Antimicrobial Therapy Test Questions – Flashcards
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• Define selective toxicity.
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o The ability of a drug to injure a target organism without injuring other cells or organisms that are in intimate contact with the target
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• Define the following two terms used to classify antibiotics according to their antimicrobial activity:
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o Narrow-spectrum antibiotics: Active against only a few species of microorganisms o Broad-spectrum antibiotics: Active against a wide variety of microbes
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• List the three major groups used to classify antimicrobial drugs according to susceptible organisms.
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-Antibacterial -Antiviral -Antifungal
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• An antimicrobial medication that has selective toxicity has which of these characteristics?
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No injury occurring to the cells of the host
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• Over time, what may happen to an organism that had once been highly responsive to an antibiotic? Why is this a great concern? What or who becomes drug resistant, the microbe or the patient?
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o An organism that had once been highly responsive to an antibiotic may become less susceptible, or it may lose drug sensitivity entirely. In some cases, resistance to several drugs develops. o It is a great concern because it can render currently effective drugs useless, thereby creating a clinical crisis and a constant need for new antimicrobial agents. o The MICROBE becomes drug resistant, NOT the patient
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• List four ways that microbes become drug resistant because of alterations in their function or structure.
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o 1) Decrease the concentration of a drug at its site of action o 2) Inactivate a drug o 3) Alter the structure of drug target molecules o 4) Produce a drug antagonist
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• Explain the process that has lead to many bacteria being resistant to penicillin G.
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o Many bacteria are now resistant to penicillin G because of increased production of penicillinase, an enzyme that inactivates penicillin. Through production of enzymes, some bacteria can inactivate several different kinds of antibiotics.
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• Read through the section "How Do Antibiotics Promote Resistance?" for understanding.
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p. 973
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• Which agents are more likely to promote resistance, broad-spectrum or narrow-spectrum drugs antibiotics?
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o Broad-spectrum agents do the most to facilitate emergency of resistance Because broad-spectrum antibiotics kill more competing organisms than do narrow-spectrum drugs
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• Read through the section "Does the Amount of Antibiotic Use Influence the Emergence of Resistance?" for understanding.
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o YES! The more that antibiotics are used, the faster drug-resistant organisms will emerge. P. 974
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• Explain why nosocomial infections (defined as infections acquired in hospitals) are among the most difficult to treat.
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o Because hospitals are sites of intensive antibiotic use, resident organisms can be extremely drug resistant.
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Define suprainfection
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o A special example of the emergence of drug resistance o A new infection that appears during the course of treatment for a primary infection. o New infections develop when antibiotics eliminate the inhibitory influence of normal flora, thereby allowing second infectious agent to flourish.
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• Which of these conditions results when the normal flora is disturbed during antibiotic therapy?
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Superinfection (suprainfection)
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• List the four major strategies used in the CDC's Campaign to Prevent Antimicrobial Resistance to categorize 12 action steps for hospitals to take to Delay the Emergence of Resistance
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o Prevent infection o Diagnose and treat infection effectively o Use antimicrobials wisely o Prevent transmission
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• What major cause of antibiotic resistance is not addressed in the CDC campaign? Read through BOX 82-1: "Antibiotics in Animal Feed: Hastening Antibiotic Armageddon"
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o Feeding thousands of tons of antibiotics to livestock to promote growth. o Antibiotics are employed extensively in the livestock and poultry industries. Not surprisingly, this practice has created a large reservoir of drug-resistant bacteria, some of which now infect humans. In addition to being a direct detriment to health, these infections pose an even larger threat: passage of resistance genes to normal intestinal flora, and then from normal flora to other human pathogens.
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• Name two factors that must be determined in order to choose the proper antimicrobial therapy.
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o 1) The identity of the infecting organism o 2) Drug sensitivity o 3) Host factors, such as the site of infection and the status of host defenses
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• Why is it so important to delay emergence of vancomycin-resistant organisms?
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o It is a drug of last resort against several important pathogens, including methicillin-resistant Staph. Aureus and multidrug-resistant. Staph. Aureus and multidrug-resistant Streptococcus pneumonia. To delay emergence of vancomycin-resistant organisms, we must use the drug only when clearly necessary.
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• What is one essential practice that will help break the chain of contagion?
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WASH YOUR HANDS before and after touching any patient
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• What is the therapeutic objective when treating infection? When choosing an antibiotic, what three principal factors must be considered?
