Aminoglycosides Explained: Definition, Types & Applications

Traditional Gram-negative antibacterial drugs that inhibit protein synthesis and contain an amino-modified glycoside as part of the molecule are classified as aminoglycosides (sugar). The word may also apply to any organic molecule with amino sugar substructures in a broader sense. Antibiotics that are aminoglycosides have bactericidal activity against Gram-negative bacteria and some anaerobic bacteria where resistance has not yet developed, but not against Gram-positive or anaerobic Gram-negative bacteria.

Streptomycin aminoglycoside is the first type of antibiotic. It is derived from Streptomyces griseus and was the first modern tuberculosis treatment. Streptomycin lacks the 2-deoxystreptamine moiety found in most other members of this class. The deoxystreptamine-containing antibiotics kanamycin, tobramycin, gentamicin, and neomycin are examples of aminoglycosides.

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Sar of Aminoglycosides:

Streptomycin, neomycin, gentamicin, paromomycin, sisomicin, ribostamycin, tobramycin, nebramycin, dibekacin, amikacin, and kanamycin are all aminocyclitol-containing antibiotics. Streptomyces and Micromonospora species produce them.

Mechanism of Action:

They only need a brief contact period and are most successful against rapidly multiplying susceptible bacterial populations. While additional mechanisms are implicated for some particular agents, and/or detailed mechanistic explanations are currently unavailable, these activities are attributed to a primary mode of action as protein synthesis inhibitors.

The energy-dependent, often irreversible binding of aminoglycosides to the cytosolic, membrane-associated bacterial ribosome inhibits protein synthesis. Although the specific steps in protein synthesis affected, as well as their affinity and degree of binding, aminoglycoside presence in the cytosol generally disrupts peptide elongation at the 30S ribosomal subunit, resulting in inaccurate mRNA translation and, as a result, biosynthesis of proteins that are truncated or have altered amino acid composition. 

Binding, in particular, impairs translational proofreading, resulting in RNA message misreading, premature termination, or both, and thus inaccuracy of the translated protein product. The bacterial cell membrane's permeability can change as a result of the aberrant proteins incorporated into it, leading to "further stimulation of aminoglycoside transport." The amino sugar part of this class of molecules is involved in the small molecule's interaction with ribosome structures, which leads to translation infidelity.

Types of Aminoglycosides

There are several different antibiotics in the aminoglycoside class. The US Food and Drug Administration (FDA) has approved gentamicin, tobramycin, amikacin, plazomicin, streptomycin, neomycin, and paromomycin for clinical use in the United States.

Amikacin Aminoglycoside: Amikacin is a semisynthetic derivative of kanamycin that is made by acetylating 1-amino.

Kanamycin A maintains about half of its original activity against Gram-ve bacilli after an acylamino substitution (L-HABA).

Amikacin is more active when combined with L-HABA than when combined with DHABA.

Unlike gentamicin and tobramycin, amikacin is resistant to most aminoglycoside inactivating enzymes.

Amikacin is Only Susceptible to Enzymes that:

1. Acetylate 6′-NH₂

2. Phosphorylate 3′-OH

3. Adenylate 4′-OH

Vancomycin Aminoglycoside: Antibiotics that inhibit bacterial cell wall biosynthesis, such as -lactams and vancomycin, have a synergistic effect with aminoglycosides. Finally, aminoglycosides have pharmacokinetic properties that are relatively predictable, allowing them to be dosed to mitigate their intrinsic toxicity.

Oral Aminoglycoside: Since aminoglycosides are poorly absorbed when taken orally, they are usually administered parenterally, either intravenously or intramuscularly.

Clinical Use

The recent appearance of infections caused by Gram-negative bacterial strains with advanced antimicrobial resistance trends has led doctors to reconsider their use of these antibiotics.  This renewed interest in aminoglycosides has reignited controversy about the two major issues surrounding these compounds, namely their antimicrobial susceptibility spectrum and toxicity. 

Despite this, the relatively common incidence of nephrotoxicity and ototoxicity during aminoglycoside care makes physicians wary of using these drugs in routine practice.

Common Side Effects:

Aminoglycosides are extremely powerful antibiotics with serious side effects, particularly when taken orally or intravenously.

The FDA has given black-box warnings for aminoglycosides taken orally or intravenously, citing the following potential side effects:

• Hearing loss is caused by damage to the ear's hearing structures.

• Damage to the inner ear causes difficulty keeping one's balance.

• Harm to the kidneys (noted by protein in the urine, dehydration, and low levels of magnesium)

• Skeletal muscle paralysis

Inner ear toxicity caused by aminoglycosides may result in sensorineural hearing loss. Inner ear toxicity occurs in 7 to 90% of patients, depending on the antibiotics used, the patient's sensitivity to such antibiotics, and the length of antibiotic treatment.

Vestibular ototoxicity is another severe and debilitating side effect of aminoglycoside use. This causes oscillopsia (gaze instability) and balance problems, which affect every aspect of antigravity operation. This is a lifelong loss that can occur at any dosage.

Although the magnitude of side effects varies from person to person, the higher the dosage or the longer the time of use of an aminoglycoside, the greater the risk of side effects.

Warnings and Precautions:

If you're allergic to aminoglycosides or any of the inactive ingredients in these products, stay away from them.

If you have any of the following conditions, you can talk to your doctor about aminoglycosides:

• Have kidney or hearing issues, as well as balance issues and uncontrollable eye movements?

• Have a nerve and muscle dysfunction, such as multiple sclerosis or myasthenia gravis.

• If you are 65 years old or older.

• You have a newborn or a very young child who will need to be treated with aminoglycosides for a severe infection.