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Gentamicin can be found in the form of an ointment, cream, sponge soaked in this antibiotic, infusion solution and in eye drops. Gentamicin is most often used in inpatient treatment, i.e. in hospitals. At the pharmacy, the patient can buy prescription eye drops containing this antibiotic, or ointments or creams with gentamicin as one of the ingredients (usually accompanied by a corticosteroid or other antimicrobial substance, such as clotrimazole). There is no oral form of gentamicin as this substance is not absorbed from the gastrointestinal tract.

Gentamicin in action

Gentamicin is one of the antibacterial drugs from the group of aminoglycosides. Its action is bactericidal and is based on binding to the subunits of bacterial ribosomes. As a result, it inhibits the synthesis of normal proteins in the bacterial cell, and in their place, proteins with the wrong amino acid sequence are formed.

The process of penetration of the gentamicin molecule into the bacterial cell is disturbed in conditions of increased osmolarity, at lower pH or in the presence of increased concentrations of calcium and magnesium in the body. These conditions favor the relative resistance of bacteria to gentamicin.

The scope of gentamicin activity is quite wide and includes:

  • Gram negative aerobic bacteria,
  • staphylococci,
  • Listeria myynocytogenes bacteria
  • and some Gram positive bacteria, e.g. Staphylococcus epidermidis, Staphyloccocus saprophyticus.

Initially, gentamicin was used with great optimism by clinicians, but with time its toxic effects on the kidneys and hearing organs were noticed. Following the introduction of newer and safer antibiotics, gentamicin has ceased to be used as often. However, due to the increasing resistance of bacteria to the new drugs, the medical community was again leaning towards the treatment of severe infections with gentamicin.

There are assumptions that the limited use of gentamicin, only in the case of severe diseases caused by bacteria sensitive to aminoglycosides, reduces the risk of resistance to the previously mentioned. It is said that the temporary discontinuation of gentamicin in the hospital reduces bacterial resistance, which means that after some time it is possible tosuccessfully initiate treatment with this substance.

To reduce the occurrence of toxic side effects, it is recommended that the patient's serum gentamicin concentration is monitored during therapy.

This substance is characterized by the inter-individual variability of pharmacokinetic parameters and the fact that even a slight deterioration of the condition of the kidneys in a patient affects the metabolism of gentamicin.

Intravenous infusions

There are unofficial regimens for treating patients with intravenous infusions of gentamicin in combination with other antimicrobial agents, where gentamicin is administered only once a day. This combination of two different antibiotics increases the effectiveness of the treatment and reduces the risk of side effects caused by long-term gentamicin therapy.

Currently, to treat infections in hospitals, gentamicin is always given with another antibiotic.

Gentamicin-soaked sponge

The use of a gentamicin-soaked sponge is common in surgery, orthopedics and transplantation . Placing a sponge inside the wound after surgery or as a protection with a sponge on the implant after implantation is to reduce the risk of infection, i.e. it is preventive.

A sponge once placed in a wound stays there permanently and is not removed. The sponge itself is made of type I and III collagen, thanks to which it is completely resorbed at the application site.

This form of gentamicin administration cannot, however, be the only antibacterial activity if the patient is infected. In this case, in addition to the sponge, specialists also recommend the inclusion of general antibacterial drugs in the therapy.

Drops or ointment

Gentamicin in the form of eye drops or ointments is considered safe and carries no such risk of side effects.

From the conjunctival sac, gentamicin is practically not absorbed in inches, therefore it does not show any systemic effects.

The same poor absorption is seen when this antibiotic is applied to the ear.

Indications for the use of gentamicin

Surgery, orthopedics and transplantation using a gentamicin 2 mg / cm2 sponge:

  • Supportive treatment of infections caused by gentamicin-sensitive bacteria. It is worth mentioning here that in the case of postoperative infection, the best solution is to perform a bacteriogram and select an appropriate antibiotic based on it.
  • Prevention of local infections of bones and soft tissues and after implantation.

In ophthalmology in the form of drops:

  • Acute and chronic bacterial conjunctivitis,the edge of the eyelids or the lacrimal sac.
  • Ulceration and keratitis due to bacterial infection.
  • Prophylactically after surgery.

In dermatology:

  • Gentamicin in combination with corticosteroids is most commonly used to treat exudative skin inflammations that have been secondarily infected with gentamicin-sensitive bacteria.

