Term
The ability of a drug to injure a target cell or 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: narrow-spectrum antibiotics broad- spectrum antibiotics |
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Definition
narrow-spectrum antibiotics – are active against only a few species of microorganisms broad- spectrum antibiotics –are active against a wide variety of microbes
narrow-spectrum drugs are generally preferred to broad-spectrum drugs |
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| v List the three major groups used to classify antimicrobial drugs according to susceptible organisms. |
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Definition
| Antibacterial drugs (mycobacterium tuberculosis, gram-negative aerobes, gram-positive cocci and gram positive bacilli) Antifungal drugs
Antiviral drugs (HIV, Influenza)
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v Over time, what may happen to an organism that had once been highly responsive to an antibiotic? Why is this a great concern? |
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Definition
| Over time, 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 develop. Acquired resistance is of great concern in that it can render currently effective drugs useless, thereby creating a clinical crisis and a constant need for new antimicrobial agents. |
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| v What or who becomes drug resistant, the microbe or 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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Definition
| 1. Microbes may elaborate drug-metabolizing enzymes. Through production of enzymes, some microorganisms are able to inactivate several different kinds of antibiotics. 2. Microbes may cease active uptake of certain drugs. Because the site of action of many antibiotics is intracellular, reduced drug uptake will cause resistance, This mechanism is responsible for some cases of resistance to tetracyclines. 3.Microbial drug receptors may undergo change, resulting in decreased antibiotic binding and action. For example, some bacteria are now resistant to streptomycin because of structural changes in bacterial ribosomes, the sites at which streptomycin acts to inhibit protein synthesis. 4. Microbes may synthesize compounds that antagonize drug actions.For example, by acquiring the ability to synthesize increased quantities of PABA, some bacteria have developed resistance to sulfonamides. |
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| v Explain the process that has lead to many bacteria being resistant to penicillin G. because of increased production of penicillinase, an enzyme that inactivates penicillin. Through production of enzymes, some microorganisms are able to inactivate several different kinds of antibiotics. |
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| v Read through the section “How Do Antibiotics Promote Resistance?” for understanding. (1) microbes secrete compounds that are toxic to other microbes, (2) microbes within a given ecologic niche (eg, large intestine, urogenital tract, skin) compete with one another for available nutrients Under drug-free conditions various microbes in a given niche keep one another in check. |
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v Which agents are more likely to promote resistance broad-spectrum or narrow-spectrum drugs antibiotics? All antimicrobial drugs promote the emergence of drug-resistant organisms. However, some agents are more likely to promote resistance than others. Because broad-spectrum antibiotics kill off more competing organisms than do narrow-spectrum drugs, broad-spectrum agents do the most to facilitate emergence of resistance
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| v Read through the section “Does the Amount of Antibiotic Use Influence the Emergence of Resistance?” for understanding. The more that antibiotics are used, the faster drug-resistant organisms will emerge. Not only do antibiotics promote emergence of resistant pathogens, they also promote overgrowth of normal flora that possess mechanisms for resistance. Because drug use can increase resistance in normal flora, and because normal flora can transfer resistance to pathogens, every effort should be made to avoid use of antibiotics by individuals who don’t actually need them (ie individuals who don’t have a treatable infection) |
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v Explain why nosocomial infections (defined as infections acquired in hospitals) are among the most difficult to treat.
Because hospitals are sites of intensive antibiotic use, resident organisms can be extremely drug resistant, As a result, nosocomial infections are among the most difficult to treat. |
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v Define suprainfection.
Is simply a special example of the emergence of drug resistance. A suprainfection is defined as a new infection that appears during the course of treatment for a primary infection. Suprainfections are caused by drug-resistant microbes, these infections are often difficult to treat.
