1. PRINCIPLES OF ANTIMICROBIAL THERAPY

2. ANTIMICROBIAL THERAPY TAKES ADVANTAGE OF BIOCHEMICAL DIFFERENCES BETWEEN MICRO ORGANISMS AND HUMANS.
SELECTIVE TOXICITY
RELATIVE RATHER THAN ABSOLUTE.

3. PRINCIPLES OF ANTIMICROBIAL THERAPY
SELECTION OF ANTIMICROBIAL AGENT
Identity of organism & its sensitivity
Site of infection
Safety of agent
Patient factors
Cost of therapy

4. Identity of organism
Obtain sample prior to starting therapy
Microsopic examination
Gram stain
Culture media
sensitivity

5. Site of infection
The blood brain barrier
Choose drugs which are more lipid soluble
Low degree of protein binding
Low molecular weight

6. Safety of the agent
Penicillins are among the least toxic of the antibiotics
Drugs such as chloramphenicol are reserved for severe resistant cases

7. Patient factors
All conditions which can ,< immune function have to be looked for
Alcoholism, DM, malnutrition, advanced age, HIV.
Renal function– drugs which are nephrotoxic are to be avoided
Pregnancy
Lactation
Drugs like tetracyclines, aminoglycosides are to be avoided.
Age new born –avoid chloramphenicol , infants-- tetracycline

8. Emperic therapy prior to organism identification Acutely ill patient
Identification & sensitivity of organism
Selection of drug --
Status of the patient- renal, hepatic.
Pregnancy & lactation, age -

9. -Bacteriostatic -Bactericidal Spectrum Narrow spectrum-- Isoniazid Extended spectrum-- ampicillin Broad spectrum– tetracycline, chloramphenicol

10. Minimum inhibitory concentration (MIC)
LOWEST concentration of the antibiotic which inhibits growth
To provide effective antimicrobial therapy the antibiotic concentration should be more than MIC

11. Minimum bactericidal concentration
Lowest concentration of antimicrobial agent that results in a percent decline in colony count.

12. Combination of drugs used in
Mixed infections
Unknown origin
Resistant organisms
Better to use bacteriostatic with bacteriostatic, or bactericidal with bactericidal!

13. Synergism between the actions of two or more drugs.
Two bactericidal agents: Use a penicillin and an aminoglycoside. The increase in cell-wall permeability caused by the penicillin allows for easier access of the aminoglycoside.
To delay development of resistance.
For the treatment of "mixed" infections.

14. Drug resistance
Mainly by Mutations of DNA DNA transfer of drug resistance Modification of target sites Decreased accumulation Enzymic inactivation

17. Complications of antibiotic therapy
Hypersensitivity--- penicillin-urticaria, anaph shok
Direct toxicity---- aminoglycoside
Super infections
SUPERINFECTIONS: Oral, GU, and GI superinfections can occur with use of antibiotics. GI infections are most common.
Intestinal Candidiasis: Fungal overgrowth of the Candida secondary to giving an oral antibiotic and depleting intestinal flora. Add an antifungal drug to treat it.

18. Staphylococcal Enterocolitis: Life-threatening infection with Staph Aureus as a result of antibiotics. To treat it:
Stop the original antibiotic therapy.
Start therapy with vancomycin or some other appropriate agent to fight Staph Aureus.
Pseudomembranous Colitis: Life-threatening infection of Clostridium Difficile secondary to antibiotic therapy.
Start therapy with vancomycin and/or metronidazole

19. Prophylactic antibiotics

20. prevention of streptococcal infections in patients with history of RHD
Prevention of TB in close relatives of patient
Prior to surgical procedures
Prevent transmission of hiv from mother to fetus.