Pharmacology of antibiotics

Question 1

What are the bacterial targets of antimicrobial chemotherapy?

Answer 1

Bacterial cell wall, ribosomes, folate metabolism (part of DNA building blocks), DNA gyrases - affects how DNA functions (supercoiling)

Question 2

Amoxicillin, benzylpenicillin, fluoxacillin are all types of what?

Answer 2

Penicillin

Question 3

What type of antibiotic is penicillin?

Answer 3

beta-lactam antibiotic - contains beta-lactam ring

Question 4

Give the mechanism of penicillin

Answer 4

Targets cell wall synthesis by irreversibly binding to a TRANSPEPTIDASE - which cross links peptidoglycans in the cell wall.
Only effective in dividing organisms

Question 5

What are beta-lactamases?

Answer 5

Can inactivated by beta-lactamases secreted by resistant bacteria

Question 6

How are people allergic to penicillin?

Answer 6

Anaphylaxis - body produces antibodies against penicillin to produce allergic response

Question 7

What are cephalosporins

Answer 7

Also beta-lactam antibiotics, act in a similar way to penicillin

Question 8

Give the mechanism for glycopeptides - vancomycin

Answer 8

Inhibit synthesis by inhibiting the growth of the peptidoglycan chain - for severe superbugs - largely BACTERICIDAL

Question 9

Give the mechanism for tetracyclines - doxycycline

Answer 9

Inhibit protein synthesis by binding to the 30S subunit of the bacterial ribosome and preventing tRNA from binding at the acceptor site - are BACTERIOSTATIC (just stop growth - not to give to pregnant women or children

Question 10

When would you use macrolides

Answer 10

When someone is penicillin allergic

Question 11

Give the mechanism for macrolides

Answer 11

Prevent the translocation of the 50S subunit of the bacterial ribosome along the mRNA - prevent protein synthesis - BACTERIOSTATIC

Question 12

Give the mechanism for aminoglycosides (gentamicin)

Answer 12

Bind irreversibly to the 30S subunit of ribosomes –> misreading of mRNA - BACTERICIDAL and used to manage Gram-negative bacteria
.Synergy w penicillins: breakdown of cell wall, increases uptake of aminoglycosides into cell wall.

Question 13

Give mechanisms of quinolones (norfloxacin)

Answer 13

Inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. FOR GRAM NEGATIVE - DNA gyrase - Inhibit the supercoiling of bacterial DNA - essential for repair and replication
FOR GRAM POSITIVE - topoisomerase IV , interferes with separation of DNA strands on replication

Question 14

What is the clinical problem with using quinolones?

Answer 14

Desired peak conc. to facilitate bacterial killing but a low , sub therapeutic trough conc is used to reduce the chances of toxicity

Question 15

Give mechanism for trimethoprim

Answer 15

Folate antagonist and inhibits bacterial dehydrate reductase - interferes w DNA synthesis in bacteria - BACTERIOSTATIC

Question 16

Give the mechanism for sulphonamides

Answer 16

Analogues of p-aminobenzoic acid (PABA) and inhibit the growth of bacteria by competitively inhibiting the enzyme dihydropteroate synthase (for synthesis of folate from PABA)- REDUCES AVAILABLITY OF DNA AND RNA PRECURSORS

Question 17

Give the mechanism for metronidazole

Answer 17

Damages helical structures of DNA, protein and cell membrane - for anaerobic bacteria (only antibiotic you cant have w an alcoholic drink)

Question 18

How do you select antibiotics?

Answer 18

Sensitivity of organisms, broad spectrum antibiotics, resistance, allergies, pharmacokinetics (IV for rapid effects), oral route, drug interactions