How Effective Are Antibiotics for MRSA?

Aminoglycosides (aminoglycosides) antibiotics are composed of two or three amino sugar molecules and an amino ring alcohol called aglycon, which is a non-sugar moiety, connected by ether bonds, and are divided into two categories: natural and semi-synthetic. Natural sources include streptomycin, kanamycin, tobramycin, neomycin, and spectinomycin, which are obtained from the culture solution of Streptomyces, and Qingqing, which is obtained from the culture solution of Micromonas. Doxorubicin, sisomicin, nomomicin, etc. The artificial semisynthesis mainly includes amikacin and netilmicin.

Aminoglycoside antibiotics

Aminoglycosides (aminoglycosides) antibiotics are composed of two or three amino sugar molecules and an amino ring alcohol called aglycon, which is a non-sugar moiety, connected by ether bonds, and are divided into two categories: natural and semi-synthetic. Natural sources include those obtained from Streptomyces spp.

Aminoglycoside antibiotics have the following common characteristics:

[Physicochemical properties] Chemical properties are stable, all are alkaline and its salts are easily soluble in water.

This type of antibiotic is a bactericidal drug. The main mechanism of action on bacteria is to inhibit multiple links in the bacterial ribosome cycle, including inhibiting the formation of 70S initiation complexes; selectively binding to target proteins on the 30S subunit to induce mismatches. To synthesize abnormal and non-functional proteins; prevent the stop codon from binding to the ribosome, prevent the synthesized peptide chain from being released, and prevent the 70S ribosome from dissociating, causing the exhaustion of the bacterial core ribosomes, thereby hindering the protein synthesis of bacteria. In addition, it can also attach to the surface of bacteria through ion adsorption, causing cell membrane defects, increased cell membrane permeability, leakage of intracellular potassium ions, nucleotides, enzymes and other important substances, leading to bacterial death.

Because these antibiotics are highly polar compounds and have a low fat solubility, they are not absorbed or seldom absorbed by the oral gastrointestinal tract (<10%), the blood concentration is low, they are only used for gastrointestinal disinfection, and they are often used intramuscularly. And intravenous drip. In addition to this class of antibiotics

Bacteria can show natural and acquired resistance to this class of antibiotics, and bacteria have partial or complete cross-resistance to each other. Drug resistance mainly produces inactivating enzymes mediated by plasmids, which phosphorylate or nucleoside the free hydroxyl groups in their structures and acetylate the free amino groups, thereby losing antibacterial activity. These antibiotics can be inactivated by the same enzyme. The same kind of antibiotics can be inactivated by multiple enzymes. Changes in bacterial cell wall permeability and abnormal intracellular transport functions are also one of the reasons for drug resistance. In addition, mutant strains of Enterococcus bacteria and Mycobacterium tuberculosis

Aminoglycoside antibiotics are mainly used for systemic infections caused by sensitive aerobic gram-negative bacilli. However, severe infection requires

Streptomycin

Broad antibacterial spectrum, it has strong anti-tuberculosis activity. Strong antibacterial effect on most Gram-negative bacteria.

Currently used clinically:

Combined with tetracycline, it is the drug of choice for plague;

It is good for rabbit fever alone;

Combined with tetracycline, it can be used for the treatment of brucellosis;

Used in combination with penicillin to treat infective endocarditis caused by Streptococcus grass and Enterococcus,

Used in combination with ampicillin to prevent sensitive bacterial infections after surgery of the respiratory, gastrointestinal and urinary systems;

Combined with isoniazid and rifampicin, it is used in the initial treatment stage of tuberculosis to delay the occurrence of drug resistance.

Vestibular dysfunction often occurs during streptomycin treatment, and a few patients may develop delayed or progressive auditory nerve damage, hearing loss, or even permanent deafness. Anaphylactic shock can also occur, which usually occurs suddenly within 10 minutes after injection. Although the incidence is less than penicillin, the mortality rate is high. Therefore, a skin test should be performed before injection, and only those who are negative can take the drug. Although the toxicity to the kidney is the lightest among aminoglycosides, those with renal insufficiency should still be used with caution.

Gentamicin

Gentamicin has antibacterial effects on gram-negative bacilli and staphylococcus aureus. It is the main antibacterial agent for the treatment of various gram-negative bacterial infections. It is the first choice among aminoglycosides and is mainly used for:

Combined with broad-spectrum semi-synthetic penicillin or cephalosporin antibiotics for the treatment of severe Gram-negative bacillus infection or mixed infection of Gram-negative bacillus of unknown etiology;

Used in combination with carbenicillin for severe infections caused by Pseudomonas aeruginosa, but the two drugs cannot be infused at the same time, because the latter can reduce the activity of gentamicin;

combined with penicillin or ampicillin or other -lactam antibiotics to treat endocarditis caused by enterococci or Gram-negative bacilli or Pseudomonas aeruginosa;

Combined with metronidazole or chloramphenicol for the treatment of pelvic and abdominal aerobic and anaerobic mixed infections;

Used to prevent postoperative infection before urinary tract and artificial heart valve surgery;

It is used for local infections in ophthalmology, dermatology, ENT, and surgery. However, it can cause photosensitivity reactions. Large-scale application is prone to cause absorption toxicity, so it is rarely used for local application.

Oral can be used for intestinal infections or intestinal preparations.

Adverse reactions include damage to vestibular nerve function, but it is rarer than streptomycin and more common in kidney toxicity.

Tobramycin

The antibacterial effect is similar to that of gentamicin, but the effect of Pseudomonas aeruginosa is 2-5 times stronger than that of gentamicin, and it is still effective for gentamicin-resistant patients. It is mainly used for various severe Gram-negative bacilli infections, but it is generally not the first choice. To Pseudomonas aeruginosa infection or those who need a longer period of medication, tobramycin is appropriate.

Amikacin (amikacin)

It is the most extensive aminoglycoside antibiotic with antibacterial spectrum. Its outstanding advantage is that it is stable to the inactivating enzymes produced by many intestinal gram-negative bacteria and Pseudomonas aeruginosa, so it is resistant to some commonly used aminoglycoside-resistant strains (including aeruginosa Pseudomonas) infection is still effective, is the drug of choice for the treatment of such infections, combined with carbenicillin or ceftiofen, the treatment of neutropenia or other immunodeficiency infections, with satisfactory results. Synergistic with -lactams.

Netilmicin

Its remarkable feature is that it is stable to a variety of amino glycoside inactivating enzymes, and therefore has good antibacterial activity against MRSA and commonly used amino glycoside resistant bacteria. It is clinically used for severe infections caused by sensitive bacteria, but not for non-complex, first-initiated, other safe and effective oral antibacterial drugs that can effectively control urinary tract infections. Its ear and kidney toxicity are low, but do not increase the dose or prolong the course of treatment. If the daily dose & gt; 6 mg / kg or the course of treatment is longer than 15 days, ear and kidney toxicity may occur.