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What are the major differentials for canine pyoderma? (3 major, 2 minor)
- Staph pseudintermedius
- Staph aureus
- Staph schleiferi subsp Coagulans
- Less common: Pseudomona aeruginosa, enteric bacteria in wounds
What is empirical therapy for canine pyoderma? Why is this the empirical choice?
- Cephalexin PO
- activity against Staph, but no activity against Pseudomonas
- high margin of safety
Why can't you use amoxicillin or penicillin as empirical therapy for canine pyoderma?
Most coagulase + Staph species produce penicillinase (type of beta-lactamase), which inactivates these antibiotics
Coag + Staph MAY have acquired resistance to _______ by the following mechanism...
- cephalexin; an acquired mecA gene encoding PBP2a
- ex. MRSP (exclusive to dogs) and MRSA (mostly humans)- does not have inherent resistance to cephalexin, but may have acquired
How are penicillins potentiated?
- by combining with beta-lactamase inhibitors
- competitively inhibit several bacterial beta-lactamases
Describe the use of potentiated penicillins.
beta-lactamase inhibitors are weakly antibacterial by themselves, but exhibit synergism when combined with a beta-lactam (ie. potentiated penicillins)
What are potentiated penicillin products? What is there route of administration? (2)
- Amoxicillin/ clavulanate- PO
- Ampicillin/ sulbactam- IV
What is the spectrum of potentiated penicillins?
- Same spectrum as whatever penicillin the clavulanate/ sulbactam is combined with PLUS
- more strains of E. coli, Klebsiella, non-MR Staph, Gram - anaerobes
- DOES NOT COVER PSEUDOMONAS
What are the anti-pseudomonal penicillins? How are they administered? (2)
- Ticarcillin- Parenteral (adds coverage for Pseudomonas and even more enterobacteriacea)
- Piperacillin- Parenteral (similar to ticar but $$$), not used much in vetmed
What are the top differentials for a bacterial UTI in a dog? (4)
- E. coli
- enterics (Proteus, etc)
When should you treat a UTI empirically and not?
Can treat empirically at first but should send culture on third occurence
Describe the acquisition of urine for culture, and how this affects interpretation.
- bladder is a sterile site, but urethral is not
- More bacteria tolerated when free catch than with cysto
Enterococcus has intrinsic resistance to __________.
cephalosporins (and maybe others!)
If you see ampicillin on a report, you can assume...
amoxicillin has the same interpretation (ie. if susceptible to ampicillin, it's also susceptible to amoxicillin)
What is the top bacterial differential for post-partum metritis in a cow?
Arcanobacterium (Truperella) pyogenes- Gram + rods
What is a good antimicrobial choice for metritis in a cow?
- CFA (crystalline free acid)- Excede
- HCL- Excenel
- no milk hold for either
What are the third-generation cephalosporins and how is each administered? (6)
- Cefotaxime- parenteral
- Ceftriaxone- parenteral
- Ceftazidime- parenteral
- ceftiofur- parenteral, intramammary
- cefovecin- parenteral (SUBQ!)
- cefpodoxime- PO
What is the only cephalosporin that has anti-pseudomonal activity?
Describe the use of cefovecin.
- long-acting (7-14 days)
- labelled for skin infections in cats (inclu. P multocida abscess) and skin infections in dogs (including pyoderma, Staph pseud, Strep canis)
- commonly used extralabel for UTI
What is cefovecin commonly used for where it is NOT effective?
URI- does not cover URI pathogens, poor resp tract penetration
How many doses of cefovecin can you give?
two at most; if the condition is not better after 4 weeks, you need to reevaluate your diagnosis
What are adverse effects of cefovecin?
- rare anaphylaxis
- injection site edema/ seroma
- mild elevations in ALT, GGT (dogs)
- mild elevations in BUN (cats)
What is the mechanism of action of carbapenems?
disrupt bacterial cell wall by binding PBPs (penicillin binding proteins)
What is the spectrum of carbapenems?
- wide four quadrant coverage- gram + facultatives and anaerobes, gram - facultatives and anaerobes
- good against Pseudomonas aeruginosa
- Enterobacteriacae has resistance
- considered a tertiary drug (big guns!)
What is the route of administration of Imipenem, metabolism, and elimination?
- IV only
- rapidly metabolized by renal dihydropeptidase, so it is usually combined with cilastatin to inhibit dihydropeptidase and prolong activity
- eliminated by kidneys
What is the route of administration and elimination of Meropenem?
- IV (ok to give SQ)
- renal elimination
Meropenem is slightly more potent against _________ than Imipenem.
Describe NDM-1 beta lactamase.
- gene carried on tranmissible plasmids that confers resistance to ALL beta-lactams, including carbapenems
- shard among gram neg bacteria, including E. coli, Klebsiella, Acinetobacter, and Proteus
- common in opportunistic infections in healthcare settings