In the form of an injection or infusion in a hospital setting:

  • Serious infections due to Gram-negative aerobes, including:
    • sepsis,
    • an intra-abdominal infection such as a peritoneal infection
    • abscesses or inflammation of the bile ducts,
    • urinary tract infections,
    • respiratory tract infections,
    • secondary burn infections,
    • postoperative infections,
    • severe infections in newborns (gentamicin in combination with ampicillin is one of the recommended combinations in the event of sepsis in infants).

Gentamicin dosage

Dosing of the injection solution is prescribed by the attending physician. It usually works according to the guidelines included, among others, in the "National Antibiotic Protection Program."

Dose adjustments are necessary in patients with renal insufficiency or diminished function. Caution should be exercised in setting the treatment regimen in patients who are taking concomitant medications that burden the kidneys, such as diuretics, and in elderly patients.

Patients with normally functioning kidneys usually administer gentamicin once a day. Gentamicin eye drops are usually applied every 4 hours for 1-2 drops.

The gentamicin sponge is usually applied focal or on the skin by the surgeon after the procedure.

Gentamicin ointment is used in adults and children over 12 years of age, usually once or twice a day.

The patient should always follow the instructions of the doctor who prescribes the antibiotic. The patient should not modify the treatment regimen on his own, as this increases the risk of ineffectiveness of therapy or the development of resistance to bacteria that cause the infection, or, ultimately, secondary infection with already resistant microorganisms, such as fungi or bacteria.

Contraindications to the use of gentamicin

Usually the only contraindication to the use of gentamicin is hypersensitivity to this substance or hypersensitivity to other aminoglycosides.

In some sources, myasthenia gravis is mentioned as a contraindication to gentamicin treatment.

Precautions and drug interactions

Since gentamicin therapy carries a risk of damage to the kidneys or hearing, it is recommended to monitor its concentration in the patient's serum in order to avoid side effects. Often the patient is also checked for renal function (serum creatinine, creatinine clearance), as well as the functions of the vestibule and cochlea located in the hearing organ.

Gentamicin can also damage the equilibrium organ and inhibit neuromuscular transmission.

Ototoxicity, i.e. hearing damage, is a threat mainly to children, the elderly and patients with kidney failure, because in their case gentamicin can accumulate in the body.

Renal impairment usually goes away after treatment ends. In most cases, nephrotoxicity is caused by several factors, either together or separately:

  • long treatment with gentamicin,
  • with an increased dose of the drug,
  • the patient has previous kidney problems
  • and the patient taking other nephrotoxic drugs.

Patients with hypocalcaemia should be treated with gentamicin with caution. If you suffer from muscle weakness or have Parkinson's disease, the neuromuscular transmission may be blocked after gentamicin is given. To avoid this side effect, administer the drug slowly intravenously.

If you are taking neuromuscular blocking drugs concomitantly, you may experience increased blockage, which could result in respiratory arrest. The antidotes in this situation are calcium and neostigmine.

If you experience diarrhea for a long time during treatment, you may have developed pseudomembranous enteritis after antibiotic treatment. In this situation, treatment should be discontinued and drugs that respond to C. difficile should be instituted. Medicines that inhibit intestinal peristalsis should under no circumstances be administered to the patient.

The infusion solution is sodium metabisulfate, methyl parahydroxybenzoate and propyl parahydroxybenzoate, which may cause allergic reactions in some patients.

Gentamicin should not be administered together with oto-, neuro- and nephrotoxic drugs as the risk of these side effects increases.

Side effects

Gentamicin is toxic to:

  • hearing organs,
  • vestibular system,
  • kidneys
  • and inhibits neuromuscular conduction.

Other activitiesundesirable is:

  • hypersensitivity reactions,
  • increased body temperature,
  • proteinuria,
  • headaches,
  • fatigue,
  • paresthesia,
  • visual disturbance,
  • palpitations,
  • increased levels of bilirubin, urea and creatinine in the plasma.

Hearing and vestibular disturbances are rare but serious as they are usually irreversible. They usually occur when gentamicin levels are consistently elevated in the patient's plasma.

At first, the patient hears high frequencies incorrectly, followed by tinnitus and a feeling of pressure in the ears. Vestibular disorders are usually manifested by nausea, vomiting, dizziness and nystagmus.

With eye drops, corneal calcification is sometimes observed due to the presence of phosphate in the drop formula.

May also occur:

  • tearing,
  • eye redness,
  • pain,
  • itchy feeling,
  • pruritus,
  • and after instillation, the patient may experience photophobia for several minutes.

When the patient uses gentamicin eye drops for a long time, it may lead to corneal ulceration due to fungal infections or caused by gentamicin-resistant bacteria.

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