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Antimicrobials
Antimicrobials are chemicals that are used in the treatment of infectious diseases.
Most microbiologists distinguish two groups of antimicrobial agents used in the treatment of infectious
disease: antibiotics, which are natural substances produced by certain groups of microorganisms, and
chemotherapeutic agents, which are chemically synthesized. A hybrid substance is a semi-synthetic
antibiotic, where a molecular version produced by the microbe is subsequently modified by the chemist to
achieve desired properties.
The modern area of antimicrobial chemotherapy began in 1929 with Fleming's discovery of the powerful
bactericidal substance penicillin, and Domagk's discovery in 1935 of synthetic chemicals (sulfonamides) with
broad antimicrobial activity.
In the early 1940's, spurred partially by the need for antibacterial agents in WWII, penicillin was isolated,
purified and injected into experimental animals, where it was found to not only cure infections but also to
possess incredibly low toxicity for the animals. The rapid isolation of streptomycin, chloramphenicol and
tetracycline soon followed, and by the 1950's, these and several other antibiotics were in clinical use.
The most important property of an antimicrobial agent, from a host point of view, is its selective toxicity, i.
e., the agent acts by inhibiting or killing bacterial pathogens but has little or no toxic effect on the host.
This implies that the biochemical processes in the bacteria are in some way different from those in the
animal cells, and that the advantage of this difference can be taken in chemotherapy.
Characteristics of Antibiotics -
Antibiotics are low-molecular weight substances that are produced as secondary metabolites by certain groups
of microorganisms, especially Streptomyces, Bacillus, and a few molds (Penicillium and Cephalosporium) that
are inhabitants of soils.
Antibiotics may have a cidal (killing) effect or a static (inhibitory) effect on a range of microbes. The range
of bacteria or other microorganisms that are affected by a certain antibiotic are is expressed as its spectrum
of action. Antibiotics effective against procaryotes, which kill or inhibit a wide range of Gram-positive and
Gram-negative bacteria, are said to be broad spectrum. If effective mainly against Gram-positive or Gram-
negative bacteria, they are narrow spectrum. If effective against a single organism or disease, they are
referred to as limited spectrum.
Desirable properties of a clinically useful antibiotic are as the following:
-It should have a wide spectrum of activity with the ability to destroy or inhibit many different species of
pathogenic organisms.
-It should be nontoxic to the host and without undesirable side effects.
-It should be non allergenic to the host.
-It should not eliminate the normal flora of the host.
-It should be able to reach the part of the human body where the infection is occurring.
-It should be inexpensive and easy to produce.
-It should be chemically stable.
-Low resistance by microbes.
Objective from an antibiotic:
To have proper concentration of specific antibiotic at the site of infection, which is good enough to kill the
microorganism, without harming the host?
* To select Antibiotic we have to consider the following:
1- Causative Microorganism
a Clinical picture of the host (symptoms).
b Bacteriological examination (culture).
2- Pharmacokinetic factors.
a Site of infection and tissue penetration.
e.g. if the drug penetrates Blood Brain Barrier ;BBB, (or the meninges) the drug could be used for Central
Nervous System (CNS) infections such as meningitis.
b Renal disease; in the case of renal infections the drug should be secreted unchanged via kidneys, on
the contrary in the case of renal function compromised patient the drug shouldn’t be given only if the dose is
adjusted.
c Liver disease, i.e. dose should be adjusted in hepatic disease conditions, if the drug is metabolized
extensively in the liver.
d Route of administration (if there is vomiting PO rout is avoided).
3- Host factors:
a Host defense mechanism (immune system, phagocytosis) .
b Local factors at the site of infection.
c Age.
d Genetic factors; “like patients who have G6PD deficiency ; develop sever side effect
in response to some antibiotic”
e Pregnancy especially in the first trimester .
f Breast feeding: you the secretion of the antibiotic in breast milk should be taken in consideration
whether it is safe regarding the neonate, or it has low concentration secreted.
g Drug Allergy: e.g. Penicillin allergy which is very important to know before giving such a drug.