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v 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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Definition
| Prevent infection Vaccinate, get the catheters out Diagnose and treat infection effectively Target the pathogen Access the experts Use Antimicrobials Wisely Practice antimicrobial control Use local data Treat infection, not contamination Treat infection, not colonization Know when to say “no” to vanco Stop treatment when infection is cured or unlikely Prevent Transmission Isolate the Pathogen Break the chain of contagion |
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| v What major cause of antibiotic resistance is not addressed in the CDC campaign? Feeding thousands of tons of antibiotics to livestock to promote growth |
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Definition
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| v Read through BOX 82-1: “Antibiotics in Animal Feed: Hastening Antibiotic Armageddon” |
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Definition
| Imposes a large threat: passage of resistance genes to normal intestinal flora, and then from normal flora to other human pathogens All antibiotics used in humans are used in animals Use of antibiotics by vegetable and fruit growers is just as widespread as in anaimal husbandry, and probably just as detrimental to public health |
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| v List examples of catheters and other invasive devices that are a site for nosocomial infections. What strategy can help prevent these infections? |
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Definition
| Catheters and other invasive devices are the leading exogenous cause of nosocomial infections. IV catheters, arterial catheters, urinary tract catheters, endotracheal tubes, and other devices. To help prevent these infections, catheters should be used only when essential, and should be removed as soon as they are no longer needed |
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| v Name two factors that must be determined in order to choose the proper antimicrobial therapy. Proper antimicrobial therapy requires that we choose drugs that are active against the causative organism. To do so, we must determine both the identity and drug sensitivity of the pathogen |
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| v Why is it so important to delay emergence of vancomycin-resistant organisms? Vancomycin is a drug of last resort against several important pathogens, including methicillin-resistant Staph. Aureus (MRSA) and multidrug-resistant Steptococcus pheumoniae. To delay emergence of bancmycin-resistant organisms, we must use the drug only when clearly necessary. |
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v What is one essential practice that will help break the chain of contagion? Wash your hands, before and after touching the patient
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v What is the therapeutic objective when treating infection?
The therapeutic objective is to produce maximal antimicrobial effects while causing minimal harm to the host. To achieve this goal, we must selec the most appropriate antibiotic for the individual patient. |
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Definition
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v When choosing an antibiotic, what three principal factors must be considered
1. The identity of the infecting organism2. Drug sensitivity of the infecting organism3. Host factors, such as the site of infection and the status of host defenses |
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| v What three factors contribute to a drug being considered a “drug of first choice” for a given infection? The drug of first choice may be preferred for several reasons, such as greater efficacy, lower toxicity, or more narrow spectrum |
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Definition
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| v Name three conditions that might rule out the use of a first-choice agent Allergy to the drug of choiceInability of the drug of choice to penetrate to the site of infectionUnusual susceptibility of the patient to toxicity of the first-choice drug |
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| v Optimally, what two pieces of information should be determined prior to the start of antimicrobial therapy? Optimal antimicrobial therapy requires identification of the infecting organism and determination of its drug sensitivity. |
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v When might treatment have to be initiated before test results are available? Generally, what type of drug is initially chosen?
When the patient has a severe infection, we may have to initiate treatment before test results are available Under these conditions, drug section must be based on clinical evaluation and knowledge of which microbes are most likely to cause infection at a particular site.
Broad-spectrum |
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| v What action is essential if conditions demand that therapy be started in the absence of laboratory data? Why? |
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Definition
When conditions demand that we start therapy in the absence of laboratory data, It is essential that samples of exudates and body fluids be obtained for culture prior to initiation of treatment; if antibiotic are present at the time of sampling, they can suppress microbial growth in culture, and can thereby confound identification.
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| v What is the first rule of antimicrobial therapy? To match the drug with the bug |
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Definition
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| v What should be done if treatment is begun in the absence of a definitive diagnosis? If treatment is begun in the absence of a definitive diagnosis, positive identification should be established as soon as possible, so as to permit adjustment of the regimen to better conform with the drug sensitivity of the infecting organism |
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| v List examples of sites where samples may be taken to identifying microorganisms. Samples for examination can be obtained from pus, sputum, urine, blood, and other body fluidsThe most useful samples are direct aspirates from the site of infection |
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| v What may be required in order to increase the small number of infecting organisms for positive identification? Under these conditions, positive identification may require that the microbes be grown out in culture. |
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| v When should cultures be taken? Material for culture should be obtained prior to initiating treatment |
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Definition
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| v What precautions should be taken when obtaining samples for microscopic examination or culture? The samples should be taken in a fashion that minimizes contamination with normal body flora.The samples should not be exposed to low temperature, antiseptics, or oxygen |
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| v 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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Definition
| Testing is indicated only when the infecting organism is one in which resistance is likely. Hence, for microbes such as the group A streptococci, which have remained highly susceptible to penicillin G, sensitivity testing is uncecessary In contrast, when resistance is common, as it is with Staph. aureus and the gram-negative bacilli, test for drug sensitivity should be performed |
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Term
v Define
Minimum inhibitory concentration (MIC) The lowest concentration of antibiotic that produces complete inhabitation of bacterial growth (but does not kill bacteria) |
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Definition
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Term
Define Minimum bactericidal concentration (MBC) The lowest concentration of drug that produces a 99.9% decline in the number of bacterial colonies (indicating bacterial kill)
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| v 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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Definition
| No, host defenses consist primarily of the immune system and phagocytic cells (macrophages, neurophils). Without the contribution of these defenses, successful antimicrobial therapy would be rare. In most cases, the drugs we use do not cure infection on their own. Rather, they work in concert with host defense systems to subdue infection. |
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| v Name three sites where drug penetration may be hampered, making it difficult to achieve the MIC. |
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Definition
Drug access can be impeded in meningitis (because of the blood-brain barrier), Endocarditis (because bacterial vegetations in the heart are difficult to penetrate), and Infected abscesses (because of poor vascularity and the presence of pus and other material)
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Term
v With what family of drugs are severe allergic reactions most common?
