PRINCIPLES OF ANTIMICROBIAL THERAPY

INDRATI

Antimicrobial drugs are effective in treatment of infections because of their selective toxicity

Source of infection are : bacteria, fungi, virusAntibiotic is a substance to inhibit or kill bacterialAntisepsis is the use of chemicals to destroy most

pathogenic organism on animate surface -- antiseptics

Disinfection is the application of chemicals to destroy most pathogenic organism on inanimate surfaces disinfectants

Antifungal is a substance to inhibit fungalAntivirus is a substance to inhibit viral

Selection of AM agent Required knowledge of :1. Identification & sensitivity of the organism2. Site of action : adequate level of AM in SOI3. Safety the agent4. Patient factors : age, pregnancy, renal &

hepar dysfunction, immune system5. Cost of therapy

Mechanisms of action :1. Inhibition of cell wall synthesis : penicillin,

cephalosporin, vancomycin2. Alteration of cell membranes integrity :

amphotericin B, azoles, nystatin3. Inhibition of ribosomal protein synthesis :

clindamycin, macrolides, tetracyclines4. Suppression of DNA : metronidazole5. Inhibition of folic acid synthesis :

sulfonamides

Drug resistance- Microbial growth is not halted by the maximal

level of AM that is tolerated by the host- Some organisms inherently resisten to an AM e.g Gram – resistent to eritromycin- Microbial species normally responsive to

particularly drug, may developed resistent strains

Mechanism of drug resistance - Genetic alteration : spontaneus mutations of

DNA- Enzymatic inactivation

Antimicrobial drugs are classified as either bacteriostatic or bactericidal. Bacteriostatic arrest the growth and replication. Bactericidal, organism are killed byAM

Antimicrobial drugs spectra :- Narrow spectrum : acting only on a

single/limited group of microorganism- Broad spectrum : affect a wide variety of

microbial

Clinical indication of AM combination- Mixed infection- Synergism effect- Risk of developing resistent organisms- Increase antimirobial coverage- Infection of unknown origin

Some clinical situation for prophylactic AM- pre-dental extraction who have implanted

prosthetic devices- Pre-operative treatment (e.g bowel- Protect fetus in HIV infection pregnant woman

Side effect of AM therapy :Hypersensitivity: allergic & idiosyncracyDirect toxicity: ototoxicSuper infection

Antibiotic failure :- Incorrect diagnosis- Antibiotic antagonism- Delay in diagnosis- Inability of the antibiotic to penetrate to the site

of infection- To low a blood antibiotic concentration- Failure to surgically eradicate the source of the

infection- Inadequate host defenses- Inappropriate choice of antibiotic- Emergence of antibiotic resistance

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