Gentamicin is an aminoglycoside antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis among others. It can be given intravenously, by intramuscular injection, or topically. Topical formulations may be used in burns or for infections of the outside of the eye. It is often only used for two days until bacterial cultures determine what specific antibiotics the infection is sensitive to. The dose required should be monitored by blood testing. Gentamicin can cause inner ear problems and kidney problems. The inner ear problems can include problems with balance and hearing loss. These problems may be permanent. If used during pregnancy, it can cause harm to the developing fetus. However, it appears to be safe for use during breastfeeding. Gentamicin is a type of aminoglycoside and works by disrupting the ability of the bacteria to make proteins, which typically kills the bacteria. Gentamicin is naturally produced by the bacterium Micromonospora purpurea, was patented in 1962, approved for medical use in 1964. The antibiotic is collected from the culture of the Micromonospora by perforating the cell wall of the bacterium. Current research is underway to understand the biosynthesis of this antibiotic in an attempt to increase expression and force secretion of gentamicin for higher titer. Gentamicin is on the World Health Organization's List of Essential Medicines. The World Health Organization classifies gentamicin as critically important for human medicine. It is available as a generic medication.
Medical uses Gentamicin is active against a wide range of bacterial infections, mostly Gram-negative bacteria including Pseudomonas, Proteus, Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes, Serratia, and the Gram-positive Staphylococcus. Gentamicin is used in the treatment of respiratory tract infections, urinary tract infections, blood, bone and soft tissue infections of these susceptible bacteria. There is insufficient evidence to support gentamicin as the first line treatment of Neisseria gonorrhoeae infection. Gentamicin is not used for Neisseria meningitidis or Legionella pneumophila bacterial infections (because of the risk of the person going into shock from lipid A endotoxin found in certain Gram-negative organisms). Gentamicin is also useful against Yersinia pestis (responsible for plague), its relatives, and Francisella tularensis (the organism responsible for tularemia often seen in hunters and trappers). Some Enterobacteriaceae, Pseudomonas spp., Enterococcus spp., Staphylococcus aureus and other Staphylococcus spp. have varying degrees of resistance to gentamicin.
Special populations
Pregnancy and breastfeeding Gentamicin is not recommended in pregnancy unless the benefits outweigh the risks for the mother. Gentamicin can cross the placenta and several reports of irreversible bilateral congenital deafness in children have been seen. Intramuscular injection of gentamicin in mothers can cause muscle weakness in the newborn. The safety and efficacy for gentamicin in nursing mothers has not been established. Detectable gentamicin levels are found in human breast milk and in nursing babies.
Elderly In the elderly, renal function should be assessed before beginning therapy as well as during treatment due to a decline in glomerular filtration rate. Gentamicin levels in the body can remain higher for a longer period of time in this population. Gentamicin should be used cautiously in persons with renal, auditory, vestibular, or neuromuscular dysfunction.
Children Gentamicin may not be appropriate to use in children, including babies. Studies have shown higher serum levels and a longer half-life in this population. Kidney function should be checked periodically during therapy. Long-term effects of treatment can include hearing loss and balance problems. Hypocalcemia, hypokalemia, and muscle weakness have been reported when used by injection.
Contraindications Gentamicin should not be used if a person has a history of hypersensitivity, such as anaphylaxis, or other serious toxic reaction to gentamicin or any other aminoglycosides. Greater care is required in people with myasthenia gravis and other neuromuscular disorders as there is a risk of worsening weakness. Gentamicin should also be avoided when prescribing empirical antibiotics in the setting of possible infant botulism (Ampicillin with Gentamicin is commonly used as empiric therapy in infants) also due to worsening of neuromuscular function.
Adverse effects Adverse effects of gentamicin can range from less severe reactions, such as nausea and vomiting, to more severe reactions including:
Low blood cell counts Allergic reactions Neuromuscular problems Nerve damage (neuropathy) Kidney damage (nephrotoxicity) Ear disorders (ototoxicity) Nephrotoxicity and ototoxicity are thought to be dose related with higher doses causing greater chance of toxicity. These two toxicities may have delayed presentation, sometimes not appearing until after completing treatment.
Kidney damage Kidney damage is a problem in 10–25% of people who receive aminoglycosides, and gentamicin is one of the most nephrotoxic drugs of this class. Oftentimes, acute nephrotoxicity is reversible, but it may be fatal. The risk of nephrotoxicity can be affected by the dose, frequency, duration of therapy, and concurrent use of certain medications, such as NSAIDs, diuretics, cisplatin, ciclosporin, cephalosporins, amphotericin, iodide contrast media, and vancomycin. Factors that increase risk of nephrotoxicity include:
Increased age Reduced renal function Pregnancy Hypothyroidism Hepatic dysfunction Volume depletion Metabolic acidosis Sodium depletion Kidney dysfunction is monitored by measuring creatinine in the blood, electrolyte levels, urine output, presence of protein in the urine, and concentrations of other chemicals, such as urea, in the blood.
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