Module 6 Section 1 (Antimicrobials)

Question 1

Human infections are caused by four categories of microorganisms. What are they?

Answer 1

Bacteria, viruses, fungi, and parasites.

Question 2

Antimicrobials can be further classified depending on which of these four microorganisms they target. What are they?

Answer 2

Antibiotics, antivirals, antifungals, and antiparasitics, respectively.

Question 3

What is an antimicrobial?

Answer 3

In general, an antimicrobial is a chemical substance that impairs the growth and/or survival of microbes. These substances are often produced by another microorganism.

Question 4

Discuss the importance of antimicrobial therapy.

Answer 4

Antimicrobial molecules are viewed as ligands (drugs) where the receptors are microbial macromolecules.
- These targets are essential components of the biochemical reactions in the microbe and interference in these pathways kills the microbe.

Therefore, in antimicrobial therapy, the relationship between drug concentration and effect on a population of organisms is often expressed as an inhibitory sigmoid model, where E is effect as measured by microbial burden.

Question 5

True or false: Humans can acquire many different types of infections, and the pathogen responsible may cause infection in specific organs. Therefore, in choosing an antimicrobial agent to treat the infection, an important consideration is whether the drug can penetrate to the site of infection.

Answer 5

True

Question 6

Antibiotics are often administered orally, far away from the sites of infection. Why is this?

Answer 6

The penetration of a drug into an anatomical compartment depends on specific factors. Generally, the poorer the penetration of the antimicrobial into the anatomical compartment, the higher the likelihood of treatment failure.

Question 7

What factors affect the penetration of a drug into an anatomical compartment?

Answer 7

• Physical barriers that the drug must traverse (i.e. cell membranes). The greater the lipophilicity of a drug, the greater the likelihood that it will cross cell membranes
• Chemical properties of the drug
• Presence of transporters

Question 8

The microbiology lab plays a key role in determining the microbial responsible for an infection, and hence guiding the decision of which antimicrobial drug to use. The microbiology lab plays two roles. What are they?

Answer 8

1) To isolate and identify the culprit organism. Once the microbial species causing the infection has been identified, an informed decision of the class of antimicrobials likely to work in the patient can be made.

2) To perform susceptibility testing. This helps identify microbial resistance to the drugs, further defining which antimicrobial therapy should have the best success in eradicating the infection.
- Although susceptibility testing is central to decision making, it doesn’t completely predict patient response (a dose of drug by itself is a poor measure of drug exposure).
- Actual drug concentration achieved at the site of infection is the important measure.

Question 9

Antimicrobial therapy can be used in five different ways. What are they?

Answer 9

1) Prophylaxis: treating patients who are not yet infected. The goal of prophylactic treatment is to prevent infections.
- This is commonly used in immunosuppressed patients (e.g. transplant patients)

2) Preemptive: early targeted therapy in high-risk patients who have no symptoms of being infected, but have a test indicating that they do have an infection.

3) Empiric: patients have symptoms of an infection and need to be started on therapy before lab testing can be completed.
- In other words, it is too risky to wait for lab testing prior to beginning treatment.
- Starting empirical antimicrobial therapy relies on the clinical presentation and clinical experience.
- Performance of cultures is still mandatory, and therapy is modified after the fact, if required.

4) Definitive: the pathogen has been isolated and identified.
- The antimicrobial therapy can be streamlined to target the specific pathogen.
- Monotherapy is preferred to decrease toxicity and resistance.
- Combination therapy is an exception rather than a rule.

5) Suppressive: post treatment suppressive therapy.
- The infection is controlled, but not completed eradicated by the first round of treatment.
- Therapy is continued at a lower dose.