Pharmacology: General principles and Beta-lactams Flashcards
Are enterococcus gram negative or gram positive?
Gram positive
What are the major enteric gram negatives?
PEK: Proteus spp., E. coli, Klebsiella pneumoniae
What are the “nasty” gram negatives?
Pseudomonas aeruginosa, Acetinobacter baumanii
What is empiric versus definitive therapy?
Empiric - probability-based therapy used before causative organism is known for sure
Definitive - therapy used once organism is cultured and antibiotic sensitivity is known
What is bactericidal versus bacteriostatic? When is this relevant?
Bactericidal - number of bacteria decrease
Bacteriostatic - number of bacteria stay the same for innate immune clearance
Relevant in immunocompromised patients who will not be able to clear an infection from bacteriostatic antibiotics, or in serious infections of immune-compromised places like meningitis or endocarditis
What is pharmacokinetics?
Kinetics - What the body does to the drug, including absorption, distribution, metabolism, and secretion
What is pharmacodynamics?
Dynamics - What the drug does to the body, or the bug at the site of action
Includes concentration-dependent or time-dependent killing
What is MIC?
Minimum inhibitory concentration
The lowest concentration of the antimicrobial which inhibits growth (bacteriostatic) in a test tube
What is defined as susceptible for antimicrobials?
The PK/PD targets are achievable and you would expect common doses of the antimicrobial to lead to clinical success of organism clearance
What is defined as intermediate susceptibility for antimicrobials?
MICs are elevated, but one MIGHT see clinical success with optimal dose-optimization strategies like continuous IV drug infusion
What is defined as resistant for antimicrobials?
PK/PD targets are not obtainable, and clinical success would not be expected with the agent
What are the “time dependent” antimicrobials and what does this mean?
Amount of time > MIC is the only thing that matters
- Beta-lactams
- Macrolides
- Oxazolidinones
What is an AUC antimicrobial and what drugs full in this class?
Area under the curve matters, a combination of dosage and time
Most drugs fall in this class
What antimicrobials are concentration-max dependent?
Aminoglycosides
What is the most common site of action for antimicrobials?
Ribosomes
What are the major mechanisms of resistance to antimicrobials?
- Modify the antimicrobial enzymatically
- Alter the target site
- Decrease its concentration in the cell (efflux pumps or downregulation of porins which transport the drug into the cell)
What is the mechanism of action of beta-lactams?
Inhibit the transpeptidation enzymes (penicillin-binding proteins) which catalyze the last step of cell wall synthesis - cross-linking of peptidoglycan
What is penicillin used for?
1st line treatment for Streptococci and E. Faecalis, as well as syphillis
What type of penicillin is used to treat syphillis?
Benzathine penicillin - long-acting and low level of drugs (only extremely susceptible bugs can be treated this way)
What is the difference between penicillin, cephalosporins, carbapenams, and monobactims?
The beta-lactam structure (number of ring and its members)
How does beta-lactamase work? What is one called?
Hydrolyzes the beta-lactam ring, opening it up so it cannot bind PBP anymore
I.e. penicillinases, cephalosporinases, carbapenemases
Are beta-lactamases more common in gram negative or gram positive and why?
Gram negative -> enzyme can be held in periplasmic space rather than secreted into extracellular space
Why is penicillin important for dentists?
It has good streptococcal dental coverage to prevent endocarditis associated with this microbes
What are the two clinically important 2nd generation penicillins? How is the second generation different?
- Nafcillin - IV
- Dicloxacillin - PO
Second generation is pencillinase resistant
What are antistaphylococcal penicillins? When can they be used?
Nafcillin - given IV for treatment of MSSA. Naf for Staph
Not usable against MRSA
- methicillin is a second generation that indicates susceptibility
What is the orally given second generation penicillin?
Dicloxacillin
How does staph resist second generation penicillins?
Make PBPs with decreased affinity for Beta-lactams, which can carry out cross-linking
This confers resistance to all beta-lactams
What are the two types of aminopenicillins and how are they given?
Ampicillin - IV
AmOxicillin - PO, better oral bioavailability
What spectrum do aminopenicillins?
HELPS bugs H - Haemophilus influenzae E - Enterococcus faecalis L - Listeria monocytogenes P - Proteus mirabalis S - Salmonella and Shigella