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142 Cards in this Set
- Front
- Back
Criteria of clean surgical wounds:
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elective, primarily closed, undrained, nontraumatic, uninfected, no break in technique, no inflammation encountered, respiratory, urogenital or gi tract not entered
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Criteria of clean-contaminated surgical wounds:
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GI or respiratory tract entered without significant spillage, oropharynx entered, vagina entered, GU entered in absence of infected urine, minor break in technique
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Criteria of contaminated surgical wounds:
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major break in technique, gross spillage from gi tract, fresh traumatic wound, entrance of GU or biliary tract in presence of infected bile or urine
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Criteria of dirty surgical wounds:
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acute bacterial inflammation entered, transection of clean tissues to gain access to pus, traumatic wound with retained devitalized tissue, foreign bodies, fecal contamination, or delayed treatment
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Sources of bacterial contamination in a surgical procedure:
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air, patient, surgeon, instrumentation
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Recommendations for reducing airborne bacteria:
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positive air pressure in OR, filtering >90% of air, exchanging air 15 time/ hr, air introduced from ceiling and exhausted at floor
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How does hair removal affect risk of SSI?
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Hair removal did not reduce # of CFU compared with leaving hair; shaving increases risk of SSI compared with clipping
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Why is shaving associated with an increase risk of SSI?
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Results in microscopic cuts to the skin that serve as foci for bacterial multiplication
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What is the most common source of bacteria in SSI?
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Direct inoculation by endogenous flora
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What is the most common pathogen associated with musculoskeletal SSI?
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Staphylococcus aureus
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What is the most common pathogen associated with long bone fracture or arthrodesis SSI?
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Enterobacter
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Equation for risk of SSI:
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risk of SSI = dose of bacterial contamination x virulence / resistance of host
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Examples of microbial virulence factors:
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bacterial adhesion molecules, exotoxins, secreted proteins, production of biofilm
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Define biofilm:
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adherence to and production of a glycocalyx film
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Examples of patient related risk factors for SSI:
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extremities or age, female gender, immunocompromise due to corticosteroid use, FPT, weight, distant sites of infection, local or systemic hypoxemia, presence of foreign material
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What is the relationship between duration of surgery and risk of SSI?
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General ortho procedures over 90 minutes increased risk by 3.6; as duration increased for long bone fracture repair the risk of SSI increased; incisional complications are twice as likely if abdominal surgery is > 2 hours
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What is the rate of MRSA colonization in hospitalized horses?
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2.3%
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What is the rate of clinical MRSA nosocomial infection in hospitalized horses?
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0.18%
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What acute phase proteins are commonly measured?
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Fibrinogen, serum amyloid A, haptoglobin
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What are the differences in fibrinogen and SAA measurements for SSI detection?
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Fibrinogen has a lengthy response to inflammation so is insensitive for SSI detection, SSA has rapid and large changes so more sensitive for SSI
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Methods to improve bacterial culture growth:
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use of enrichment broth, obtain before administering antibiotics or withhold antibiotics for 24 hours prior to sample selection
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Most common isolates in long bone fracture SSI:
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gram negative- enterobacter cloacae, gram positive- coagulase negative staphylococcus
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Most common isolate in post-operative synovial infections:
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staphylococcus aureus
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What are the basic principles for treating SSI?
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Drain infected tissues aided by gravity; debride devitalized and infected tissue; appropriate therapeutic antimicrobial therapy based on culture & sensitivity
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How do concentration dependent antibiotics function?
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Rely on the ration of the peak plasma concentration of the antibiotic to the MIC of the bacteria
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What is the optimal peak plasma antibiotic concentration to MIC ration for concentration dependent antibiotics?
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10:1 or 12:1
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How do time dependent antibiotics function?
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Depend on a saturable concentration effect for bacterial killing (at some point there is no additional benefit of higher concentration of drug)
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How do concentration and time dependent antibiotics differ in dosing?
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Because concentration dependent reliant on ratio dosing interval is long and higher doses, time dependent antimicrobials have more frequent dosing with smaller doses to be effective
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What is the difference between antimicrobial prophylaxis and therapeutic antimicrobials?
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Antimicrobial prophylaxis is a very short term administration protocol given prior to surgical intervention, therapeutic antimicrobial therapy refers to treatment of an established infection
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What are the principles of prophylactic antimicrobials?
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Antimicrobials only used when benefits have be demonstrated by clinical trial or the risk of SSI would be catastrophic; safe, inexpensive, bactericidal antimicrobial chosen with activity against most likely pathogens; appropriate time of administration; tissue levels of antimicrobial maintained throughout surgery and for a few hours after incision closed
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When should prophylactic antibiotics be administered in relation to surgery?
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Within 1 hour of incision
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When does prophylactic antimicrobial administration become unnecessary?
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After 24 hours
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What is post antibiotic effect?
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Period of time after the antimicrobial concentration has fallen below MIC when growth of targeted bacteria continues to be suppressed
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What does the post antibiotic effect depend on?
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Antibiotic concentration, duration of exposure to the antibiotic, bacterial species, antimicrobial used
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What is the benefit of extended interval dosing?
