ANTIMICROBIAL AGENTS

Antimicrobial agents are chemical substances such as antiseptics, disinfectants or
antibiotics that kill and supress microorganisms’ growth. Antimicrobial drugs are effective in
treating infections due to their selective toxicity. They have the ability to kill or injure an
invading microorganism without any harm to the host’s cells (Nimavat, Joshi, & Jani, 2014).
Dose and optimal time for microbial therapy is determined by patient factors such as weight,
age and concurrent diseases. Before any antibiotic therapy, a systematic approach that
identifies the site and source of infection must be taken.
Antimicrobial agents are roughly divided in two: bacteriostatic (they slow the growth
of bacteria) and bactericidal (they actively kill bacteria), but there is overlapping on
individual agents and doses used. Most antimicrobial agents are bactericidal including
cephalosporins, fluoroquinollines, aminoglycosides, vancomycin, daptomycin, and
metronidazole. Notable exceptions to this are trimethoprim, macrolides, sulphonamides, and
tetracyclines, all of which are bacteriostatic. It may be rational to favour bactericidal agents
over bacteriostatic agents none is superior to the other.
Pharmcodynamics is a complex discipline but most antimicrobial agents efficacy, can
be categorised as either concentration-dependent or time-dependent. Concentration-
dependent agents’ clinical efficacy, for example, aminoglycosides and fluoroquinolones, is
dependent on either the area under the serum concentration curve, the peak serum
concentration, or both. Time-dependent agents’ clinical efficacy, (for example, penicillin,
vancomycin, cephalosporins, carbapenems, macrolines, and clindamycin) (Nimavat, Joshi, &
Jani, 2014), are in contrast, only dependent on the time which is above MIC exert their
bactericidal and those which are bacteriostatic.

ANTIMICROBIAL AGENTS 3

3
Penicillins- the mechanism of action of penicillin, cell wall synthesis is inhibited by
β-lactam ring through inhibiting the third and final step in formation of peptidoglycan and
binding penicillin-binding proteins (PBPs). PBS is on inner membrane of Gram negatives and
on the outer membrane of Gram positive. Penicillin’s efficacy is related to the percentage of
time which is the minimum inhibitory concentration (MIC). On the β-lactam rings,
carbapenems are the fastest while cephalosporins are the slowest. Penicillinase-resistant
PCNs (nafcillin) have lost ground to the MRSA, while extended-spectrum PCNs (ticarcillin,
piperacillin, and ampicillin) cover GNBs.
Cephalosporins Mechanism of Action, cell wall synthesis is inhibited by β-lactam
ring by inhibiting the third and final step in formation of peptidoglycan and binding
penicillin-binding proteins (PBPs). Its efficacy is related to percent of time above the
minimum inhibitory concentration (MIC). Among all the β-lactams, they are the slowest in
contrast with carbapenems, kill the fastest, and are clearly synergistic with aminoglycosides
and dyssyngergistic with fluoroquinolones (2012).
Many human infections are caused by either viruses or bacteria (Donbavand &
Chernett, 2012). Bacteria are single celled microorganism thriving in different environments.
Some bacteria are beneficial like the gut bacteria which helps in digestion while others are
responsible for infections and are known as pathogenic bacteria. Examples of infections
caused by bacteria include tuberculosis, strep throat, and urinary tract infections. Viruses are
smaller in size as compared to bacteria and require a living host to multiply like animals,
people, or plants causing diseases like common cold, AIDS, and chickenpox.
For pathogenic bacteria to cause diseases, they must gain access into the body. The
access routes of bacteria in the body include contaminated water or food, cuts, touching
contaminated surfaces, contact with an infected person and breathing infected droplets.

ANTIMICROBIAL AGENTS 4

4
According to Donbavand & Chernett (2012), viruses are spread from one person to another
through vomit, sneezes, cough, exposure to infected fluid, and bites from infected insects and
animals. Bacteria are alive and do not invade host cells for them to replicate which is in
contrary to virus that require a cell in order to invade the host. Bacteria may take up nutrients
from a tissue, replicate inside the host cell, or secrete toxins that kill the host cells (Gilbert,
2013). This, unlike viruses which require a host cell, hijacks the host cell machinery causing
it to replicate. The host cell becomes a slave to the virus, multiplies and later bursts to invade
the tissues. Bacterial infections are treated and managed by antibiotics, in case of viral
infection, antibiotics are useless in treatment. This is because viruses use their host cells in
performing their activities and antivirus which perform differently from antibiotics are used
as they interfere with viral enzyme. Medical intervention is required to differentiate between
viral infection and bacterial infection as both cause fever and irritability.
Selecting an antibiotic that is effective against a specific pathogen is a very important
task for every health provider. It is critical to isolate specific pathogens in many life
threatening, serious infections especially in situation requiring prolonged therapy (De Filippis
& McKee, 2013). Incorrect drug selection delays proper treatment by giving the said
microorganism more invading time. Ineffective antibiotics will promote resistance which
may lead to adverse effects on a patient. It is ideal to conduct a laboratory test to identify
specific pathogen before beginning an anti-infective therapy.
In ensuring accurate microbiological diagnosis, physicians should ensure all
diagnostic specimens are obtained properly and submitted promptly to the microbiology
laboratory (Nimavat, Joshi, & Jani, 2014). It is an advantage to identify a causative pathogen
as it allows optimal antibiotic selection and the outcome of the patient. Specimens should be
correctly and accurately collected, taken to the microbiology lab while ensuring no
contamination. Contamination especially between two specimens may lead to misdiagnosis.

