Antibiotics in general Flashcards
What affects serum antibiotic levels?
Absorption, volume of distribution, metabolism, and excretion all affect serum antibiotic levels.
What is MIC?
Mean inhibitory concentration
What is MBC?
Minimal bactericidal concentration
How do you maximize success with B-lactam antibiotics?
Serum levels should be above the MIC for at least 50% of the time.
How do you maximize success with ahminoglycosides and fluoroquinolone?
High peak concentration and high AUC/MIC ratio
How can you prevent antibiotic resistance?
High doses to achieve very high AUC/MIC ratios, 50-200, depending on the organism. Also, short courses of antibiotics, ideally 5 days or less, can reduce resistance
What is the 3-day rule?
Narrow antibiotics within three days! Within 3-4 days following the administration of antibiotics, sequential cultures of mouth flora reveal that the numbers and types of bacteria begin to change significantly. Normal flora die, and resistant GN rods, GP cocci, and fungi begin to predominate.
How is serum procalcitonin useful in evaluating infection?
In response to bacterial infection, this precursor of calcitonin is synthesized and released into the serum by many organs in the body.
How is serum procalcitonin useful in evaluating infection?
In response to bacterial infection, this precursor of calcitonin is synthesized and released into the serum by many organs in the body. Production of interferon (IFN) in response to viral infection inhibits this synthesis. Levels can also aid in prognosis.
How can you differentiate between colonization and infection?
- Growth of resistant organisms is the rule in the patient on antibiotics.
- Antibiotics should be switched only on evidence of a new infection.
- Evidence for a new superinfection includes
- new fever or worsening fever pattern
- increased peripheral leukocyte count with left shift
- increased inflammatory exudate at the original site of infection
- increased PMNs on gram stain, and
- correlation between bacterial morphology on Gram stain and culture
What are the B-lactam antibiotics?
Penicillins, cephalosporins, and carbapenems
What is required for B-lactams to work?
Active bacterial growth and active cell wall synthesis. Therefore, bacteria in a dormant or static phase will not be killed, but those in an active log phase of growth are quickly lysed.
What are the most common toxicity concerns in B-lactams?
Allergic reactions, both delated and immediate hypersensitivity reactions. Penicillin reactions are seen in 1-10%. 1-7% of patients allergic to PCN are also allergic to cephalosporins and carbapenems.
- Ceftriaxone is excreted in the bile and can crystallize to form biliary sludge
- Cephalosporins with methylthiotetrazole rings can interfere with vitamin K and increase prothrombin time
- Nephrotoxicity can occur when cephalosporins are combined with ahminoglycosides.
What are the natural penicillins?
PCN G
Procaine PCN G
Benzathine PCN G
PCN V-K
Are the natural PCNs broad or narrow?
Narrow
