EXAM 5 Skin and Soft Tissue Infections Dr. Cluck Flashcards
Know for the EXAM
common organism
how to treat them
MRSA activity (1-2 questions)
Which organisms are part of the normal flora of the skin?
GRAM-POSITIVE
-Coagulase-negative staphylococci
-Corynebacteria (some species are more pathogenic than others, for the most part it is not)
-Propionibacteria
-Streptococci
GRAM-negative (like E.coli) is NOT common on the skin
Fungal
-Candida
-Malassezia sp.
Types of SSTIs
Acute superficial infections
-Impetigo
-Erysepalis
-Lymphangitis
Cellulitis (deeper)
Necrotizing Infections (even deeper, EMERGENCY)
-Fascitis
-Gangrene
Animal and human bites
How does the MLS(B) Staph strain conduct their resistance? To which drugs?
resistant to Macrolides and Clindamycin (lincasomide)
-they bind to the 50S ribosomal subunit and inhibit protein synthesis
Resistance through methylation of the ribosomal target site (erm)
The msrA Staph strain is resistant to which drug? Explain the mechanism.
Macrolides
throws out the drug through the efflux pump
The inuA Staph strain is resistant to which drug? Explain the mechanism.
(rare)
Lincosamides
-inactivation through chemical modification
What induces the MLS(B) resistance?
-Constitutive resistance: the rRNA methylase is always produced, the background stays the same (no zone)
-drug induced: in the presence of Erythromycin (strong inducer) or Clindamycin (weak inducer)
with no resistance: large and round-shaped zone
Which test is used to check for MLS(B) resistance?
D-test
if positive (ICR: induced clindamycin resistance) don’t use Clindamycin - it indicates that resistance may develop (since it was induced during the test by erythromycin)
Which agents are susceptible to Community-Acquired-MRSA?
!!!
Vancomycin (IV)
Linezolid (oral, IV)
Daptomycin (IV)
TMP/SMX (oral)
Clindamycin (oral)
Tetracyclines (Doxycycline, Minocycline) (oral)
Fluoroquinolones (oral)
Which agents are susceptible to hospital-acquired MRSA?
!!!
Vancomycin
Linezolid
Daptomycin
Common IV drugs for MRSA
Vancomycin
Linezolid
Daptomycin
Ceftaroline (5th)
Televancin
Tigecycline/erava/omada
Oritavancin/dalbavancin !!!
MOA Dalbavancin/Oritavancin
long-acting lipoglycopeptides
MOA: hybridized version of daptomycin and vancomycin
-interferes with peptidoglycan cross-linking (binds to D-ala-D-ala terminus of stem peptides
Vancomycin (blocks the enzyme transglycosylase from incorporating into the cell wall)
Daptomycin (integrates into the cell wall, and forms holes -> K+ leakage)
Dosing Dalbavancin and Oritavancin
Dalbavancin:
1000 mg on day 1 and 500 mg on day 8 (studies have shown 1500 mg once is fine)
Oritavancin: 1200 mg once
both have a huge half-life (187h and 393h)
Dalbavancin’s/Oritavancin only FDA indication is…
!!! EXAM Q
for Skin and Soft Tissue infections !!!
only approved for a single dose
How long is a patient therapeutic with one single dose of Dalbavancin?
about 14 days
equivalent to 14 days of Vancomycin
When are two or more doses of Dalbavancin/Oritavancin required?
!!!
Osteomyelitis
1500 mg at day 1
1500 mg at day 8
-bacteremia from SSTI
-dose adjustment needed in renal-impaired patients
Dalbavancin is active against which bacteria? (gram (+) or (-)
No activity against…
gram-positive !!! doesnt cover gram-negative
on the EXAM if there is a gram-negative -> add Pip/tazo, Amox/Clav, Ceftriaxone, Ceftazidime, Cefepime; (Carbapenem, FQ, Tetracycline, Aminoglycoside also cover gram-negatives)
no activity against Vancomycin-resistant enterococci (VRE)
Which drug should be used for an allergic reaction to Dalbavancin?