Antimicrobials are chemicals that are used in the treatment of infectious diseases.
Most microbiologists distinguish two groups of antimicrobial agents used in the treatment of infectious
disease: antibiotics, which are natural substances produced by certain groups of microorganisms, and
chemotherapeutic agents, which are chemically synthesized. A hybrid substance is a semi-synthetic
antibiotic, where a molecular version produced by the microbe is subsequently modified by the chemist to
achieve desired properties.
The modern area of antimicrobial chemotherapy began in 1929 with Fleming's discovery of the powerful
bactericidal substance penicillin, and Domagk's discovery in 1935 of synthetic chemicals (sulfonamides) with
broad antimicrobial activity.
In the early 1940's, spurred partially by the need for antibacterial agents in WWII, penicillin was isolated,
purified and injected into experimental animals, where it was found to not only cure infections but also to
possess incredibly low toxicity for the animals. The rapid isolation of streptomycin, chloramphenicol and
tetracycline soon followed, and by the 1950's, these and several other antibiotics were in clinical use.
The most important property of an antimicrobial agent, from a host point of view, is its selective toxicity, i.
e., the agent acts by inhibiting or killing bacterial pathogens but has little or no toxic effect on the host.
This implies that the biochemical processes in the bacteria are in some way different from those in the
animal cells, and that the advantage of this difference can be taken in chemotherapy.
Characteristics of Antibiotics -
Antibiotics are low-molecular weight substances that are produced as secondary metabolites by certain groups
of microorganisms, especially Streptomyces, Bacillus, and a few molds (Penicillium and Cephalosporium) that
are inhabitants of soils.
Antibiotics may have a cidal (killing) effect or a static (inhibitory) effect on a range of microbes. The range
of bacteria or other microorganisms that are affected by a certain antibiotic are is expressed as its spectrum
of action. Antibiotics effective against procaryotes, which kill or inhibit a wide range of Gram-positive and
Gram-negative bacteria, are said to be broad spectrum. If effective mainly against Gram-positive or Gram-
negative bacteria, they are narrow spectrum. If effective against a single organism or disease, they are
referred to as limited spectrum.
Desirable properties of a clinically useful antibiotic are as the following:
-It should have a wide spectrum of activity with the ability to destroy or inhibit many different species of
pathogenic organisms.
-It should be nontoxic to the host and without undesirable side effects.
-It should be non allergenic to the host.
-It should not eliminate the normal flora of the host.
-It should be able to reach the part of the human body where the infection is occurring.
-It should be inexpensive and easy to produce.
-It should be chemically stable.
-Low resistance by microbes.
Objective from an antibiotic:
To have proper concentration of specific antibiotic at the site of infection, which is good enough to kill the
microorganism, without harming the host?
* To select Antibiotic we have to consider the following:
1- Causative Microorganism
a Clinical picture of the host (symptoms).
b Bacteriological examination (culture).
2- Pharmacokinetic factors.
a Site of infection and tissue penetration.
e.g. if the drug penetrates Blood Brain Barrier ;BBB, (or the meninges) the drug could be used for Central
Nervous System (CNS) infections such as meningitis.
b Renal disease; in the case of renal infections the drug should be secreted unchanged via kidneys, on
the contrary in the case of renal function compromised patient the drug shouldn’t be given only if the dose is
adjusted.
c Liver disease, i.e. dose should be adjusted in hepatic disease conditions, if the drug is metabolized
extensively in the liver.
d Route of administration (if there is vomiting PO rout is avoided).
3- Host factors:
a Host defense mechanism (immune system, phagocytosis) .
b Local factors at the site of infection.
c Age.
d Genetic factors; “like patients who have G6PD deficiency ; develop sever side effect
in response to some antibiotic”
e Pregnancy especially in the first trimester .
f Breast feeding: you the secretion of the antibiotic in breast milk should be taken in consideration
whether it is safe regarding the neonate, or it has low concentration secreted.
g Drug Allergy: e.g. Penicillin allergy which is very important to know before giving such a drug.