Antibiotics Flashcards
What is the process for abx (antibiotic) selection?
- Establish presence of infection
- Identify site of infection
- Direct Empiric antibiotic tx towards likely organism
- Identify primary pathogen(s) in the specific pt.
- Choose the most appropriate antibiotic for the PATHOGEN, SITE OF INFECTION, AND PATIENT
What will a gram stain tell you?
Solubility and shape
What will cultures and sensitivities tell you?
What abx is the pathogen sensitive to/ what is it resistant to
What the pathogen is
Quantity of the pathogen
What are the three key things that need to be considered when choosing the most appropriate antibiotic for a pt?
- Pathogen
- Site of infection
- Patient (age, renal function, allergies etc)
t/f? In order to properly identify the infecting pathogen it is good to obtain a culture shortly after starting the pt on an antibiotic?
F. Obtain culture samples prior to abx therapy
t/f? You should always perform blood cultures with any type of infection?
F. You should obtain blood cultures on all acutely ill febrile pt’s. Not every infection warrants a blood culture.
How do gram negative cells appear on microscopy?
RED: Decolorized by alcohol and take on the red color when counterstained with safranin
How do gram positive cells appear on microscopy?
VIOLET: not decolorized by the alcohol so they retain the violet color.
What might be indicated by presence of epithelial cells on a sputum culture?
A bad sample, especially when multiple organisms are identified.
What might recovery of Staph. epidermindis or Corynebacterium from a sterile sample such as CSF, blood, or joint fluid indicate?
Contamination. These are bacteria usually found on the skin
What does the term infection refer to in a culture report?
The isolated organisms are from the specimen and causing the infection.
What does the term colonization refer to in a culture report?
Isolated organisms are from the specimen but are NOT causing the symptoms.
What does the term contamination refer to in a culture report?
The isolated organisms came from the pt’s skin/environment
How soon can you expect results from a C&S?
about 24-48 hours
What does a C&S provide?
The final identification of the organism and information on the effectiveness of antimicrobials.
How are results in a C&S reported?
S-Sensitive
R-Resistant
I-Intermediate
What must you consider when identifying what medication will work for a specific pathogen?
Antimicrobial spectrum of activity, susceptibility testing, and local susceptibility patterns.
Define minimum inhibitory concentration (MIC)
The lowest serum antimicrobial concentration that prevents visible growth of an organism
Define Susceptibility relative to MIC
You can get enough drug into the patient to t the infection (MIC<attainable serum levels)
Define intermediate susceptibility relative to MIC
You may not be able to get enough drug into the pt to tx the infection unless the drug is safe enough to give in high doses or the drug concentrates exceptionally well at the infection site (MIC~/= attainable serum levels)
Define resistance relative to MIC
You cannot get enough drug into the pt to tx the infection (MIC>attainable serum levels)
What drug factors should you consider when prescribing an Abx?
Clinical efficacy (does the drug reach the site of infection) Antimicrobial spectrum Available routes of admin. cost Bactericidal vs. bacterostatic P'kinetics, and P'dynamics Safety (concerns with preg. etc.)
What are “time dependent killers”?
killing is dependent upon the amount of time the organism is in contact with the drug. So the duration that drug concentrations are above the MIC is important.
What are “concentration dependent killers”?
Killing is dependent upon the concentration of the drug that organism is exposed to. The higher the concentration the greater the killing.
When is synergy, or the use of 2 abx used together, used?
enterococcus endocarditis or bacteremia, sepsis, pseudomonal infeections
Define post antibiotic effect (PAE)
Organism growth is suppressed for a period of time after the drug concentration falls below the MIC.
What are the two types of antibiotic resistance?
- Intrinsic resistance
2. Acquired resistance
Define intrinsic resistance
Naturally occurring resistance (drug cannot penetrate the organisms cell wall)
Define acquired resistance
A normally sensitive organism becomes resistant
What mechanisms cause acquired resistance?
- Detoxifying enzymes - alter antibiotic structure and function (ex. ESBL Beta Lactamase - breaks down the beta-lactam ring of pan antibiotics)
- Alteration in antibiotic target site- (Ex MRSA)
- Decreased cellular accumulation of abx. (impaired influx-decreased permeability, and enhanced eflux)
What type of infection is IV admin most often used?
- Severe infections: endocarditis, meningitis, sepsis, osteomelitis
- When pt can’t tolerate oral meds or has non-functioning GI tract
MOA Beta-Lactams
Bind to penicillin binding proteins and inhibit cell wall synthesis causing cell death.
What are the 4 subclasses of PCN?
Natural PCN
Aminopenicillins
Penicillinase resistant PCN
Extended spectrum PCN
What do Natural PCN cover (Gram +/-, anaerobes?)
Gram +, a few Gram -
What do Aminopenicillins cover (Gram +/-, anaerobes?)