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Concentration dependent antimicrobial activity maximized by optimizing peak plasma concentrations, time dependent toxicity minimized, post antibiotic effect maximized, adaptive resistance is limited
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MOA of sulfonamides:
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competitive substitution of PABA in conversion of PABA to dihydrofolic acid
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MOA of trimethoprim:
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inhibit dihydrofolic acid reductase which would convert dihydrofolic acid to tetrahydrofolic acid
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What are the advantages of local antimicrobial therapy?
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Exposure of pathogen to extremely high concentrations of antimicrobial drugs; avoid adverse effects of systemic doses; deliver high dose of drugs that would be cost-prohibitive systemically
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What are the disadvantages of PMMA?
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Not absorbable and heat labile antibiotics can not be incorporated
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What is the ratio of antibiotic to PMMA?
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1-2g antibiotic to 10g PMMA
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What can weaken the biomechanical properties of PMMA?
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greater than 10% antibiotic to PMMA
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What antibiotics have been incorporated into PMMA?
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Gentamicin, amikacin, tobramycin, cephalosporins, enrofloxacin
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How are PMMA beads re-sterilized?
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Ethylene oxide sterilization
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What are the benefits of POP over PMMA?
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POP is less expensive and will slowly degrade over time
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What is the rate of elution of antibiotics from POP?
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80% within the first 2 days
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What are the disadvantages of POP vs. PMMA?
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The set up time of POP is slower
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What is the usual dosing recommendation for RLP?
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1/3 of systemic dose diluted to 30mL (distal limb) or 60 mL(upper limb)
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What is the MOA of renal toxicity of aminoglycosides?
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Drug accumulation in the proximal renal tubules by the organic ion transport system
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What is the cause of resistance in MRSA?
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Production of an altered penicillin-binding protein called PBP2a
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What gene is responsible for the production of PBP2a by MRSA and where is it located?
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mecA is located in the staphylococcal cassette chromosome (SCCmec)
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What is the significance of staphylococcal cassette chromosome mec?
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The mec gene is responsible for PBP2a which confers resistance to beta lactams and cephalosporins and downstream from mec in this cassette is a variable segment in which other genes conferring resistance can be added
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How are MRSA strains seen in horses different from human and small animals?
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The strains common to horses are uncommon in humans and small animals (although strains common in humans are common in small animals) humans can acquire horse strains of MRSA, veterinarians exposed to horse strains of MRSA are likely to carry these strains in nasal passages (8-15.6%)
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MIC:
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minimum concentration of antibiotic that will visible inhibit bacterial growth after overnight inoculation
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Penicillin static or cidal
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Bactericidal
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Penicillin MOA
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Inhibit cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis
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Penicillin adverse effects
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Autoimmune hemolytic anemia, anaphylaxis, transient hypotension, increased large intestinal motility, cardiac arrhythmia
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Cephalosporins static or cidal
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Bactericidal
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Cephalosporins MOA
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Inhibit cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis
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Cephalosporins adverse effects
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Enterocolitis
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Bacterial resistance mechanisms to beta lactams:
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altered or different PBP, efflux through specific pumps, loss or change in porins, inactivation by beta-lactamases
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Aminoglycoside static or cidal
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Bactericidal
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Aminoglycoside MOA
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Inhibit protein synthesis by binding to 30S ribosomal subunit, required oxygen!
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Aminoglycoside adverse effects
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Nephrotoxicity, neuromuscular blockade, ototoxicity
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Bacterial resistance mechanisms to aminoglycosides:
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decreased cell entry, altered ribosome structure, destruction by microbial enzymes within cell
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Fluoroquinolone static or cidal
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Bactericidal
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Fluoroquinolone time or concentration:
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concentration
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Fluoroquinolone MOA
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Inhibits bacterial DNA gyrase
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Fluoroquinolone adverse effects
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Cartilage disorders in young (< 3 years old) horses, oral ulceration
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Metronidazole static or cidal
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Bactericidal
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Metronidazole MOA
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Disrupts bacterical DNA by free radicals and unstable intermediate compounds after structural change once in target organism; causes DNA breakage and inhibition of DNA repair
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Metronidazole adverse effects
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Enterocolitis, inappetence
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Trimethoprim sulfonamides static or cidal
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Bactericidal when combined. Sulfa static.
