Introduction to AntibioticsIntroduction to Antibiotics

Prof. Azza ELMedanyProf. Azza ELMedanyPharmacology DepartmentPharmacology Department

Definition of AntibioticsDefinition of Antibiotics

Chemical substances produced by various Chemical substances produced by various microorganisms ( bacteria, fungi, actinomyctes) microorganisms ( bacteria, fungi, actinomyctes) that have the capacity to inhibit or destroy that have the capacity to inhibit or destroy other microorganisms.other microorganisms.

Now a day they are chemically synthesized.Now a day they are chemically synthesized.

They either kill bacteria(bactericidal) or keep They either kill bacteria(bactericidal) or keep more bacteria from growing(bacteristatic).more bacteria from growing(bacteristatic).

Antibiotics will not cure infections caused by Antibiotics will not cure infections caused by viruses.viruses.

CLASSIFICATION OF ANTIBIOTICSCLASSIFICATION OF ANTIBIOTICSACCORDING TO ACCORDING TO MECHANISM OF ACTIONMECHANISM OF ACTION

INHIBITION OF CELL WALLINHIBITION OF CELL WALL SYNTHESIS SYNTHESIS e.g. e.g. Penicillins Penicillins

INHIBITION OFINHIBITION OF PROTEIN PROTEIN SYNTHESISSYNTHESIS e.g.e.g. MacrolidesMacrolides

INHIBITION OF NUCLEIC ACIDINHIBITION OF NUCLEIC ACID SYNTHESIS SYNTHESIS e.g. e.g. Quinolones.Quinolones.

According to spectrumAccording to spectrum

Narrow spectrum , e.g.:Narrow spectrum , e.g.:

penicillin G penicillin G , , aminoglycosidesaminoglycosides

Broad spectrum , e.g.:Broad spectrum , e.g.:

ampicillin ,ampicillin , amoxicillinamoxicillin

Choice of AntibioticChoice of Antibiotic

A)Clinical diagnosisA)Clinical diagnosis (e.g. syphylis)(e.g. syphylis)

B)MicrobiologicalB)Microbiological information information

C)Pharmacological C)Pharmacological consideration consideration

B)Bacteriological informationsB)Bacteriological informations

AdvantagesAdvantages The The exact antibiotic exact antibiotic to be usedto be used The The most effectivemost effective and reject the one and reject the one

with little or no activitywith little or no activity The The least toxicleast toxic The cheapestThe cheapest

DisadvantagesDisadvantages Occasionally these tests do Occasionally these tests do not parallel in vivo not parallel in vivo

sensitivity sensitivity do not take in consideration certain do not take in consideration certain sites of sites of

infectioninfection some bacteria some bacteria cannot be cultivated or take time cannot be cultivated or take time

to grow to grow ( e.g. M. Leprae, M. Tuberculosis )( e.g. M. Leprae, M. Tuberculosis ) Bacteriological Bacteriological services are not available at all services are not available at all

hospitals hospitals

Choice of Antibiotics(cont.)Choice of Antibiotics(cont.)

C)Pharmacological considerationC)Pharmacological consideration 1. Site of1. Site of infection infection 2. Host factors2. Host factors a) a) Immune system Immune system e.g. Alcoholism, diabetes, HIV, e.g. Alcoholism, diabetes, HIV, malnutrition, advanced age- malnutrition, advanced age- ((higher than usual doses or higher than usual doses or longer courses are required ).longer courses are required ).

b) b) Genetic factorsGenetic factors e.g. Patients with G-6-PD deficiency treated with e.g. Patients with G-6-PD deficiency treated with sulfonamides and chloramphenicol sulfonamides and chloramphenicol (Hemolysis ) (Hemolysis )

Choice of Antibiotics ( Cont.)Choice of Antibiotics ( Cont.)

c) c) Pregnancy and LactationPregnancy and Lactation Aminoglycosides- Aminoglycosides- (( hearing losshearing loss)) Tetracyclines- Tetracyclines- ((bone deformity)bone deformity)

d) d) Age of the patientAge of the patient e.g. Grey baby Syndrome- e.g. Grey baby Syndrome- ((chloramphenicol )chloramphenicol )

e) e) Renal function Renal function e.g. Aminoglycosides e.g. Aminoglycosides (( renal failure )renal failure )

f)Liver functionf)Liver function e.g. Erythromycine.g. Erythromycin( hepatic failure( hepatic failure ))

g) g) Poor perfusionPoor perfusion e.g. Lower limbs of diabeticse.g. Lower limbs of diabetics

Choice of Antibiotics ( Cont.)Choice of Antibiotics ( Cont.)

