This document outlines the principles of antibiotic therapy, including determining when antibiotic treatment is necessary based on the presence of infection and state of the patient's defenses. It discusses choosing the appropriate antibiotic based on identifying the causative organism and determining antibiotic sensitivity. Broad-spectrum antibiotics are not preferred, and narrow-spectrum antibiotics with a proven history of effectiveness against the identified bacteria are recommended. Proper dosing, timing, route of administration, and use of combination therapy are also important principles for antibiotic administration and treatment.

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Principles of Anti-biotic
Therapy
By: Prof. Ahmed M. El-Sabbagh
The principles of anti – biotic use
* Therapeutic * Prophylactic
The guideline in making a decision to give
an anti-biotic:
1. Presence of infection, how ?
a. Locally, the presence of classic signs and symptoms
b. Systemically, the presence of fever, lymphadenopathy ,
malaise, a toxic appearance, and an elevated white blood cell count.
II. State of host defenses
Evaluation of the general state of the host defense mechanism
Causes of depressed defenses are
1. Physiologic
2. Disease – related
3. Defective immune system – related
4. Drug suppression – related :
a. Cytotoxic drugs
b. Immunosuppressive drugs ( Steroids )
III. Incision and Surgical drainage
The purpose of this procedure is to release the pressure
that has built up in the tissue , thereby increasing the
vascular flow.
This can be accomplished by nerve exacerbation, tooth
extraction or surgical incision.
IV. The decision to use antibiotic therapy
Since the host is responsible for curing the infection.
therefore, minor or even moderately severe infections in
patient with intact host defenses may not require
antibiotic therapy.
Principles For Choosing The
Appropriate Anti-biotic
I. Identification of the causative organism
The pathogen is determined either
a. in the laboratory
b. based upon knowledge of
the pathogenesis and
clinical presentation of specific infections.
Antibiotic will then be either initial or definitive, depending
upon whether or not the organism is diagnosed
Facts regarding the type of bacteria and their
specific identification in odontogenic infections
1. About 70 % of the infections are caused by mixed
types of bacteria ( aerobic & anaerobic )
infections caused by only aerobes are much less
common ( 5 % ) , while pure anaerobes are 25 % .
2. The isolated bacterium in majority of cultures is
Streptococcus, accounting for up to 95% of aerobes.

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3. The anaerobic population is distributed among a
large variety of bacteria, the most common are:
i. Streptococcus intermedius
ii. Peptostreptococcus
iii. Peptococcus
iv. Bacteroids
v. Fusobacterium
The type and mix of bacteria is vary with the stage of
infection.
In the early cellulitis stage of infection, the aerobic
bacteria dominate.
As the reduction – oxidation potential in the area of
infection is changes, anaerobic bacteria become
increasing.
By the time the infection reaches a chronic abscess
stage, anaerobic bacteria become the only type.
These facts have major clinical importance:
The antibiotic that is useful for odontogenic infections
must be effective against Streptococcus and against
anaerobes.
So clinically, In the early stage of odontogenic infection,
anti-streptococcal activity is more important .
In the later stage, chronic abscess situation, anti –
anaerobic activity is the major antibiotic goal.
Routine culture of mild and moderate odontogenic
infections are not necessary. But , at the time of surgical
treatment, a smear of pus should be made for future Gram
stain.
Indications for obtaining CULTURES !
1. Compromised host defenses
2. Patient has received treatment for three days without
improvement
3. Post-operative wound infection
4. A recurrent infection
5. Osteomylitis
Principles For Choosing The Appropriate Anti-biotic
II. Determination of the Anti – biotic Sensitivity
When treating an infection that has not responded to initial antibiotic
therapy,
or
When treating a post-operative wound infection,
The causative agent must be identified , and
The antibiotic sensitivity must also be determined
Most odontogenic infections are caused by Streptococci, but a few
others are caused by organisms of unexpected resistance and
sensitivity as Staph.
Penicillin G has been the drug of choice in past years, but
because of the predominance of penicillinase – producing strains, it
can only be used if sensitivity studies support it.
Instead, penicillinase – resistant penicillins should be used.
Penicillin is excellent for streptococcus,
and is very good to excellent for the major anaerobes of
odontogenic infections.
Erythromycin is very effective against Streptococcus, and
Peptostreptococcus, but is ineffective against Peptococcus and
Fusobacterium.

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Clindamycin is very good for Streptococcus and for the five major
anaerobic groups.
Cephalexin is only moderately active against Streptococcus ( about
10 % of strains are resistant, 70 % are intermediately sensitive, and
20 % are sensitive ) , and is good to very good against the five groups
of anaerobes.
Metronidazole has no activity against Streptococcus but has
excellent activity against the five anaerobic groups.
Criteria for Selection of Antibiotic
1. Use of a specific narrow spectrum antibiotic
The use of broad spectrum antibiotic will lead to
development of resistant strains, and many different
bacteria present in the body will also exposed to the
antibiotic.
however, if a narrow spectrum antibiotic is used, fewer
organisms have the opportunity to become resistant,
and it will also minimizes the risk of superinfections.
Criteria for Selection of Antibiotic
2. Use of the least toxic antibiotic
Antibiotics are utilized to kill living bacteria, but some
antibiotics also kill or injure human cells.
3. Patient's drug history
4. Use of bactericidal rather than bacteriostatic drug
5. Use of antibiotic with a proven history of success
6. Cost of the antibiotic
Criteria for Selection of Antibiotic
Principles of Antibiotic Administration
1. Proper Dose
* MIC of the drug * Avoid subtherapeutic level
2. Proper Time Interval
* Plasma half-life (T1/2 )
3. Proper Route of Administration
4. Consistency to Route of Administration
5. Combination Antibiotic Therapy
PROPHYLACTIC ANTIBIOTICS
Advantages
1.Prevention of infection
2. Decreased patient morbidity
3. Decreased patient mortality
4.Decreased hospital stay
5. Decreased medical cost
6. Decreased total antibiotic usage
7. Decreased numbers of resistant bacteria

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PROPHYLACTIC ANTIBIOTICS
Disadvantages
1. No reduction of infection
2. Development of increased numbers of resistant
bacteria
3. Delay in onset of infection
4. Adverse effect on surgical technique
Principles for the use of Prophylactic Antibiotics
1. High risk of infection
2. Causative organism must be know
3. Antibiotic susceptibility must be known
4. Appropriate Timing
5. High-Dose Antibiotic
Specific Indications For Antibiotics
Penicillin Streptococcus
Dicloxacillin (Penicillinase-resistant penicillin) Staphylococcus
Erythromycin (Bacteriostatic + used in low doses )
Clindamycin used in chronic osteomylitis
Amoxicillin little indicated in odontogenic infection
Cephalosporins broad-spectrum, bactericidal
Tetracyclines effective against anaerobic flora ( for
periodontal disease)
Metronidazole bactericidal against anaerobes
Nystatin for mucosal candidiasis
Imipenem it is a ß - lactam