Antibacterial Chemotherapy PDF

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Antibacterial Chemotherapy...

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Antibacterial Chemotherapy 1. Explain what is meant by selective toxicity. Selective toxicity refers to the ability of an antimicrobial drug to harm the pathogen without harming the host 2. Explain the difference between broad-spectrum and narrow spectrum antibiotics. Broad spectrum antibiotics have an effect on many pathogens, whereas narrow spectrum antibiotics only effect a few pathogens 3. What factors influence the effectiveness of antimicrobial drugs? (One mark each) - Bacterial susceptibility and resistance - Bacterial tolerance, persistence - If bacteria is found in a bio film - Inoculum size - Antimicrobial concentration. - Host factors (serum effect and impact on gut microbiota) 4. Describe four mechanisms of antibacterial drug actions with examples of the classes of antibiotics for each. (One mark each) Inhibition of cell wall synthesis  inhibit normal synthesis of peptidoglycan by bacteria and cause osmotic lysis (e.g., penicillin) Inhibition of protein synthesis  alter bacterial ribosomes interfering with translation causing fault protein synthesis (e.g., Erythromycin) Inhibition of nucleic acid synthesis  can black DNA replication by inhibiting DNA polymerase or DNA helicase or can black transcription by inhibiting RNA polymerase (e.g., Ciprofloxacin) Metabolic antagonism  act as antimetabolites by antagonising or blocking functioning of metabolic pathways by completely inhibiting the use of metabolites by key enzymes and are structural analogues which are structurally similar to and compete with naturally occurring metabolic intermediates and thus can block normal cellular metabolism (e.g., Trimethoprim) 5. How is the effectiveness of antimicrobial activity expressed? How is the effectiveness of antimicrobial activity determined? Effectiveness is expressed in two ways: Minimal inhibitory concentration. (MIC)  lowest concentration of drug that inhibits growth of the pathogen Minimal lethal concentration (MLC)  lowest concentration of drug that kills the pathogen Effectiveness is determined using tables that relate zone diameter to degree of microbial resistance

6. What attributes can be attributed to the ideal antimicrobial agent? - Solubility in body fluids - Selective toxicity - Toxicity not easily altered - Non allergenic - Stability - Resistance not easily acquired - Long shelf life - Reasonable cost 7. The therapeutic index is a measure used as an expression of selective toxicity. How is it defined? TI is a quantitively measurement of the relative safety of a drug. It is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxicity. It is calculated by : Toxic dose / therapeutic dose 8. What does a high therapeutic index indicate? A low TI means bad for bacteria, but also very bad for host A high TI means that the frug has targeted function and if very specific to a particular pathogen...