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o To produce maximal antimicrobial effects while causing minimal harm to the host. o 1) The identity of the infecting organism o 2) Drug sensitivity of the infecting organism o 3) Host factors, such as the site of infection and the status of host defenses
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• What three factors contribute to a drug being considered a "drug of first choice" for a given infection? Name three conditions that might rule out the use of a first-choice agent
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o Three factors that contribute to a drug being considered a "drug of first choice": Greater efficacy Lower toxicity More narrow spectrum o 1) Allergy to the drug of choice o 2) Inability of the drug of choice to penetrate to the site of infection o 3) Unusual susceptibility of the patient to toxicity of the first-choice drug
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• Optimally, what two pieces of information should be determined prior to the start of antimicrobial therapy?
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o Identification of the infecting organism o Determination of its drug sensitivity
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• When might treatment have to be initiated before test results are available? Generally, what type of drug is initially chosen?
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o When the patient has a severe infection o Broad-spectrum agent (once the identity and drug sensitivity of the infecting organism have been determined, we can switch to a more selective antibiotic)
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• What action is essential if conditions demand that therapy be started in the absence of laboratory data? Why?
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o It is essential that samples of exudates and body fluids be obtained for culture prior to initiation of treatment if antibiotics are present at the time of sampling, they can suppress microbial growth in culture, and can thereby confound identification
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• What is the first rule of antimicrobial therapy? What should be done if treatment is begun in the absence of a definitive diagnosis?
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o Match the drug with the bug o Positive identification should be established as soon as possible, so as to permit adjustment of the regiment to better conform with the drug sensitivity of the infecting organism
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• List examples of sites where samples may be taken to identifying microorganisms.
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o The quickest, simplest, and most versatile technique for identifying microorganisms is microscopic examination of a Gram-stained preparation. o Samples for exam can be obtained from pus, sputum, urine, blood, and other body fluids.
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• What may be required in order to increase the small number of infecting organisms for positive identification?
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o Positive identification may require that the microbes be grown out in culture.
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• When should cultures be taken? What precautions should be taken when obtaining samples for microscopic examination or culture?
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o Material for culture should be obtained prior to initiating treatment. Furthermore, the samples should be taken in a fashion that minimizes contamination with normal body flora. o The samples should not be exposed to low temperature, antiseptics, or oxygen
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• When testing for drug sensitivity is necessary, what types of tests are conducted? Just briefly summarize the basic information provided by the tests.
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o Disk-Diffusion Test (Kirby-Bauer test) This test is performed by inoculating an agar plate with the infecting organism and then placing on that plate several small disks, each of which is impregnated with a different antibiotic. o Broth Dilution Procedure Bacteria are grown in a series of tubes containing different concentrations of an antibiotic. The advantage is that this is more precise than disk-diffusion test Two clinically useful values: Minimum inhibitory concentration The lowest concentration of antibiotic that produces complete inhibition of bacterial growth (but doesn't kill bacteria) Minimum concentration Lowest concentration of drug that produces a 99.9% decline in # of bacterial colonies (indicating bacterial kill)
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• Do the antibiotics used in therapy cure the infection on their own? What part do host defenses play in the eradication of an infection?
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o The drugs we use do not cure infection on their own. Rather, they work in concert with host defense systems to subdue infection. o The goal of antibiotic treatment is to suppress microbial growth to the point at which the balance is tipped in favor of the host o Underscoring the critical role of host defenses is the grim fact that people whose defense are impaired, such as those with AIDS and those undergoing cancer chemotherapy, frequently die from infections that drugs alone are unable to control.
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• Name three sites where drug penetration may be hampered, making it difficult to achieve the minimum inhibitory concentration (MIC).
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o Drug access can be impeded in: Meningitis (because of the blood-brain barrier) Endocarditis (because bacterial vegetations in the heart are difficult to penetrate) Infected abscesses (because of poor vascularity and the presence of pus and other material)
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• With what family of drugs are severe allergic reactions are most common?
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Penicillins
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• What is imperative regarding the duration of antibiotic therapy?
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o It is imperative that antibiotics not be discontinued prematurely.
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• What instructions should be provided to the patient?
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o Patients should be instructed to take their medication for the entire prescribed course, even though symptoms may subside before the full course has been completed.
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• What does early withdrawal frequently cause?
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o It is a common cause of recurrent infection, and the organisms responsible for relapse are likely to be more drug resistant than those present when therapy began
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• List the three possible results when two antibiotics are used together.
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o Additive, potentiative, or antagonistic
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Definition of additive response
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One in which the antimicrobial effect of the combination is equal to the sum of the effects of the two drugs alone.