ANTIMICROBIAL AGENTS 5

5
Due to their widespread familiarity and availability, relative cost and general low cost; they
are among the most misused drugs (De Filippis & McKee, 2013).
Several factors are to be considered before selecting an antimicrobial regime. Before
initiating any antibiotics, every attempt should be made to get specimens for sensitivity and
cultures testing. In case of delayed dermatologic reactions (i.e., rash) to penicillin, they
should be given cephalosporins as an option, also, patients with anaphylaxis or type I
hypersensitivity reactions to penicillins should not receive cephalosporins (2012).
Alternatives to the cephalosporins include quinolones, sulfonamide, antibiotics, vancomycin,
or aztreonam based on type of coverage indicated. Estimated creatinine clearance must be
calculated for every client who is to receive antibiotics and while adjusting the interval of the
antibiotic dose accordingly (Arcangelo & Peterson, 2013).
Nutritional supplements and all concomitant drugs should be reviewed when an
adding antibiotic to a patient’s therapy to avoid drug–drug interactions. According to
Arcangelo & Peterson (2013), indication should consist of combination antibiotic therapy for
polymicrobial infections (gynecologic infections, intra-abdominal), in producing synergistic
killing (such as aminoglycoside versus Pseudomonas aeruginosa plus β-lactam), or to
prevent the emergence of resistance. Patients not responding to an appropriate antibiotic
therapy within 2 to 3 days should be re-evaluated (Gilbert, 2013). This will ensure; that
therapeutic drug concentrations are being achieved, the correct diagnosis, that the patient is
not immunosuppressed, that resistance has not developed or that the patient does not have
isolated infection (such as abscess, foreign body). All antibiotic receiving patients should be
monitored for resolution of infectious symptoms and signs (e.g., decreasing white blood cell
count and reduced temperature) and adverse drug events.

ANTIMICROBIAL AGENTS 6

6
Drug-resistant microorganisms have emerged to be a major problem around the
world. Today, the adverse impact of resistance is not limited to bacterial realm, viruses and
even fungi are becoming resistant. In chemotherapy to treat viral disease like human
immunodeficiency virus (HIV), resistance has become a major problem (Arcangelo &
Peterson, 2013). After the pharmacodynamically linked variable delineation, it is possible to
generate dosing regimens that lower the resistance probability with existing circumstances
where combination therapy may be required (for example tuberculosis and HIV therapy)
(Nimavat, Joshi, & Jani, 2014). There is a rising need to lower the resistance probability and
maintain the utility of the drugs that are currently in the therapeutic armamentarium.
Carbapenems are part of prevention model compounds in resistance because they very
infrequently allowing resistance among gram-negative isolate to emerge. Fluoroquinolones
are also excellent candidates in suppressing resistant mutants by giving attention to dosing.
Organisms become resistant to the class of agents through either alone or in combination
(Arcangelo & Peterson, 2013). Resistance in HIV differs in kind from those among bacteria.
The major difference revolves around the therapy duration with majority of bacterial
infections, with most often stopping between 7 and 14 days, the course of therapy is limited
which is in contrast to HIV therapy which take a long life.
Conclusion

Antimicrobial agents are seen to transform the modern world. Diseases that
previously caused morbidity and mortality on a large scale are brought under control.
Although the therapy of infective pathogens is successful, emergence of resistance is
threatening this success. Consequently, it is sensible to prescribe doses of available
therapeutic agents, that will maximize the therapy probability that will not only produce a
high likelihood of success with a low toxicity likelihood, but will also diminish the

ANTIMICROBIAL AGENTS 7

7
probability that clone resistant will become the population dominant while under the pressure
of the agents or therapeutic agent. With combination therapy, it is essential to model the way
drugs act in combination (, additively, antagonistically or synergistically) and how the
differing population pharmacokinetics affects the outcome. Through this, there is a possibility
to maintain the drug utility that is already in therapeutic armamentarium.

ANTIMICROBIAL AGENTS 8

8

References

(2012). Drug.com. Retrieved 30 May 2016, from http://www.drugs.com /
Arcangelo, V. & Peterson, A. (2013). Pharmacotherapeutics for advanced practice.
Philadelphia, PA: Lippincott Williams & Wilkins.
De Filippis, I. & McKee, M. (2013). Molecular typing in bacterial infections. New York:
Springer.
Donbavand, T. & Chernett, D. (2012). Virus. Edinburgh: Barrington Stoke.
Gilbert, D. (2013). The Sanford guide to antimicrobial therapy. Sperryville, Va.:
Antimicrobial Therapy.
Nimavat, K., Joshi, K., & Jani, G. (2014). Antimicrobial Agents. Saarbrücken: Lap Lambert
Academic Publishing.