General Principles of Infectious Disease. November 2011 Lobna Al Juffali,MSc. Objectives. Recall foundational principles of microbiology, pharmacology, pathophysiology, & immunology in the treatment of infectious diseases
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General Principles of Infectious Disease
Lobna Al Juffali,MSc
We share the world with potential pathogens
Streptococcus (groups A, B, C, G)
Streptococcus viridans group
Moraxella (Branhamella) catarrhalis
Stenotrophomonas (Xanthomonas) maltophilia
Mycobacterium avium intracellulare
Viruses (Hepatitis, Influenza, HIV)
Fungus (Candida, Aspergillus)
Laboratory Tests to direct antimicrobial pharmacotherapy
(gram-positive, gram-negative, gram-variable, bacillus, or cocci).
wet-mount specimen preparations can provide valuable information regarding potential pathogens.
scrapings of mucosal lesions
in cases of suspected meningitis,
Disc diffusion assay
Treat likely / suspected pathogens (usually up to 72 hours)
Treat known / confirmed susceptible pathogen
Use the most effective, least toxic, narrowest spectrum, and most cost effective agent (Drug of Choice)
is the persistent suppression of an organism’s growth after a brief exposure to an antibiotic
A PAE equal to or greater than 1 hour has been demonstrated for most antibiotics against gram-positive bacteria.
As a general rule, antibiotics that inhibit DNA or protein synthesis (e.g., quinolones and aminoglycosides) demonstrate signiﬁcant PAEs against gram-negative organisms.
The primary clinical application of the PAE is to allow for less frequent administration of antimicrobials while still maintaining adequate antibacterial activity
(e.g., extended-interval aminoglycoside administration).
Special concerns regarding antibiotics
Peak and/or trough concentrations are monitored routinely for only a select few antimicrobials(e.g.,aminoglycosides and vancomycin)
It is crucial to ensure that the antimicrobial’s administration time and serum sample time(s)are recorded
Samples ideally should be obtained after steady state is achieved
Combination of the two antibiotic is Signiﬁcantly greater than the sum of activity of either agent alone
combination may result in activity that is worse than either agent alone
indifferent or additive.
Combination activity that is neither synergistic nor antagonistic
White Blood Cell Count (WBC)
e.g Aspiration of infected fluids (sputum, blood, urine, spinal fluid in meningitis, joint fluid in arthritis). Abscesses and cellulitic areas.
When evaluating a patient for initial or empiric therapy, the following factors should be considered:
1. Microorganisms likely to cause infection
2. Anticipated antimicrobial susceptibility pattern
3.Is combination Antimicrobial therapy necessary?
Why do we combine?
B.Criteria for selecting Antimicrobial Therapy