Gram +, some Gram -
What do Penicillinase resistant penicillins cover (Gram +/-, anaerobes?)
Gram + only
What do extended spectrum penicillin /beta-lactamase combo cover (Gram +/-, anaerobes?)
Gram +, Gram -, and anaerobes
What medications are Natural PCN?
PCN VK
PCN G
What is the spectrum of activity for PCN VK and PCN G? and what is the most common use?
GRAM +: Strep Pyogenes
Some Gram -: Pharyngitis, erysipelas, and syphilis (PCN G)
T/F >90% of staph produce penicillinase so PCN is not effective
TRUE
What medications are Aminopenicillins?
What are the most common uses?
Ampicillin
Amoxicillin (amoxicillin/clavulanate)
URI, Enterococcal infection, amox/clavulunate used for skin infections, UTI, CAP, Lymphadenitis
What meds are penicillinase resistant penicillins?
Dicloxacillin
Nafcillin-IV
Oxacillin-IV
Methacillin (pulled from market)
What bacteria does PCNase resistant PCN cover?
What are the most common uses.
Gram Positive; Staphylococcus spp, and Streptococcus spp.
Drug of choice for B-lactam producing staph
Used to tx - cellulitis, endocarditis
What are extended-spectrum penicillins?
Tirarcillin/clavulanate
Piperacillin/tazobactam
*the “big guns” only available IV
What bacteria do Extended-sepctrum pcns cover?
Common uses?
Gram positive: Streptococcus, Staphylococcus (MSSA)
Gram negative: Enterobacteriaceae (E. Coli, proteus)
Anaerobes: Bacteriodes
Nosocomial pneumonia, Intra-abdominal infections, Skin and soft tissue infections
MOA for B-lactamase inhibitors?
Enhances the antimicrobial activity against certain beta-lactamase producing organisms, extending the abx antimicrobial spectrum
What bacteria are covered by B-lactamase inhibitors?
Gram positive-S. aureus
Anaerobes-bacteriodes sp.
Gram negative- H. flu, E coli
ADE PCN
Rash
Anyphylaxis, angioedema
Ampicillin/amoxicillin - GI upset/diarrhea
Options for management of PCN allergy?
Option 1 - administer a cephalosporin
Option 2 - Prescribe/recommend a non beta-lactam abx.
Option 3 - Perform pcn desensitization
Option 4 - Perform a PCN skin test 80-95% of
What are the renal adjustments for PCN’s
Must adjust for PCN, Amoxicillin/ampicillin
No adjustment for Dicloxacillin, nafcillin, oxacillin
What DI does Probenecid have with PCN?
Probenecid decreases the renal tubular secretion of PCN’s co-admin causes increased serum levels of abx.
Which of the following abx would be the best choice for treatment of cellulitis caused by Staph aureus (MSSA)? A. Amoxicillin B. Piperacillin/tazobactam C. Penicillin D. Nafcillin
D. Nafcilin-Is a PCNase resistant PCN and is drug of choice for B-lac producing staph
Amox-is broken down by B-lac
Piperacillin/tazo is empiric and very broad-an option but not specific enough
PCN-is broken down by B-lac
What are the 5 groups of Cephalosporins?
1st gen 2nd gen 3rd gen 4th gen Newer gen
(4th and newer gen are IV only)
Which drugs are first generation cephalosporins?
Cephalexin-oral
Cefazolin-IV
What drugs are 2nd generation cephalosporins?
Cefuroxime-oral
Cefoxitin-IV
What drugs are 3rd gen Cephalosporins?
Cefpodoxime-oral
Ceftriaxone-IV
What drugs are 4th gen cephalosporins?
Cefepime-IV
Newer gen
IV only
What do first gen cephalosporins cover?
Gram positive
some Gram negative
What do 2nd gen cephalosporins cover?
Gram pos
some increased gram neg
What do 3rd gen cephalosporins cover?
Less gram positive
More gram neg
What do 4th gen cephalosporins cover?
Gram pos
Gram neg
What is the spectrum of activity for First gen cephalosporins?
Gram positive: Staphlococcus, Streptococcus spp.
Gram negative: Proteus, Escherichia coli, Klebsiella pneumoniae
(SPEcK)
What are the common uses for first gen cephalosporins?
Mild skin or soft tissue infections
What is the spectrum of activity for 2nd gen cephalosporins?
Gram positive: Staphlococcus, Strepococcus spp.
Gram Negative: H. flu, Moraxella catarrhalis, Proteus mirabilis, E. coli, Klebsiella pneumo.
(HMSPEcK)
What is the spectrum of activity for 3rd gen cephalosporins?
Gram positive: Strep pneumo
Gram Negative: Enterobacteriaceae, H. flu, Moraxella catarhalis.
Common uses for 3rd gen cephalosporins?
CAP
OM
URI