Benadryl
in general, Dalbavancin is safe in patients who state to have an allergy to Vancomycin
The difference in administration between Dalbavancin vs Oritavancin
Dalbavancin is 1h and compatible with normal saline
Oritavancinc is 3h and in D5W
-> new formulation Kimyrsa is 1h and compatible with normal saline but expensive (6400$)
Dalbavancin vs Oritavancin - Coverage and MOA differences
multiple MOA (inhibits transglycosylation, transpeptidation, and disruption of the membrane)
-more like Daptomycin (bacteriocidal)
-activity against VRE
1200 mg once
(subsequent doses are 800 mg)
Do Dalbavancin and Oritavancin require therapeutic dose monitoring?
No
The SOLOI and SOLOII trial showed what…
compared 1200 mg single dose of Oritavancin with 7-10d of Vancomycin BID in adults with ABSSSI and MRSA infection
What are the contraindications of Oritavancin
-use of unfractionated heparin for 48 hours after giving Oritavancin -> interferes with aPTT
-interferes with coagulation tests (prolongs aPTT and PT/INR)
-concomitant use with warfarin (increases warfarin)
Side effects of Telavancin
(not recommended)
-increases serum creatinine (nephrotoxic)
-prolonged QTc
-foamy urine
the only benefit to Vancomycin:
-1x daily dosing
-doesn’t require therapeutic monitoring
Telavancin Indication
HAP/VAP
in susceptible isolates of Staph aureus and other drugs have failed
Which drug should not be used for Pneumonia?
Daptomycin
pulmonary surfactant !!!
Concerns of Linezolid and why Tidezolid is actually not better
-weak MAOI -> hypertensive crisis
-serotonin syndrome
-myelosuppression, less RBC production from bone marrow (especially after 14 days)
-thrombocytopenia
studies have shown better outcomes, but it was probably underdosed
Pathogens associated with SSTIs
-Injection drug use: Staph aureus !!! Clostridium, E. corrodens, Group A Strep
-Saltwater injury: Vibriovulnificus
-Freshwater injury: Aeromonashydrophila
-Fishmonger: Erysipelothrixrhusiopathiae (intrinsic resistant to Vancomycin), Streptococcus iniae
-Hot tubs: Pseudomonas aeruginosa
The only place where AUC is validated based on the guidelines is..-
invasive MRSA infection (SSTI is not considered invasive)
for usual MRSA: through-based monitoring
What is the purpose of AUC?
FIY
to ensure safety (make sure to prevent nephrotoxicity)
-AUC doesn’t tell how effective the drug is
Which antibiotic can be used for Strep pyogenes?
any ß-lactam works
What most often causes Folliculitis?
-S. aureus
-Hot-tub folliculitis is caused by P. aerigonsa
-clogged hair follicle
Therapeutic approach for Folliculitis?
-Lesions often resolve spontaneously
-Moist heat (up to 3x/day) can facilitate drainage
What is the difference between Furuncles and Carbuncles?
Furuncles
-inflammatory nodules (small abscess)
extending into the subcutaneous tissue
1 pustular opening
VS
Carbuncles
- coalescence of hair follicles which extends into the
subcutaneous fat
more than 1 pustular opening
Which organism causes Furuncles?
What is the treatment for Furuncles and Carbuncles?
S. aureus
incision and drainage - “Drainamicin” HaHa
-smaller furuncles, only moist heat may
be needed
-data of a study says there is a benefit when using 7 days of antibiotics (Bactrim)
->use if surrounding cellulitis
Which organism causes Impetigo?
S. aureus and S. pyogenes
Contagious (stay at home)
A patient presents with a golden crusting sore on the face. Which Skin Tissue Infection is most likely the cause?
Impetigo
Which antibiotic is used for Impetigo?
1st line: topical Mupirocin or retapamulin
-oral therapy:
Antistaphylococcal penicillins
Cephalexin
Clindamycin (in case of penicillin allergy)
-OTC triple antibiotic topical (some activity but inferior)
Which organism causes Lymphangitis, often after a cat bite?
S. pyogenes (Group A strep)
-DOC is penicillin
-> any ß-lactam works EXCEPT Aztreonam (only active against gram-negatives)
A fiery red, tender, painful plaque with demarcated edges is which SSTI?
Erysipelas
Subtype of Cellulits
Which organism causes Erysipelas?
S. pyogenes
others are S. aureus (rare), ß-hemolytic strep (GCS, GGS)
Which antibiotics are used for Erysipelas?
Penicillin VK
-if MSSA is suspected:
Cephalexin
Antistaphylococcal penicillins (nafcillin, oxacillin)
-in penicillin-allergic patients:
Clindamycin or Erythromycin
Which organism causes Cellulitis?
