, above all, pronounced nephro- and ototoxicity. These potential renal and ototoxic effects prevent widespread use of gentamicin as long as other effective antibiotics are available. However, for some indications, especially hospital-acquired infections (nosocomial infections), other agents are often unavailable or the other antibiotics available cause similar or more severe side effects. In veterinary medicine, on the other hand, gentamicin is widely used, mainly due to its low price. The mechanism of action of gentamicin is to prevent the reading of mRNA on the ribosomes of bacteria. This is done by binding to the 30S subunit of the ribosomes. If the mRNA cannot be read, the protein biosynthesis of the bacteria is impeded. If a high concentration of gentamicin is present, human protein biosynthesis can also be affected. When applying gentamicin, it should be noted that this cannot be done orally. Gentamicin must always be applied parenterally.
Medical application and use
Gentamicin is primarily effective against Gram-negative bacteria, but it is also effective against staphylococci. It is not effective against anaerobic bacteria, and gentamicin is less effective in acidic and/or anaerobic environments. In general, gentamicin is a well-performing antibiotic and thus could be used for a number of bacterial infections. However, because there is a high risk of severe side effects, systemic use of gentamicin is done only in emergencies. In such cases, it is usually used in combination with beta-lactam antibiotics. Indications for the use of gentamicin include endocarditis (inflammation of the inner lining of the heart), severe infections caused by pseudomonas, enterococci, listeria, staphylococci, and enterobacteria, as well as infections caused by multiply resistant tuberculosis bacteria. In any case, the systemic use of gentamicin must be strictly weighed against the risk of severe side effects. In the case of prolonged treatment, this weighing must take place again and again. The therapeutic range of gentamicin is narrow: if an elevated plasma level exists, the risk of nephro- and ototoxic reactions increases rapidly. The risk also increases with increasing duration of treatment, as gentamicin accumulates in the renal cortex. Thus, strict indication and individualized dosing are necessary. With topical application, the risk of systemic side effects is low. For this reason, gentamicin is frequently used in eye drops and ointments. In surgery, ball chains containing gentamicin and bone cement containing gentamicin are sometimes used to prevent postoperative soft tissue and bone infections. In addition, sponges containing gentamicin are used in various procedures. Gentamicin is useful here because of its high heat resistance and low allergenic potential. Gentamicin can also be used against Meniere’s disease, but is not approved for this use.The vertigo that occurs in Meniere’s disease can be treated with gentamicin because gentamicin can destroy sensory cells in the ear due to its ototoxicity.
Risks and side effects
Gentamicin is highly nephro- and ototoxic. In 1-10% of cases, damage to the kidney occurs due to gentamicin. In this case, damage to the proximal tubule occurs. This is usually reversible. In combination with other nephrotoxic drugs, the risk increases. Ototoxic reactions also occur frequently. Hearing damage occurs in 1-3% of cases, and balance disorders occur in up to 14% of cases. There is no safe gentamicin dose, but the risk of side effects increases with a higher daily dose and with a higher total dose. Thus, there is a higher risk with a longer duration of treatment and with a higher dose. Other side effects consist of neuromuscular blockages. Plasma levels must be monitored during treatment with gentamicin.
