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35 Cards in this Set
- Front
- Back
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What are the 5 components of selecting an appropriate antimicrobial agent?
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1) Establish bacterial etiology
2) Consider spectrum of activity 3) Dispositional characteristics 4) Adverse effects 5) Cost |
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What are 2 reasons to perform in vitro sensitivity?
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-Isolate has an unpredictable response
-Expected response is not achieved |
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True or false. In vitro testing always predicts in vivo efficacy.
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False, may not predict in vivo efficacy
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What are the dispositional characteristics that have to be considered when trying to select an appropriate antimicrobial agent?
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1) Tissue distribution (lipid solubility & ionization state)
2) Function of elimination organ (renal; hepatic) 3) Relationship b/w dosage interval, half life and effect or toxic blood concentrations |
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Why is nephrotoxicity a common side effect?
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Because it eliminates lots of drugs and drugs are filtered and reabsorbed so kidney is exposed to high exposure to high concentrations of drugs
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**What stage of infection are antimicrobials most affective?
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During the acute phase of an infection-earlier you can diagnose and treat the better!
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Why is the prognosis worse when a bacterial infection is diagnosed later compared to sooner?
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-Because bacteria are replicating and growing populations
-Emergence of resistance -With infection get inflammation and cells and fluid and get encapsulation and fusional barriers so harder to get meds to site |
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How can inadequate dosing result in development of resistance?
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Use of inadequate dose or intervals promotes selection of moderately sensitive/resistant strains
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What is combination therapy?
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Treatment of mixed bacterial infections
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When is combination therapy a necessary treatment?
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-Severe infections w/ uncertain etiologies require very broad spectrum therapy
-Wide mutant selection window (MPC-MIC) |
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What are 3 examples of synergistic interactions of antibacterial agents?
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1) Beta-lactams + aminoglycosides (don't generally use bc resistance to both)
2) Beta-lactams + clavulanate 3) Trimethoprim + sulfonamide |
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True or false. It is good to use a combination of bacteriostatic and bacteriocidal drugs.
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False, generally don't want to use combo of bactericidal and bacteriostatic
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What are 2 antibacterial agents that are considered bacteriostatic and are very hard to establish bactericidal concentrations?
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Tetracyclines & sulfonamides
-Easy to get bactericidal concentrations w/ aminoglycosides & beta-lactams |
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What are 4 general interactions that need to be considered when selecting an antimicrobial agent?
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1) Mechanism of action
2) Competition for elimination pathways 3) Effects involving lipid solubility & size 4) Spectrum of activity |
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What is an example of 2 drugs that have a mechanism of action that will compete with each other?
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Chloramphenicol & macrolides (or lincosamides)
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What is an example of competition for elimination of pathways?
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Chloramphenicol is a cytochrome p450 enzyme inhibitor so don't want to combine w/ drugs that rely on cyt p450 for elimination e.g. anesthetics
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What drugs are contraindicated in animals with renal disease?
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Drugs w/ narrow therapeutic indices that are excreted via the kidney
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What drugs need rough dosage modification in animals with renal disease?
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Drugs w/ wide therapeutic indices that are excreted via the kidney
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What drugs require precise dosage modification in animals with renal disease?
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Drugs with narrow therapeutic indices that are excreted via the kidney, but for which there is an essential indication.
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What are 3 drugs excreted principally by the liver?
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1) Chloramphenicola
2) Lincosamides 3) Macrolides |
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What happens to use of drugs excreted principally by the liver (chloramphenicol, macrolides, lincosamides) in animals with liver failure? Renal failure?
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Liver failure: contraindicated
Renal failure: may be used w/o dosage adjustment |
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What are 2 groups of drugs that have wide therapeutic indices & are excreted via the kidney?
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1) Beta lactams
2) Fluoroquinolones |
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What are 4 drugs that have narrow therapeutic indices and are excreted via the kidney?
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1) Neomycin
2) Polymycin 3) Oxytetracycline 4) Nitrofurans -Never put on nylons |
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What are 2 drugs with narrow therapeutic indices that are excreted via the kidney, but for which there is an essential indication?
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Aminoglycosides
Sulfonamides |
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What do you do with beta-lactams and fluoroquinolones in animals with liver failure? Renal failure?
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Liver failure: may be used without dosage adjustment
Renal failure: Halve dose or double dosage interval |
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What do you do when using neomycin, polymyxin, nitrofurans or oxytetracyclines in an animal with liver failure? Renal failure?
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Liver failure: may be used w/o dosage adjustment
Renal failure: Contraindicated |
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What do you do when using aminoglycosaides or sulfonamides on an animal with liver failure? Kidney failure?
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Liver failure: may be used without dosage adjustment
Kidney failure: modification using therapeutic monitoring and/or creatinine clearance values |
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Are beta-lactams, macrolides and lincosamides concentration or time dependent?
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Time above MIC dependent
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What is the optimal dosing regimen for beta-lactams, macrolides and lincosamides?
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Dosing that results in serum concentrations above the MIC for the entire dosage interval
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Are aminoglycosides concentration or time dependent?
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Concentration dependent-need to pay attention to the peak concentration
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With optimal dosing of aminoglycosides we see that some time in the dosage interval is spent underneath the MIC, so why don't the bacteria just flourish?
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Post-antibiotic effect= phenomenon where exposure to a drug causes effects on the bacteria that persist even when the drug concentration falls below the MIC
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What is the dosing schedule for aminoglycosides, why?
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Give pulse doses, where give a high dose at a 12-24 hour interval, allows peak concentration to be adequate but for the concentration to drop below the MIC to account for the post-antibiotic effect
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What is the optimal dosage regimen for aminoglycosides?
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Peak plasma concentration> 8 x MIC
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Are fluoroquinolones time or concentration dependent?
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Concentration dependent-look at peak concentration and area under the curve
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What is the optimal dosing regimen of fluoroquinolones?
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Peak plasma concentration> 10 x MIC
OR 24 hour AUC/MIC > 125 |