S. aureus and GAS (Group A Strep)
How do we differentiate between cellulitis caused by S. aureus and GAS?
S. aureus induced usually also has abscesses
->drain the abscess -> 7 days of some antistaphylococcal therapy (depending on the organism)
GAS: red and inflamed
What is a key characteristic of a Cellulitis infection? (patient presentation)
it is unilateral
Which disease states mimick Cellulitis?
DVT: red inflamed leg
Venous stasus
Which drugs are considered for Cellulitis treatment?
caused by S. aureus and GAS (Group A Strep): we need Staph and Strep coverage
possible options:
-Antistaphylococcal penicillins
-1st gen cephalosporins (Cefazolin)
-Clindamycin
-MRSA active drugs (if MRSA is suspected)
if the patient comes to the ER, we suspect MRSA
go with Vancomycin !!!
Characteristics of Necrotizing Fascitis
-Painful, hot, swollen, erythematous, shiny
-Blisters
-Subcutaneous gas
-Tense edema outside area of skin
-medical EMERGENCY
cases of Fournier’s Gangrenes need surgery + Antibiotic
What is the difference between Necrotizing fasciitis Type 1 and 2?
Type 1: mixed infection caused by aerobic and anaerobic bacteria (often after surgery or trauma)
Type 2: a monomicrobial infection caused by group
A streptococcus (GAS, MRSA)
How is Necrotizing fasciitis treated?
Type I
surgical intervention (debridement) combined with
antimicrobial therapy and physiologic support
-not Antibiotic alone
-should include anaerobic coverage (Pip/tazo, Meropenem, Metronidazole)
for Type I:
-Vanc + Meropenem
-Vanc + Pip/tazo
-Vanc + Cefepime (doesn’t have anaerobic coverage) + Metronidazole
How is Necrotizing fasciitis treated?
Type II
cover Staph and Strep
-Penicillin + Clindamycin (Protein synthesis inhibitor, so shuts down toxin production)
-may use Linezolid instead (it has great gram (+) coverage and its MOA is to prevent protein synthesis - so it shuts down toxin production)
Which organism commonly causes diabetic foot infections?
Group B Strep !!!
Gram-positive cocci
Treatment for diabetic foot infections
-based on severity, many options
-empirically:
Vancomycin + Cefepime
Vancomycin + Pip/Tazo
until we have an isolate to see the organism
Which organism is usually causes infection after an animal bite?
-Pasturella multocida !!!
-Capnocytophaga canimorsu !!
also:
-Staph aureus
-Staph intermedius !!! Coagulase positive
-Streptococci spp.
-Bartonella henselae - cat stretch disease
-Anaerobes
FYI: Which organism is coagulase-positive?
Staph aureus
Drug of choice for animal bites
Augmentin (Amoxicillin-clavulanic)
(IV version: ampicillin-sulbactam) -> may be used for inpatient
avoid due to poor activity against Pasturella multocida
-cephalexin
-clindamycin
-macrolides (only used for lungs and STI) - wrong answer for SSTI on the EXAM
58y with Fournier’s Grangene A1c=14
A. Cefepime + Clindamycin + Linezolid
B. Ertapenem + Vancomycin
C. Pip/tazo + Vancomycin + Linezolid
D. Meropenem + Linezolid
A. the function of Clindamycin is to prevent toxin production via protein synthesis inhibition, Linezolid does the same - so its double drug use
(Reminder: Clindamycin has anaerobic coverage)
B. Ertapenem has holes in coverage: Pseudomonas, Enterococcus, and Acinobacter are not covered (probably its not one of those organisms that causes it but for empiric we want as much coverage as possible)
C. Vancomycin and Linezolid both cover gram (+) Staph - double coverage, don’t need both
D. correct - Linezolid covers gram (+) and inhibits toxin production and meropenem covers gram (-) and anaerobes
most common seen is
Vancomycin for (+) + Meropenem for (-) + Clindamycin (for toxin)
Organisms causing infections from a human bite
-Staphylococcus aureus (probably secondary)
-Streptococcus spp.
-Peptostreptococcus
-Eikenella corrodens - most often !!!
-Other anaerobes (rarely B. fragilis)
Which organism is usually associated with human bites?
Eikenella corrodens
it is a normal commensal in the mouth