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Define potentiative (synergistic) interaction
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One in which the effect of the combination is greater than the sum of the effects of the individual agents.
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Define antagonism
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Most likely when a bacteriostatic agent is combined with a bactericidal drug. Antagonism occurs because bactericidal drugs are usually effective only against organisms that are actively growing. Hence, when bacterial growth has been suppressed by a bacteriostatic drug, the effects of a bactericidal agent can be reduced.
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• What is most common indication for use of multiple antibiotics?
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o Initial therapy of severe infection of unknown etiology, especially in the neutropenic host
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• Give examples of 2 antibiotics that may be combined to provide enhance antibacterial action.
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o Combined use of penicillin plus an aminoglycoside in the treatment of enterococcal endocarditis. Penicillin acts to weaken the bacterial cell wall: the aminoglycoside acts to suppress protein synthesis. The combination has enhanced antibacterial action because, by weakening the cell wall, penicillin facilitates penetration of aminoglycoside to its intracellular site of action
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Define antibiotic prophylaxis
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o These agents are given to prevent infection rather than to treat an established infection. o Much of this prophylactic use is uncalled for, but the benefits must be weighed against the risk of toxicity, allergic reactions, suprainfection, and selection of drug resistant organisms.
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• Name 6 types of surgery when antimicrobial prophylaxis is both appropriate and effective. For this indication, when should antibiotics be administered?
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o Surgery: Cardiac surgery Peripheral vascular surgery Orthopedic surgery Surgery on the GI tract (stomach, duodenum, colon, rectum, and appendix) Women undergoing a hysterectomy (a surgical operation to remove all or part of the uterus. In "dirty" surgery (operations performed on perforated abdominal organs, compound fractures, or lacerations from animal bites) Risk of infection is nearly 100%, so it is considered treatment, not prophylaxis o Should be administered before surgery, NOT after. A first-generation cephalosporin will suffice. o If procedure is unusually long, re-administration during surgery may be indicated. o Also, antimicrobial prophylaxis is appropriate in bacterial endocarditis, neutropenia (low levels of neutrophils in blood that leads to infection), and UTI infections that are REOCCURRING.
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• When should individuals with congenital or valvular heart disease and those with prosthetic heart valves receive prophylactic antimicrobial medication to prevent bacterial endocarditis?
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o Prior to undergoing procedure, these patients need prophylactic antimicrobial medication.
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• How well do the majority of viral infections response to antimicrobial therapy?
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o They DO NOT respond to currently available drugs (viral infections like mumps, chickenpox, and the common cold)
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• Misuse of antimicrobial drugs:
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o Attempted treatment of untreatable infection o Treatment of fever of unknown origin o Improper dosage o Treatment in the absence of adequate bacteriologic information o Omission of surgical drainage (surgical drainage and cleansing should be performed to promote antimicrobial effects)
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• Name two important clinical indicators of successful antimicrobial therapy.
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o Reduction of fever and resolution of signs and symptoms related to the affected organ system (Ex: improvement of breath sounds in patients with pneumonia)
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• Identify two reasons serum drug levels may be monitored during antimicrobial therapy.
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o Ensure that levels are sufficient for antimicrobial effects and to avoid toxicity from excessive levels.
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Which of these are examples of the improper use of antimicrobial medication? Select all that apply.
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-Treating an untreatable infection, such as sinusitis -Fever in a patient who has an immune deficiency
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A nurse should recognize that antibiotic prophylaxis would be appropriate in patients who have which of these medical conditions? Select all that apply.
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-Aortic valve replacement and neutropenia
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• What does the term selective toxicity refers to?
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o The ability of a drug to injure a target organism without injuring other cells or organisms that are in intimate contact with the target
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• What is the difference between narrow-spectrum and broad-spectrum antibiotics?
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o Narrow-spectrum antibiotics: Active against only a few species of microorganisms o Broad-spectrum antibiotics: Active against a wide variety of microbes
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• What is the difference between bactericidal and bacteriostatic drugs?
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o Bactericidal: Directly lethal to bacteria at clinically achievable concentrations o Bacteriostatic: Can slow the bacterial growth but do not cause cell death
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• Which antibiotics promote the emergence of resistance more?
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o 1) Tetracycline (1%) o 2) Amoxicillin (3%) o 3) Clarithromycin (10%) o 4) Metronidazole (40%) o 5) Tinidazole (40%)
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• What is required for effective antimicrobial therapy?
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o Match the drug with the bug o Prior to the start of antimicrobial therapy: Identification of the infecting organism Determination of its drug sensitivity