Penicillins |
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| v What is imperative regarding the duration of antibiotic therapy? What instructions should be provided to the patient? What does early withdrawal frequently cause? |
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Definition
It is imperative that antibiotics not be discontinued prematurely 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 Early withdrawal is a common cause of recurrent infection, and the organisms responsible for relapse are likely to be more drugs resistant than those present when therapy began
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| v List the three possible results when two antibiotics are used together. The result may be additive, potentiative, or, in certain cases, antagonistic |
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Definition
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v Define
Additive response Is one in which the antimicrobial effect of the combination is equal to the sum of the effects of the two drugs alone Potentiative (synergistic) interaction- (also called synergistic interaction)Is one in which the effect of the combination is greater than the sum of the effects of the individual agents
Antagonism- is most likely when a bacteriostatic agent (eg, tetracycline) is combined with a bactericidal drug (eg, penicillin). 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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| v What is most common indication for use of multiple antibiotics? Is initial therapy of severe infection of unknown etiology, especially in the neutropenic host. |
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| v Give an example of 2 antibiotics that may be combined to provide enhance antibacterial action. Penicillin plus an aminoglycoside in the treatment of enterococcal endocarditis |
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v Define antibiotic prophylaxis. the use of an antibiotic to protect a patient from an anticipated bacterial invasion associated with a medical or dental invasive procedure, particularly patients with a compromised cardiovascular system and risk of bacterial endocarditis. Are given to prevent infection rather than to treat an established infection
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| v Name 6 types of surgery when antimicrobial prophylaxis is both appropriate and effective. For this indication, when should antibiotics be administered? Cardiac surgery, peripheral vascular surgery Orthopedic surgery, surgery on the GI tract (stomach, duodenum, colon, rectum and appendix) Hysterectomy, An emergency cesarean section |
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| v When should individuals with congenital or valvular heart disease and those with prosthetic heart valves receive prophylactic antimicrobial medication to prevent bacterial endocarditis? Prior to surgery, dental procedures, and other procedures that may dislodge bacteria into the bloodstream |
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| v How well do the majority of viral infections respond to antimicrobial therapy? No benefit |
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| v Name two important clinical indicators of successful antimicrobial therapy. Reduction of fever and resolution of signs and symptoms related to the affected organ system (eg, improvement of breath sounds in patients with pneumonia) |
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| v Identify two reasons serum drug levels may be monitor during antimicrobial therapy. To ensure that levels are sufficient for antimicrobial effects and to avoid toxicity from excessive levels |
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| v What does the term selective toxicity refers to? The ability of a drug to injure invading microbes without injuring cells of the host |
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Definition
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| v What is the difference between narrow-spectrum and broad-spectrum antibiotics? Narrow-spectrum antibiotics are active against only a few microorganisms, whereas Broad spectrum antibiotics are active against a wide array of microbes |
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Definition
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| v What is the difference between bactericidal and bacteriostatic drugs? Bactericidal drugs kill bacteria, whereas bacteriostatic drugs only suppress growth |
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Definition
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| v Which antibiotics promote the emergence of resistance more? Emergence of resistance to antibiotics is a major concern in antimicrobial therapy |
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Definition
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Term
v What is required for effective antimicrobial therapy? Effective antimicrobial therapy requires that we determine both the identity and drug sensitivity of the infecting organism
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