Chemotherapeutic antibacterial drugs

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Antimicrobials are different chemical compounds that kill (microbicidal action) or suppress the growth or replication of pathogenic or non-pathogenic microorganisms such as bacteria, fungi and protozoans. The history of antimicrobial preparations traces back in the beginning of 19th century when Louis Pasteur observed that some of microorganisms may suppress the growth and development of other microorganisms. He found that an airbone bacillus can inhibit the growth of Bacillus anthracis. Lately this phenomen was called antibiosis. Antibiosis is a biological interaction between two or more organisms and is usually characterized by antogonism of one organism and the metabolic substances produced by another microorganism. In 1942 year the substances produced by certain microorganism which kill or suppress the growth of another microorganisms were called antibiotics by an American microbiologist Selman Waksman. Currently, the term antibiotic refers to any medical preparations that is used to treat bacterial infection.

Antibiotics are the most commonly used and prescribed preparations among all antimicrobial medications. They are indicated in the treatment of infections caused by sensitive microbicidal as mononotherapy or in combination with other medical preparation. In appropriate use antibiotics are considered to be effective and safe remedies in the treatment of bacterial infections. However, is spite of this fact the use of many antibiotics is limited due to increasing the resistance of the majority microorganisms as well as many adverse effects common for many antibiotics. For example, the use of flourquinolones is contraindicated in patients under 18 years because of high risk of tendon damage; aminoglycosides possess ototoxicity and nephrotoxicity and may cause severe adverse effects; many beta-lactam antibiotics may change stomach and intestinal microflora causing pseudomembranous colitis.

A huge variety of antibiotics, the difference in their chemical structure and action mechanism became the reason for their classification and dividing into several groups. In dependence on action on microbial cells antibiotics are classified into the following groups:

  • Bacteriostatic (suppression of bacterial growth and replication)
  • Bactericidal (lysis of microorganisms associated with damage of bacterial cell wall)

According to chemical structure, antibiotics are divided into the following groups:
Beta-lactam antibiotics which are subdivided into 4 subgroups:

  • Penicillins is a group of antibiotics derived from Penicillium fungi. Penicillin antibiotics are historically significant because they were the first effective medicines against many previously serious diseases such as syphilis and Staphylococcus infections.
  • Cephalosporins have a similar structure with penicillins. Cephalosporins include a wide variety of antibiotics divided into 5 generations. Cephalosporins are the most widely used medications in clinical practice.
  • Carbapenems belong to beta-lactams. They are characterized by a high resistance to hydrolysis of beta-lactamases and possess a broad spectrum of antibacterial activity. In most cases they are considered to be preparations of reserve.
  • Monobactams are preparations with a narrow spectrum of antibacterial activity. Monobactams are indicated for the treatment of infections caused by aerobic gram-negative microorganisms
  • Macrolides are antibiotics with a complex cyclic structure. They exert bacteriostatic action. Macrolides are divided into 14-, 15-, and 16-membered. Macrolides are indicated for the treatment gram-positive cocci and intracellular pathogens (mycoplasma, chlamydias). They are considered to be less toxic antibiotics.

Tetracycline are one of the first group of antibiotics. They are used to treat infections of the respiratory and urinary tract, treatment of severe infections such as anthrax, tularemia, brucellosis. They exert bacteriostatic action.

Aminoglycosides are considered to be the most toxic antibiotics. They are used in the treatment of nosocomial infections caused by gram-negative pathogens and infectious endocarditis. Aminoglycosides possess potential nephro-, and ototoxicity and may cause neuromuscular block.

Quinolones and fluorquinolones. Fluorquinolones were approved for clinical use at the beginning of 1980-years. They are characterized by a broad spectrum of antibacterial action including staphylococci, bactericidal activity and good pharmakoninetic characteristics.

Lincosamides include natural and semi-synthetic antibiotics that possess a narrow spectrum of action. They are used to treat infections caused by gram-positive cocci.

Glycopeptides are used in clinical practice since 1960 years. They are used in the treatment of nosocomial infections caused by gram-positive microorganisms. They are also indicated for the treatment of MRSA, MRSE, and enterococcal infections.

Polymixins is one of the first group of antibacterial preparations. They are characterized by a narrow spectrum of activity and high toxicity.

Oxazolidines. Oxazolidines are up-to-date group of antibiotics. They are used in the therapy in the therapy of infections caused by polyresistant gram-positive cocci.

Nitrofurans is the group of antibacterial preparation that is initially used in the treatment of urinary tract infections.

Nitroimidazoles are synthetic antibacterial drugs with high activity against anaerobic bacteria and protozoans.