Introduction To Antimicrobial Therapy

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Gram positive bacteria

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a. Purple=positive gram stain
b. Thick PG cell wall with many complex layers (~40)
C. DO NOT CONTAIN AN OUTER MEMBRANE LIKE GRAM NEGATIVE BACTERIA

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Gram negative bacteria

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a. Appear red or pink under microscopy
b. Single PG layer→ simple in complexity
C. HAVE AN OUTER MEMBRANE

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Empiric therapy

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a. Designed to be initiated as soon as an infection is presumed
b. Usually upon presentation with symptoms of an infection
c. Physical evidence of an infection

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Initial antibiotic selection

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i. Based on patient presentation, patient history, current trends in bacterial infections, and current treatment guidelines

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Patient presentation

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i. Physical symptom should guide diagnosis of where the infection is
ii. Antibiotics should be selected that have good penetration to the area of infection

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Patient hx

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i. Where the patient came from can effect which pathogens you should target
ii. Has the patient been on any antibiotics recently?
iii. Does patient have any confounding diseases?

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Current trends

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i. Antibiograms show which pathogens are predominant in institutions
ii. Which drugs may have the best coverage against them?

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Current guidelines

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i. Can direct the physician to decide which agent would be appropriate for each type of infection

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Specific antimicrobial therapy

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a. Follows the results of a culture and susceptibility report
b. Narrow therapy to a single agent against a single organism

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Narrower spectrum antibiotic use

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i. Should be selected if possible

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De-escalation

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1. Discontinuing of multiple empiric agent
2. Studies support de-escalation to decrease antimicrobial resistance, help with cost savings, and to decrease antibiotic use

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Prophylactic antimicrobial therapy

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a. Used for prevention of infection when either sterile sites have a chance of being introduced to bacteria
b. Cases where a patient may have a compromised immune system and need to be protected from infections daily

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Potential risks of antimicrobial therapy

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i. Adverse drug reactions
ii. Increase in drug resistance
iii. Superinfection

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MIC

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i. Minimum inhibitory concentration
ii. Lowest concentration of an antimicrobial agent required to prevent visible growth of a microorganism

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AUC/MIC ratio

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i. Amout of time that the AUC of the antibiotic remains above the MIC
ii. Used to determine efficacy of antibiotic against a microorganism

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MBC

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i. Minimum bactericidal concentration
ii. Lowest concentration of agent required to sterilize the medium or to kill 99.9% of the bacterial count after in-vitro placement

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Bacteriostatic

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i. Drugs which reversibly impair replicating ability of microorganisms
ii. Need the innate immune system to eradicate microorganisms

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Bactericidal

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i. Drugs which irreversibly destroy the ability of a microorganism to replicate
ii. These drugs kill the bacteria without outside assistance from immune system

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PAE

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i. Postantibiotic effect
ii. Persistent effect of an antimicrobial agent on microbial growth following brief exposure of the microorganisms to the antimicrobial agent

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Selective toxicity

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i. Inhibition or destruction of the infecting organism without damage to host cells

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Bacterial killing

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a. Purpose of antibiotics is not to kill 100% of bacteria, but to decrease bacterial load
b. Immune system takes care of rest
c. IC patients have hardest time fighting off infections

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Concentration-dependent killing

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a. Rate and extent of bactericidal action increase with increasing drug concentration
b. Better killing as concentration increases

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Concentration-independent killing

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a. Time dependent
b. Extent of bacterial killing depends on the time the active drug concentration remains above the MIC

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Time-dependent drugs

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b. β-lactams

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MOA of antimicrobials

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a. Inhibition of cell wall synthesis
b. Direct damage to the outer membrane of the bacteria
c. Modification of nucleic acid/DNA synthesis
d. Modify protein synthesis at ribosome
e. Modification of the energy metabolism within the cytoplasm

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Antimicrobial resistance

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a. Pseudomonas, VRE, and MRSA
b. Mechanisms by which the bacteria can acquire resistance can be through both genetic and biochemical pathways
c. These bacteria increase mortality and health care costs as their prevalence increases

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General mechanisms of anitmicrobial resistance

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a. Production of enzymes which inactivate an antimicrobial agent→β-lactamases
b. Alterations in binding sites
c. Decreased concentrations of antibiotic in the bacteria→ porin channels, efflux mechanisms
d. Altered target enzymes

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MRSA risk factors

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i. Antibiotic use in previous 3 months
ii. Hospitalization in past 6 months
iii. History of MRSA colonization
iv. Nursing home resident
v. Any indwelling catheter upon admission
vi. Diabetic

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Classifications of MRSA

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i. CA-MRSA
ii. Healthcare-associated MRSA
iii. Healthcare-acquired MRSA

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Treatment options for MRSA

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i. Vancomycin
ii. Linezolid
iii. Daptomycin (except in pulmonary infections)
iv. Older→ clindamycin, bactrim, tetracyclines

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MDR gram negative risk factors

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i. Broad spectrum antibiotic use in previous 30 days
ii. Hospitalized or nursing home resident in previous 2 weeks
iii. Structural lung disease
iv. Chronic corticosteroid use

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MDR gram negative treatment

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i. Need to add anti-pseudamonal antibiotic
ii. Anti-pseudamonal penicillin
iii. 3rd or 4th generation Cephalosporin
iv. Carbapenem
v. Aztreonam
vi. Aminoglycoside empirically

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β-lactam antibiotics

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a. Penicillin
b. Keflex
c. β-lactam ring attacks PBP, breaks down cell wall of bacteria

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β-lactamase

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a. Breaks down antibiotic β-lactam ring
b. Leads to antibiotic drug resistance

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Penicillinase-resistant antibiotics

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a. Oxicillin
b. Methicillin
c. Prevent β-lactamase from breaking down β-lactam ring
d. Resistance eventually developed

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PBPs in MRSA

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a. MRSA evolved altered PBPs
b. Only one β-lactam antibiotic is able to effectively kill MRSA

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ESBL

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a. Extended spectrum β-lactamases
b. Break down every β-lactam antibiotic
c. Released by gram negative bacteria

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Porin channels

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a. Antibiotic gains entry into bacteria through channels
b. Mutation/evolution of channels leads to blockage of antibiotic entry
c. Gram negative resistance

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Efflux pump

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a. Shoots antibiotics back out of bacteria
b. Gram negative resistance

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Best dosing strategy for concentration-dependent antibiotic

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a. High dose (concentration)
b. Once a day

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Best dosing strategy for time-dependent antibiotics

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a. 4-5*MIC for 50% of the time