9. Antimicrobial Agents Flashcards
What is the unique property of antimicrobials?
They ideally have no direct effect on the patient.
What are the three main targets of antibiotics?
DNA synthesis, protein synthesis, cell wall synthesis.
Which groups of antibiotics target DNA synthesis? Give an example of each.
Quinolones - ciprofloxacin. Folic acid antagonists - trimethoprim, sulphonamides.
Which groups of antibiotics target protein synthesis? Give an example of each.
Aminoglycosides - gentamicin. Macrolides - erythromicin. Tetracyclines - tetracycline.
Which groups of antibiotics target cell wall synthesis? Give an example of each.
Beta-lactams - penicillins, cephalosporins, carbapenems. Glycopeptides - vancomycin.
What are the two good reasons for using antibiotics?
Prevention of infections, and therapy of significant bacterial infections.
Which three groups of people should be given antibiotic prophylaxis?
Perioperative, short term (e.g. meningitis contacts), long term (e.g. aplenia, immunodeficiency).
What should the approach to antimicrobial treatment of significant bacterial infections be?
Treat culture proven infection but treat empirically if suspected infection.
What should be considered in empiric use of antibiotics?
What the likely cause of infection is, which antibiotics are likely to be effective, which effective antibiotic is the best choice.
Why must empiric treatment be considered in acutely ill patients?
Culture results can take 24-72 hours to get back and in that time, the patient may have seriously deteriorated.
What factors should be considered when trying to identify the likely cause of an infection?
Duration of illness, past medical history, occupational history, travel history, time of year, age, personal background, anatomical site.
What should be considered when trying to identify which antibiotics are likely to be considered?
Likely susceptibility and consequence of wrong choice - severity of infection, immune status of patient, baseline rate of resistance, community or healthcare onset.
What should be considered when trying to decide which effective antibiotic should be used?
Cost, efficacy, administration route, safety - age/toxicity/drug interaction/allergies/pregnancy/breast feeding/organ function.
What are the two outcomes of an ideal antibiotic therapy?
No effect on patient but clean kill of infecting bacteria (no resistance and minimal impact on non-target commensal organisms).
What are the ADRs of antibiotics?
Pharmacological - toxicities, drug interactions; allergic reaction; impact on normal flora.
What is therapeutic drug monitoring used to ensure?
Adequate dose and non-toxic dose.
Which antibiotic class is drug monitoring used for?
Aminoglycosides.
How can antibiotic sensitivity be measured?
Disc sensitivity.
What are the types of genetic basis of antibiotic resistance?
Chromosomal gene mutation, and horizontal gene transfer.
Explain chromosomal gene mutation.
Mutated gene conferring resistance is selected with antibiotic use as the non-mutated types are cleared and it proliferates.
Explain horizontal gene transfer.
Plasmids with gene for resistance are spread between bacteria.
What are the four main forms of antibiotic resistance?
Antibiotic inactivation, alteration of target site, alteration of metabolic pathways, reduced intracellular antibiotic accumulation.
Give an example of resistance by antibiotic inactivation.
Beta-lactamase.
Give an example of resistance by altered target site.
Penicillin binding protein.
Give an example of resistance by altered metabolic pathways.
Folic acid used instead of para-aminobenzoic acid.
Give an example of resistance by reduced intracellular antibiotic accumulation.
Active efflux mechanisms or decreased permeability.
How can antibiotic resistance be prevented?
Antimicrobial stewardship and infection control.
What are the rules of antimicrobial stewardship?
Right antibiotic at the right time at the right dose, frequency, and duration via the right route.
What is meant by time dependent or concentration dependent killing in successful treatment using antimicrobials?
Time - successful treatment needs prolonged antibiotic presence at site of infection but not at high concentrations.
Concentrations - successful treatment requires high antibiotic concentration at site of infection but not for a long time.
How can infection control decrease antibiotic resistance?
Prevent exposure to antibiotics - minimise risk of infection, monitor and control antibiotic prescribing. Prevent spread of resistant bacteria - isolation or cohorting, hand hygiene, decolonisation of patients.
