Antimicrobial Agents Essays Example

Essay

Introduction
The choice of antimicrobial agent has a principal meaning for effective treatment of the infections which can be evoked by different causative pathogens. This paper reviews categories of antimicrobial agents, describes the differences between viral and bacterial infections and considers the importance of determining viral or bacterial etiology of the disease for choosing a specific antimicrobial agent.

Summary

All antimicrobials are basically divided into four broad categories: antibacterial, antiviral, antifungal and antiparasitic agents. This classification is based on the type\spectrum of microorganisms these drugs are targeted at, the way of their action and their chemical structure and pharmacokinetics (Archangelo & Peterson, 2013). Antibacterial agents are targeted against bacteria, the single-cell microorganisms lacking nucleus and able to survive without a host (Murray, Kobayashi, Pfaller, & Rosenthal, 1994). Antiviral agents are effective against viruses, or infectious agents comprising a protein coat and RNA\DNA core and requiring a host (living organism) presence to replicate in it. Antifungal drugs’ target is fungi, or eukaryotes with the cell wall structure completely different from that of bacteria. Finally, antiparasitic agents work against parasites, or the species living inside the host, such as protozoae, amoebae, nematodes, cestodes or trematodes. Each of these categories is divided into further sub-categories where different classes of the drugs are distinguished based on their chemical structure and chemical properties.
Viral infections are caused by viruses (size about 20 - 400 nm) which affect the cells metabolic potential, building inside the cell and starting replication process (Archangelo & Peterson, 2013). The fact that viruses’ activity takes place inside the cell makes viral infections less susceptible to treatment as the viruses are not affected by the medicines in the bloodstream. The antiviral agents interfere with certain steps in the viral life cycle or boost the immune response. On the contrary, bacterial infections are caused by bacteria, prokaryotes (size up to 1000 nm) of different shapes (rods, spirals) with complex structure containing lipids, proteins, and peptidoglycans. Bacterial infections are treated by antibiotics, the drugs whose mechanism of actions is inhibition of the bacterias growth or killing the bacteria.The effect of their action is dependent on the concentration of the antibacterial agent in the bloodstream (Murray et al., 1994).
The proper identification of pathogen has a core meaning for the proper treatment. First, it is essential to distinguish between viral and bacterial infections as antimicrobial agents used to treat them have a different way of action. Apart from general mechanism of action, antiviral agents inhibit the virus development at different stages of its life cycle (e.g. inhibiting cell entry, reverse transcriptase, transcription, translation or replication) instead of its destruction or disablement (Arcangelo & Peterson, 2013). They also stimulate the “indirect” virus destruction, when the enhanced immune response (e.g. antibodies synthesis or interferons production) results in the virus attacking by the body‘s immune system (Arcangelo & Peterson, 2013). Antibacterial agents’ action is based on quite the opposite path of the targeted pathogen destruction by inhibiting their cell wall or protein synthesis (penicillines, macrolides), inhibition of nucleic acid\DNA\RNA synthesis (quinolones, rifampicine), and inhibition of cell membrane sterols synthesis (imidazole and other antifungals) or changing the pathways of methabolism inside the cell (isoniazid) (Murray et al., 1994). Each of the agents is highly selective against the corresponding pathogens acting in the way specific to affect a specific microbe, that’s why distinguishing between viral and bacterial infections is crucial. Antibiotics are not effective against viral infections due to the different mechanism of action, and antiviral agents will not destruct bacterias. The knowledge of the causative pathogen has microbiological importance as different antimicrobials have different sites of action and application of the antibiotic to which another pathogen could easily resist by changes in one or couple of amino acids in the strain can lead to easy emergence of the bacteria resistant to this drug. That contributes to the emergence and spread of antimicrobial resistance to the drugs which has become a global health problem (WHO, 2014). The inappropriate use of antimicrobial can increase the number and spread of drug-resistant microbes as well as cause the adverse events in the patients. High frequency of antimicrobials use, when selected inappropriately or applied inconsistently, may increase the frequency of side effects which each antimicrobial agent has. That’s why, apart from distinguising between viral and bacterial infection, it is desirable to precisely define the causative organism to be able to select the most effective antimicrobial treatment. Three essential principles of the antimicrobial agent effectiveness are choosing the agent which is targeted exactly at the pathogen based on susceptibility and resistance, to select the agent with the appropriate activity spectrum (e.g.the narrowest spectrum in periodontal infection, but the widest one in nosocomial pneumonia) and to define the most likely pathogens if it is not possible to diagnoze a specific infection or site of infection (Murray et al., 1994, Becker, 2013). The latter is described as “empiric” method of antimicrobial therapy, different from the specific definition of exact causative organism by the results of clinical cultures (“pathogen-directed” method).

Conclusion

Four categories of antimicrobial agents (antiviral, antibiotics, antifungal and antiparasitic) are applied for the treatment of infections evoked by different types of microorganisms. Viral infections are caused by viruses which cannot exist outside the host, work within the cell and are not reached by the systemic therapy; instead, they are very sensitive to the targeted agents affecting different stages of their life cycle or activating immune response. Bacterial infections are caused by bacteria susceptible to certain classes of drugs (antibiotics) which inhibit their growth or destruct them in different ways (cell membrane, nucleic acid, protein, sterols’ synthesis or metabolism inhibition) and may have both local and systemic effect. Distinguishing between viral and bacterial infections, as well as definition of the specific causative pathogens is vital to choose proper treatment strategy, to prevent antimicrobial drugs resistance and undesirable adverse effects. Defining the specific causative organism allows providing the treatment most beneficial for the patient.

References

Arcangelo, V. P., & Peterson, A. M. (Eds.). (2013). Chapter 8. Principles of Antimicrobial Therapy. In: Pharmacotherapeutics for advanced practice: a practical approach (3rd ed.) (pp. 96–117). Ambler, PA: Lippincott Williams & Wilkins. 
Becker, D. Antimicrobial drugs (2013). Anesth Prog., 60(3), 111–123.
Murray, P. R., Kobayashi, G.S., Pfaller, M.A., and Rosenthal, K. B. (1994). Medical Microbiology. 2nd ed., Mosby, St. Louis.
World Health Organization (2014). Antimicrobial resistance. Retrieved from: http://www.who.int/mediacentre/factsheets/fs194/en/