Lecture 4: Antimicrobial drug selection

Define “empirical” antimicrobial drug therapy

The initiation of antimicrobial drug therapy before ID of the infecting microorganism and its antibiotic susceptibility.

Describe the process of case selection- how do you decide which patients to treat with an antimicrobial drug? What conditions must be present to justify treatment with an antimicrobial drug?

Ask the following questions: Is it a bacterial infection? Does it require treatment w/ an antibacterial drug? What is the most likely pathogen? Can we identify the pathogen?

When should microbial culture (& susceptibility?) be performed?

If there is retreatment/reoccurrence or treatment failure

What is the simplest way to accurately determine the best way to collect, store, and ship samples for bacterial culture at a diagnostic laboratory?

Call the VDL

What do you need to know about a drug in order to achieve the goals for antimicrobial drug therapy:

1. The pathogen is susceptible to the drug

2. Sufficient drug concentration can be achieved at the site of the infection

3. The patient can tolerate the drug at the dosage used

Describe the steps to be followed in empirical selection of an antimicrobial drug to treat an infectious disease.

Try to choose the most narrow-spectrum drug w/ an appropriate spectrum for the most likely pathogen. Avoid critically important drug classes if you can.

What is the clinical implication of a drug being characterized as “bacteriostatic” or “bactericidal”?

Bactericidal kills bacteria, bacteriostatic inhibits bacterial growth. There are both equally effective and should not be used to determine the effectiveness of the antibacterial therapy.

When Is IV administration of an antibacterial drug indicated?

When an oral drug cannot be effectively administered, absorption or oral drug may be impacted by concurrent disease, or the optimal drug does not have good oral antimicrobials.

Are critically important antimicrobial drugs/classes always more effective than less important ones? Give an example of when a non-critically important drug/class would be expected to be more effective or equally effective compared to a critically important drug/class.

No they are not more effective than the less important ones. Vancomycin is less effective than low tier beta-lactams for treatment of MRSA in humans.

What is the primary focus when selecting an antibacterial drug for empirical use?

a) Cost of the drug

b) Spectrum of activity

c) Availability of the drug

d) Ease of administration

b) Spectrum of activity

Empirical antimicrobial drug use is defined as:

a) Using critically important drug classes

b) Always performing a culture and sensitivity test first

c) Initiating antimicrobial drug therapy before identifying the infecting microorganism and its antibiotic susceptibility

d) Using the most expensive drug available

c) Initiating antimicrobial drug therapy before identifying the infecting microorganism and its antibiotic susceptibility

Which of the following is NOT a commonly used class of antibacterial drugs?

a) Penicillins

b) Cephalosporins

c) Macrolides

d) Antifungals

d) Antifungals

What is the most common pathogen in urinary tract infections?

a) Klebsiella

b) E. coli

c) Salmonella

d) Proteus

b) E. coli

What should you consider FIRST for uncomplicated UTIs in companion animals, according to the source?

a) NSAIDs

b) Fluoroquinolones

c) Aminoglycosides

d) Chloramphenicol

a) NSAIDs

If NSAIDs are not effective for a UTI in a companion animal, what is the 1st choice antimicrobial to use, according to the source?

a) Amoxicillin

b) Fluoroquinolones

c) Aminoglycosides

d) Chloramphenicol

a) Amoxicillin

Which of these antimicrobials is ineffective against anaerobes?

a) Penicillin

b) Metronidazole

c) Fluoroquinolones

d) Chloramphenicol

c) Fluoroquinolones

Which of these antimicrobials has activity in all 4 quadrants (Gram+, Gram-, aerobic, anaerobic) but is not a 1st line choice?

a) Penicillin

b) Tetracyclines

c) Fluoroquinolones

d) Chloramphenicol

d) Chloramphenicol

What should be done if the first empirical treatment for a bacterial infection fails?

a) Keep trying different drugs until one works.

b) Perform a culture and sensitivity test.

c) Use a critically important drug class.

d) Assume the patient will not recover.

b) Perform a culture and sensitivity test.

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What is a key pharmacokinetic consideration when choosing a beta-lactam for bacterial cystitis?

a) Poor penetration into the prostate gland

b) Elimination unchanged in the urine

c) Concentration in the liver

d) Limited oral bioavailability

b) Elimination unchanged in the urine

According to J. Scott Weese, what is a common misconception about antimicrobials?

a) Bactericidal antimicrobials are more effective than bacteriostatic antimicrobials

b) IV antimicrobials are never required in patients with severe disease

c) Higher-tier antimicrobials are always more effective

d) Shorter courses of antibiotics always lead to antimicrobial resistance

a) Bactericidal antimicrobials are more effective than bacteriostatic antimicrobials

According to J. Scott Weese, is it necessary to complete the entire course of antibiotics prescribed?

a) Yes, to reduce the emergence of resistance

b) Yes, to ensure all bacteria are eliminate

c) No, continuing to take the drug once the infection is resolved only selects for resistance

d) Yes, to prevent recurrence of the infection

c) No, continuing to take the drug once the infection is resolved only selects for resistance

What is one of the factors to consider when prescribing or dispensing antibacterial drugs? a) The cost of the drug b) The color of the drug c) Factors to be considered when prescribing or dispensing antibacterial drugs d) The availability of the drug in the clinic

c) Factors to be considered when prescribing or dispensing antibacterial drugs

What is one of the key components of antimicrobial effectiveness?

a) The cost of the drug

b) The amount of drug present at the infection site

c) The color of the drug

d) The availability of the drug in the clinic

b) The amount of drug present at the infection site

What is one of the examples where antimicrobial drug treatment is NOT clearly beneficial?

a) Severe mastitis in cows

b) Most acute cases of mild-to-moderate Gram-mastitis in cows

c) Chronic mastitis in cows that are likely to resolve

d) Septicemia in dogs

b) Most acute cases of mild-to-moderate Gram-mastitis in cows

What is a good reason to call the Veterinary Diagnostic Lab (VDL)?

a) To get a free sample of antibiotics

b) To complain about the cost of testing

c) If you're unsure about what sample to take, or how to submit it, or what to ask for

d) To ask for a date with the lab technician

c) If you're unsure about what sample to take, or how to submit it, or what to ask for

What is the goal in empirical selection of a drug?

a) Try to choose the broadest-spectrum drug available.

b) Try to choose the most narrow- spectrum drug with an appropriate spectrum for the most likely pathogen

c) Select the most expensive drug available

d) Always use a critically important drug

b) Try to choose the most narrow- spectrum drug with an appropriate spectrum for the most likely pathogen

For a common infection, what should you do?

a) Prescribe a high-tier antibiotic immediately

b) Ignore guidelines and treat based on personal experience

c) Consult available and useful guidelines

d) Always perform surgery first

c) Consult available and useful guidelines

What is the first question to ask yourself when considering antimicrobial therapy?

a) Is there a bacterial infection?

b) What is the most expensive drug I can prescribe?

c) What is the newest drug on the market?

d) Can I get away without prescribing anything?

a) Is there a bacterial infection?

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What is one of the "big three" considerations when picking an antimicrobial drug?

a) What is the color of the drug?

b) What is the name of the drug?

c) Picking a drug that's effective against the bug, that you can get to the location where the problem is, and that the patient can tolerate

d) What is the price of the drug?

c) Picking a drug that's effective against the bug, that you can get to the location where the problem is, and that the patient can tolerate