3. Drug Allergy3. Drug Allergy

4. Drug safety4. Drug safety

Chloramphenicol Chloramphenicol (( a plastic anaemia)a plastic anaemia)

Fluoroquinolones in children&Preg. Fluoroquinolones in children&Preg.

(( tendon damage )tendon damage )

5.5. The cost of therapyThe cost of therapy

Bacterial ResistanceBacterial Resistance

Mechanism of Bacterial resistance:Mechanism of Bacterial resistance:

Inactivation of antibiotics by enzymes Inactivation of antibiotics by enzymes produced by bacteriaproduced by bacteriaReduced bacterial permeability to Reduced bacterial permeability to antibiotics antibioticsBacteria develops an altered receptor for Bacteria develops an altered receptor for the drug the drug Bacterial MutationBacterial Mutation

Prevention of ResistancePrevention of Resistance

*Use antibiotics only when absolutely required*Use antibiotics only when absolutely required

*Use antibiotics in adequate dosage for sufficient *Use antibiotics in adequate dosage for sufficient period of time period of time

Not too brief therapyNot too brief therapy

Not too prolonged therapyNot too prolonged therapy

*Combination of antibiotics may be required to *Combination of antibiotics may be required to delay resistance ( e.g. TB ) delay resistance ( e.g. TB )

General Principles of ChemotherapyGeneral Principles of Chemotherapy

Administer drug in Administer drug in full dosefull dose, at , at proper intervalproper interval and by the and by the bbest routeest route

When When apparent cure apparent cure achieved , achieved , continucontinue antibiotic for e antibiotic for about about 3 days 3 days further to avoid further to avoid relapserelapse

Skipping doses Skipping doses may decrease may decrease effectivenesseffectiveness of antibiotic & of antibiotic &

increase the incidence of increase the incidence of bacterial resistance.bacterial resistance.

General Principles of Chemotherapy(cont.)General Principles of Chemotherapy(cont.)

Indications for antibiotic combinationsIndications for antibiotic combinations: : Mixed bacterial infectionsMixed bacterial infections Ill patient of unknown etiologyIll patient of unknown etiology Prevent emergence of resistance Prevent emergence of resistance Achieve synergismAchieve synergism Disadvantages of multiple antibioticsDisadvantages of multiple antibiotics Increased risk of sensitivity or toxicityIncreased risk of sensitivity or toxicity Increased risk of bacterial resistant Increased risk of bacterial resistant Possibility of antagonismPossibility of antagonism Higher costHigher cost

General principles ( Cont. )General principles ( Cont. )

In some infections bacteriological proof of cure isIn some infections bacteriological proof of cure is required .required .

Measurement of plasma conc. of antibiotics is seldomMeasurement of plasma conc. of antibiotics is seldom needed.needed.

Indications for antibiotics Indications for antibiotics prophylaxisprophylaxis

Surgical prophylaxisSurgical prophylaxis bowel surgery, joint replacement, and some gynecological interventionsbowel surgery, joint replacement, and some gynecological interventions to prevent postoperative infections. to prevent postoperative infections.

Immunosuppressed PatientsImmunosuppressed Patients Very old, very young Very old, very young Diabetics, …… Diabetics, ……

Dental extractionsDental extractions Pts with total joint replacementsPts with total joint replacements Pts with cardiac abnormalitiesPts with cardiac abnormalities

MISUSES OF ANTIBIOTICSMISUSES OF ANTIBIOTICS

Wrong diagnosisWrong diagnosis e.g. viral infectionse.g. viral infections Improper dosageImproper dosage.. Therapy of fever of unknown origin.Therapy of fever of unknown origin. Presence of pus or necrotic tissues , or blood Presence of pus or necrotic tissues , or blood

at the surgical site at the surgical site Excessive use of prophylactic antibiotics Excessive use of prophylactic antibiotics Lack of adequate bacteriological Lack of adequate bacteriological

information. information.