Antibacterial chemotherapy Quiz on antibiotics: penicillins, cephalosporins, aminoglycosides, tetracyclines, macrolides, and antimetabolites. The issue of resistance will also be covered. Matt2425 published on May 26, 20134 responses 0 Questions in vertical order What is the mechanism of action of trimethoprim? Inhibits dihydropteroate reductase and pyrimidine synthesis. Prevents synthesis of dihydrofolic acid Competes with para-amino benzoic acid for dihydrofolate reductase Prevents synthesis of tetrahydrofolic acid Regarding benzyl-penicillin, which statement is incorrect? Benzylpenicillin is active against most gram positive cocci and some gram negative bacteria. Phenoxylmethyl penicillin (POMP) is more potent than benzyl penicillin because it is more acid stable and orally active. Benzylpenicillin is susceptible to beta lactamases. Benzylpenicillin cannot be used to treat certain gram negative rods such as B. fragilis, Treponema, leptospira and actinomyces. Which of the following categories correctly pair the drug class with examples of the drug? Tetracyclines: erythromycin Macrolides: streptomycin Aminoglycosides: clarithromycin DNA Gyrase inhibitor: ciprofloxacin What are some side effects of penicillins? Select the three correct answers Joint effusions Spleen and lymph gland enlargement Liver damage Urticarial skin eruptions Which pair correctly describes the absorption of beta-lactamase resistant penicillins? Cloxacillin - well absorbed Flucloxacillin - variable absorption Methicillin - well absorbed Nafcillin - poorly absorbed Which of these statements is NOT correct regarding bacterial resistance to classical bacteriocidals (penicillin and cephalosporins)? Bacterial resistance can arise due to inhibition of penicillin binding proteins. Bacterial resistance can arise due to mutations in transpeptidases Bacterial resistance can arise due to increased beta-lactamase activity Bacterial resistance can arise due to the transfer of resistance genes via conjugative plasmids. What is the mechanism of action of tetracyclines? They inhibit the formation of the cell wall mediated by transpeptidases of peptidoglycan. They bind to mRNA and the ribosomal 30S subunit preventing binding of aminoacyl tRNA. They prevent mRNA translocating from the nucleus into the cytosol. They inhibit ribosomal 50S subunit preventing elongation of the peptide chain and moevement of the ribosome. Chloramphenicols have serious side effects that may preclude their clinical use. What are they? Hepatotoxicity Nephrotoxicity Ototoxicity Irreversible aplastic anaemia. What is an advantage of extended spectrum penicillins, such as carbenicillin, ticarbenicillin, azlocillin and pipercillin? They are resistant to beta-lactamase activity. They can act against pseudomonads. They are well absorbed orally. They are very effective against gram negative bacteria. Which statement best describes the administration of penicillin? They have long plasma half lives. Benzyl-penicillin is easily hydrolysed in the stomach so it is not clinically useful. Penicillins distribute well through body fluids and through the blood brain barrier. Clavulanic acid is often administered together with penicillins as a suicide substrate for beta lactamases. Regarding cephalosporins, which statement is NOT correct? Cephalosporins are generally administered orally. Some of them eg. cefoperazone, cefotaxime, cefuroxime, latamoxef can cross the blood brain barrier and so can treat meningitis. They are first choice drugs for treating gram negative rods of Enterobacteriaceae eg. E. Coli, enterobbacter and Klebsiella They have the same mechanism of action as penicillins. What are the differences between amoxycillin and ampicillin? Amoxycillin is resistant to beta lactamases produced by S. Aureus and many gram negative organisms. Amoxycillin can be delivered in pro-drug form, whereas ampicillin can not. Amoxycillin gives lower blood levels compared to ampicillin and causes more GI tract disturbances. Ampicillin is more prone to cause diarrhoea and GI tract disturbances.