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Trimethoprim sulfonamides MOA
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Synergistic action to inhibit folic acid synthesis (sulfonamides block first step and trimethoprim blocks second stop in folic acid synthesis pathway)
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Trimethoprim sulfonamides adverse effects
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Idiosyncratic reaction
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Tetracyclines static or cidal
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Bacteriostatic
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Tetracyclines MOA
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Inhibit protein synthesis by reversibly binding to 30S ribosomal subunit
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Tetracycline adverse effects
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Nephrotoxicity, discoloration of urine and erupting teeth
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Bacterial mechanisms of resistance to tetracyclines:
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plasmid mediated
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Chloramphenicol static or cidal
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Bacteriostatic
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Chloramphenicol, florfenicol MOA
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Inhibit protein synthesis by reversibly binding to 50S ribosomal subunit
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Chloramphenicol adverse effects
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Reversible aplastic anemia (idiosyncratic anemia in humans)
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Bacterial mechanisms of resistance to phenicols:
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destruction by microbial enzymes (chloro > florfen)
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Macrolides static or cidal
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Bacteriostatic
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Macrolides MOA
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Inhibit protein synthesis by reversibly binding to 50S ribosomal subunit
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Macrolide adverse effects
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Intestinal prokinetic
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Bacterial mechanisms of resistance to macrolides:
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pump efflux from cell, altered ribosome
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Concentration dependent antibiotics
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Aminoglycosides, sulphas, rifampin, macrolides, tetracyclines, chloramphenicol, metronidazole, vancomycin, fluoroquinolones
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Time dependent antibiotics
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Beta lactams, cephalosporins
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Common aminoglycosides
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Amikacin, gentimicin
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Common beta lactams
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Penicillins (PPG, Potassium pen), ampicillin, amoxicillin
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Common macrolides
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Erythromycin, clarithromycin, azithromycin, in FA tulathromycin ("Draxxin") and tilmicosin ("Micotil")
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Common fluoroquinolones
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Enrofloxacin
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Spectrum of penicillins
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Excellent gram +, poor gram -, good anaerobes
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Spectrum of ceftiofur
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excellent gram + and -, good anaerobes
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Spectrum of aminoglycosides
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Poor gram +, excellent gram -, no anaerobes
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Spectrum of sulphas
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Excellent gram +, -, good anaerobes
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Spectrum of macrolides
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Excellent gram +, poor gram -, poor anaerobes
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Spectrum of fluoroquinolones
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Poor gram +, excellent gram -, no anaerobes
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Spectrum of tetracyclines
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Excellent gram +, -, anaerobes
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Spectrum of chloramphenicol
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Excellent gram +, -, anaerobes
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Spectrum of metronidazole
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Only anaerobes
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Spectrum of vancomycin
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Only gram +
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Penicillins time or concentration
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Time
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Cephalosporins time or concentration
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Time
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Aminoglycosides time or concentration
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Concentration
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Sulphas time or concentration
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Concentration
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Rifampin time or concentration
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Concentration
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MOA rifampin:
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inhibits RNA synthesis
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Spectrum of rifampin:
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primarily gram +
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Macrolides time or concentration
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Concentration
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Fluoroquinolones time or concentration
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Time
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Tetracyclines time or concentration
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Concentration
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Metronidazole time or concentration
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Concentration
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Vancomycin time or concentration
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Concentration
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MOA lincosamides:
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inhibit 50S ribosomal subunit
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what is an s-type infection?
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infection in foals with only the synovial membrane and synovial fluid involvement
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conditions related to s-type infections:
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very young foals (< 1 week) usually larger joints and usually multiple joints
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what is an e-type infection?
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infection of the epiphyseal complex in foals
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conditions related to e-type infections:
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weeks old foals, usually multiple joints, history of FPT or other disease such as pneumonia or diarrhea, mild or intermittent lameness with or without fever
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what is a p-type infection?
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infection of a long bone physis in foals with or without joint involvement
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conditions related to p-type infections:
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usually older foals, extension into joint usually at attachment of joint capsule, no history of pre-existing disease, usually only a single site of infection
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clinical pathology associated with septic arthritis in foals:
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hyperfibrinogenemia with type e and p infections
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common p-type bacteria:
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strep, rhodococcus, actinobacillus, enterbacteriaeae
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most common pathogen in post-injection septic arthritis
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staph aureus
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most common pathogen in traumatic septic arthritis
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enterobacteriaceae
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radiographic evidence of type s infection
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soft tissue density with marked effusion
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radiographic evidence of type e infections
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subchondral lytic defect
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radiographic evidence of type p infections
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large lytic lesion extending to the outer cortex of the bone
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cause of sequestrum formation
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stripping of the periosteum and loss of blood supply leads to necrosis of a segment of bone
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what is a seqestrum
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necrotic bone separated from healthy bone
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what is an involucrum?
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reactive bone that forms around a sequestrum
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what is a cloaca?
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draining tract to the skin connecting to the opening of the sequestrum
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treatment of bone sequestra:
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if there is minimal tissue reaction and a small piece of bone, time and appropriate antimicrobial therapy should resolve the infection otherwise removal of the sequestrum and debridement are indicated with local antibiotic therapy or bone graft at the site of debridement
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disadvantage of gentamicin collagen sponges
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short elution, quick absorption
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advantage of antibiotic plaster of paris
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very inexpensive
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disadvantage of antibiotic plaster of paris
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slow to harden
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examples of biodegradable biomaterials for local antibiotic delivery
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collagen sponges, plaster of paris, hydroxyapatite, dextran gel (R gel)
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disadvantage of hydroxyapatite for local antibiotic delivery
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expensive
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advantages of dextran gel (R gel)
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variety of antibiotics available, easy to use
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example of non biodegradable biomaterial for local antimicrobial delivery
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PMMA
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advantage of antibiotic PMMA
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easy to use, good elution properties, excellent biocompatibility
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disadvantage of antibiotic PMMA
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very exothermic curing so can not be used with heat sensitive antibiotics
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