Chemical structure and origin
The chemical structure of all aminoglycosides is based on a cyclic alcohol (aminocyclitol) attached to aminosugars via glycosidic bonds. An important physicochemical property of these molecules is their high polarity.
Historically, drugs of this group are obtained from natural sources—actinomycetes of the genus Actinomyces (yielding the suffix "-mycin") and Micromonospora (also yielding the suffix "-mycin"). However, amikacin is a semi-synthetic drug.
To understand the evolution of the group, it is important to remember the generation-based classification:
- 1st generation: streptomycin, neomycin, kanamycin.
- 2nd generation: gentamicin, tobramycin, netilmicin.
- 3rd generation: amikacin.
Mechanism of action and overcoming resistance
The general mechanism of action for the entire aminoglycoside group is the inhibition of protein synthesis in the bacterial cell.
Drugs within the group share similar properties but differ in their spectrum of activity and resistance profile. The key advantage of amikacin lies in its mechanism of overcoming resistance: it is not degraded by bacterial enzymes that inactivate second-generation aminoglycosides. Due to this, it successfully acts against Gram-negative bacteria resistant to gentamicin or tobramycin.
Spectrum of activity and indications
Amikacin has the broadest spectrum of activity among all aminoglycosides. Two main directions of its use are distinguished:
- Severe bacterial infections: Prescribed for diseases caused by multidrug-resistant flora. The drug has a strict clinical status—it is a reserve drug. It is conserved and used sparingly to prevent the development of widespread microbial resistance.
- Tuberculosis: Amikacin belongs to the category of antituberculosis antibiotics (alongside streptomycin, kanamycin, rifampicin, etc.). It exhibits specific activity against Mycobacterium avium. It is used for newly diagnosed pulmonary tuberculosis and lesions of other organs.
Important: Mycobacterium resistance to aminoglycosides develops rapidly, so they must be used strictly in combination with other antituberculosis agents (both antibiotics and synthetic drugs such as isoniazid or PAS).
Side effects
Like other members of the group, amikacin exhibits pronounced toxicity. First and foremost, one must be cautious of ototoxicity (damage to the auditory apparatus). When choosing therapy, it should be taken into account that among aminoglycosides, the second-generation drug netilmicin has the least pronounced ototoxic effect.
Formulations and prescription guidelines
Due to the high polarity of their molecules, aminoglycosides are practically unabsorbed in the gastrointestinal tract. Therefore, the routes of administration for amikacin are exclusively parenteral: intramuscular and intravenous.
The drug is available in vials in dosages of 0.1, 0.5, and 1.0 g. The standard administration dose is 0.5 g.
Prescription example: Rp.: Amikacini sulfatis 0.5 D.t.d. N. 10 S. Intramuscularly, 0.5 g twice daily (after preliminary dissolution in water for injections).
Briefly: answers to topical questions
To which subunit of the bacterial ribosome does amikacin bind to disrupt protein synthesis?
Amikacin binds to the 30S subunit of the bacterial ribosome. As a representative of the aminoglycoside group, to reach this target, the drug first penetrates the bacterial cell wall via passive diffusion. Then it undergoes active transport across the cytoplasmic membrane into the cell. Binding to the ribosome leads to disruption of protein synthesis, which provides the antibacterial effect of the drug.
What side effects, besides ototoxicity, are characteristic of amikacin?
In addition to ototoxicity, nephrotoxicity and vestibulotoxicity are characteristic of amikacin.
- Nephrotoxicity: listed as a risk for amikacin; if it develops, it is recommended to determine creatinine clearance and electrolyte levels, ensure adequate hydration, treat electrolyte imbalances, discontinue the injectable drug, and adjust the doses of other drugs based on creatinine clearance.
- Vestibulotoxicity: amikacin is listed among the drugs causing this reaction. In case of early symptoms, such as transient dizziness and a sensation of "ear fullness," it is recommended to reduce the amikacin dose or prescribe an intermittent regimen, consult an otorhinolaryngologist, and provide symptomatic therapy; if the disorders persist or worsen, the drug is discontinued.
Against which specific species of Gram-negative bacteria is amikacin most active?
Amikacin exhibits high activity against *Pseudomonas aeruginosa* and various enterobacteria.
- Pseudomonas aeruginosa (Pseudomonas aeruginosa) — the drug has high activity and is used in combination with other antibiotics.
- Enterobacteria (Enterobacterales) — this group includes *Escherichia coli* (Escherichia coli), klebsiellae (Klebsiella), and other pathogens.
Furthermore, due to resistance to inactivating bacterial enzymes, amikacin effectively acts against Gram-negative bacteria resistant to second-generation aminoglycosides.
What are the absolute contraindications to prescribing amikacin?
An absolute contraindication to prescribing amikacin is the presence of diabetic nephropathy in the patient. Aminoglycoside drugs (including amikacin, gentamicin, tobramycin, and netilmicin) are strictly prohibited in patients with diabetes mellitus, even at the earliest manifestations of renal damage. Prior to prescribing systemic antibiotics to such patients, a preliminary assessment of renal nitrogen-excreting function is mandatory.
With which specific drugs is amikacin combined in the treatment of tuberculosis?
In the treatment of drug-resistant tuberculosis, amikacin is classified as a second-line / Group C drug and may be included in regimens if the regimen cannot be constructed solely from Group A and B drugs.
According to MDR-TB treatment regimens in children, amikacin is listed among additional drugs:
- In pre-XDR TB: core drugs include bedaquiline, linezolid, cycloserine; among additional TB drugs are delamanid, amikacin, PAS, ethionamide/prothionamide, ethambutol, pyrazinamide, clofazimine.
- In XDR TB: core drugs include linezolid/bedaquiline, cycloserine, delamanid, ethambutol, pyrazinamide; among additional TB drugs are meropenem + amoxicillin + clavulanic acid, ethionamide/prothionamide, PAS, amikacin, clofazimine.
Amikacin — an AMInoglycoside with Active Mycobacterial (*Mycobacterium avium*) protection. The Roman numeral III in the word "amIIIkacin" serves as a reminder of the 3rd generation.
Class and exam questions
Why is amikacin effective against bacteria resistant to gentamicin?
Amikacin is not degraded by bacterial enzymes that inactivate second-generation aminoglycosides (which include gentamicin).
Can amikacin be prescribed in tablet form?
No. Aminoglycoside molecules are highly polar, therefore they are not absorbed in the GI tract. The drug is administered exclusively parenterally.
What is the clinical status of amikacin and why?
This is a reserve drug. It is prescribed only for severe infections with multidrug-resistant flora to prevent the development of global bacterial resistance.
How can the rapid development of mycobacterial resistance to the drug be prevented?
In the treatment of tuberculosis, amikacin (like streptomycin) must be used strictly in combination with other antituberculosis agents.
What else to study on this topic
- Mechanisms of enzymatic inactivation of aminoglycosides by the bacterial cell.
- Comparative characteristics of ototoxicity among 1st, 2nd, and 3rd generation drugs.
- Principles of combination therapy for pulmonary tuberculosis and the place of antibiotics in treatment regimens.
- Features of opportunistic infections caused by *Mycobacterium avium*.
- Pharmacokinetics of highly polar molecules upon parenteral administration.
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