How gentamicin works
Gentamicin is an antibiotic agent that is used only when standard antibiotics no longer work. A doctor prescribes gentamicin primarily for severe bacterial infections (e.g., urinary tract infections). The active substance inhibits the formation of membrane proteins in the bacteria and thus kills them.
The substance deposits particularly well in bacterial species with a special wall structure. The active ingredient enters the interior of a bacterium through channels in the cell wall known as porins. There it binds to a subunit of the RNA – a genetic sequence that contains the information for the production of proteins.
This leads to errors in the reading of this information and subsequently to the formation of defective proteins. These are now incorporated into the cell membrane of the bacterium, facilitating the penetration of further gentamicin. This process leads irrevocably to the death of the pathogen.
Aminoglycoside antibiotics such as gentamicin also impart a post-antibiotic effect, meaning that they continue to inhibit bacterial growth even after the concentration has already fallen below the minimum inhibitory concentration (MIC; lowest concentration of an antibiotic at which bacterial growth is still inhibited).
Absorption, degradation and excretion
Since gentamicin cannot be absorbed through the intestine, in most cases it is introduced directly into the bloodstream by infusion. From there, it enters the tissues.
Gentamicin is not broken down by the body, but is excreted unchanged by the kidneys. On average, two to three hours after administration, half of the active substance has left the body.
When is gentamicin used?
Gentamicin is used in the following cases:
- bacterial infections of the urinary tract, abdomen, eye, skin, and soft tissues
- @ after surgical interventions
Locally, for example in the form of eye drops or ointments, gentamicin is used for the following indications:
- Inflammations of the anterior segment of the eye with gentamicin-sensitive pathogens
- ulcus cruris (ulcer of the lower leg) and decubitus (bedsores)
How gentamicin is used
Gentamicin is often administered to patients as an injection solution. This usually involves diluting the drug in a small amount of an infusion solution to better distribute it in the blood. If kidney function is normal, a dose of 3 to 6 milligrams per kilogram of body weight (mg/kg bw) is given once a day. A maximum daily dose of 6 mg/kg may be required to treat severe infections or when the pathogen shows only reduced sensitivity to the agent.
The effect of a single dose administered intravenously lasts for a long time, which is why gentamicin only needs to be given once daily.
If inflammation is present at the same time, the antibiotic can also be combined with a glucocorticoid (“cortisone”). Ready-made combination preparations are available for this purpose.
Contact lenses should not be worn during treatment with gentamicin eye drops or gentamicin eye ointment.
What are the side effects of gentamicin?
Common side effects of gentamicin treatment include eye disease, which is characterized by burning and redness of the eye. In addition, damage to the hearing (inner ear) may occur, not only affecting hearing but often causing loss of balance.
Kidney damage is also possible with gentamicin. However, by stopping the drug immediately, kidney dysfunction can usually be reversed.
Occasionally, skin rashes, muscle pain and an increase in body temperature can also be consequences of treatment with gentamicin.
When should gentamicin not be used?
Contraindications
Gentamicin must not be used in:
- known hypersensitivity to the active substance or other aminoglycoside antibiotics
- Myasthenia gravis (pathological muscle weakness)
Interactions
Since gentamicin can interfere with the transmission of impulses from motor nerves to the muscle, use of the active substance in patients with previous neuromuscular diseases is recommended only under medical supervision. The reason: this disruptive effect can be intensified by muscle-relaxing drugs (muscle relaxants) to such an extent that breathing difficulties or even respiratory paralysis are possible.
The simultaneous use of drugs that can also cause inner ear and kidney damage as a side effect (e.g. other aminogycosides, amphotericin B, ciclosporin, cisplatin) increases these side effects.
Age Limitation
When indicated, gentamicin may be administered as early as infancy.
During pregnancy, intravenous gentamicin should only be used in the case of life-threatening infections. If this is the case, it is advisable to check the child’s hearing performance at an early stage. Local application (e.g., as gentamicin ophthalmic ointment) is acceptable during pregnancy because the active ingredient is not absorbed to any appreciable extent.
Gentamicin passes into breast milk after intravenous administration. Most breastfed infants do not develop symptoms as a result. In individual cases, thin stools, rarely diarrhea, may occur. Therefore, if intravenous gentamicin is indicated during the breastfeeding period, breastfeeding may continue. Local application as ointment or eye drops is not problematic.
How to obtain medicines containing gentamicin
Gentamicin is available in Germany, Austria and Switzerland in all dosage forms only with a prescription at the pharmacy.
