1 Intro to antibacterial agents Flashcards
Differentiate between antibiotics and antimicrobial agents
Antibiotics are organically produced by bacteria.
Antimicrobials are antibiotics/synthetic/semi-synthetic compounds that kill organisms.
Differentiate between bacteriostatic and bactericidal
Bacteriostatic: inhibits bacterial growth through protein synthesis.
Bactericidal: kills bacteria (cell wall-active agents)
Define MIC
Minimum inhibitory concentration: minimum conc of antibiotic at which visible growth is inhibited
What is the structure of a bacterial cell wall?
Made of peptidoglycans. These are polymers of NAM (n-acetyl muramic acid) and NAG (N-acetly glucosamine). These are cross-linked by Gly5. Terminal D-ala is lost on cross linking
What types of antibiotics are cell wall synthesis inhibitors?
Beta-lactams.
Glycopeptides.
What is the structure of B-lactams and how do they work?
Beta lactam ring is analogue of D-alanyl-D-alanine.
Interferes with penicillin binding proteins that cross link peptidoglycans in bacterial cell wall.
Name the four classes of beta-lactams.
Penicillins.
Cephalosporins.
Carbapenems.
Monobactams.
Explain how glycopeptides work, give one example and explain their activity limitations.
Bind to D-alanyl-Dalanine on NAM, inhibiting cross-linking.
Vancomycin.
Only act on gram+ves as unable to penetrate outer membrane porins.
How is protein synthesised in bacteria?
Ribocnucleotin complexes catalyse peptide bond formation and synthesise polypeptides.
50S and 30S units join to form 70S initiation complex.
Name the four classes of protein synthesis inhibitors.
Aminoglycosides.
Macrolide’s, Lincosamides, Sterptomycins.
Tetracyclines.
Oxazolidinones
How do aminoglycosides work? 1 example.
Bind to 30S. Gentamicin.
How do MLS antibiotics work?
Bind to 50S and block exit tunnel.
How do tetracyclines work? 1 example.
Bind to 30S and interfere with tRNA binding. Inhibit RNA translation.
Doxytetracycline.
How do oxazolidinone work? 1 example.
Binds to 50S preventing 70S formation.
Linezolid.
Name the two types of DNA synthesis inhibitors.
Trimethoprim and sulphonamides.
Quinolones and fluoroquinolones.
What is co-tramoxizole and how does it work?
Sulphonamides and trimethoprim. Inhibit folate synthesis.
How do quinolones and fluoroquinolones work?
Inhibit DNA gyrase and topoisomerase IV. Preventing DNA supercoiling.
What is rifampicin and how does it work?
RNA polymerase inhibitor.
Prevents mRNA synthesis.
What is daptomycin and how does it work?
Cyclic lipopeptide. Inserts lipophilic tail into membrane, depolarising it.
What are the specific adverse effects of ahminoglycosides, beta-lactams and linezolid?
Amino- reversible renal impairment.
Beta- allergic reactions.
Linezolid - bone marrow depression
Which antibiotics are safe to use in penicillin allergy?
Non-severe: cephalosporins and carbapenems.
Any: aztreonam
Which antibiotics commonly precipitate a C.diff infection?
Cephalosporins.
Ciprofloxacin.
Clindamycin.
What is empiric therapy?
Best guess at antibiotics based on local policies and predicted susceptibility.
Which antibiotics have good availability in CSF?
Beta lactams.
Which antibiotics have good availability in urine?
Trimethoprim.
Beta-lactams.
What are the pharmacodynamic considerations for antibiotic prescription?
Conc dependant. Intermittent high dose. Amino glycosides.
Time dependant. Frequent dose. Beta-lactams
Which synergistic combination of antibiotics is used for streptococcal endocarditis?
B lactams and aminoglycosides.
Name a cephalosporin.
Cefuroxime.
Name a carbapenem.
Meroprenem.
Name a monobactam.
What is it’s activity limitation?
Aztreonam.
Gram -ve only.
Two examples of MLS antibiotics.
Erythromycin. Clindamycin.
Name a quinolone.
Ciprofloxacin.
Which antibiotics have poor availability in CSF?
Aminoglycosides.
Vancomycin.
Which antibiotics have poor availability in urine?
MLS.
What is the spectrum of activity of daptomycin?
Only effective in g+ves.
How does trimethoprim work?
Binds to dihydrofolate reductase - preventing folate synthesis.
How do sulfonamides work?
Binds to dihydropteroate synthetase - preventing folate synthesis.
What type of allergic reactions can β-lactams cause?
Intolerance: nausea, diarrhoea.
Minor skin rash.
Anaphylaxis, urticaria, angio-oedema, bronchospasm, Stevens-Johnson syndrome.
What is flucloxacillin commonly used for?
Staph aureus.
What is benzylpenicillin commonly used for?
Strep pyogenes.
What are cephalosporins commonly used for?
Gram -ve bacilli.
What is vancomycin commonly used for?
Gram positives (MRSA).
What is metronidazole commonly used for?
Anaerobes.
