Antibiotics

Question 1

Antibiotic classes

Answer 1

Cell wall inhibitors (penicillins, cephalosporins, glycopeptides)
Inhibitors of nuclear acid synthese (metronidazole)
Inhibitors of protein synthesis (aminoglycosides, macrolides, lincosamides, chloramphenicol, tetracyclines)
Inhibitors of metabolic pathways (folate synthesis inhibitors) (sulphonamides and trimethoprim)

Question 2

MOA penicillin G (benzylpenicillin) & V

Answer 2

B-lactams bind to PBPs (enzyme responsible for final stages of peptidoglycan synthesis. Peptidoglycans confer wall strength and rigidity, essential for cell wall formation), causing accumulation of cell wall precursors. This initiates production of autolytic enzymes & cell lysis.

Question 3

Spectrum of Penicillin G and V

Answer 3

Gram positives + Neisseria

Question 4

Mechanism of resistance to penicillins

Answer 4

B lactamase produced by staph aureus. Attaches to B lactam so it can no longer bind PBPs.

Question 5

Spectrum of Amoxicillin/Ampicillin

Answer 5

Essentially penicillin with altered side chains.
Gram positives + Neisseria, Haemophilus and E. Coli
(Side chain which allows it to get through porins of gram negatives)

Question 6

Adverse effects of penicillins

Answer 6

Hypersensitivity reactions common. Less common: anaphylaxis, nephritis.
These occur because penicillins can react with our own proteins and become antigenic.

Question 7

Drugs that overcome B-lactamase activity

Answer 7

Penicillin resistant SA: Dicloxacillin and Flucloxacillin

B lactamase inhibitors: clavulanic acid (administered as augmentin: clavulanic acid + amoxicillin)

Question 8

MOA Cephalosporins

Answer 8

B lactam antibiotics with similar structure to penicillins, with similar mode of action but cover broader range of bacterial infections

Question 9

Name a cephalosporin

Answer 9

Ceftriaxone

Question 10

ARx cephalosporins

Answer 10

Similar to penicillins: hypersensitivity (about 10% of those allergic to penicillin are also allergic to this), rash, overgrowth of other organisms, diarrhoea common (may be due to c. difficile)

Question 11

Name a glycopeptide

Answer 11

Vancomycin

Question 12

MOA of glycopeptides

Answer 12

Inhibit cell wall synthesis of gram positives only (no action against gram -ve) by interfering with cell wall synthesis, binding to D-alanine-D-alanine ends of the peptide chain

Question 13

Indication for glycopeptides

Answer 13

Reserved for serious infections where other treatments have failed (e.g. MRSA, MRS epidermatidis, those who are sensitive to penicillin and clostridium and c. difficile, which causes pseudomembranous colitis).

Question 14

Treatment for helicobacter pylori

Answer 14

2 antibiotics: usually metronizadole and a penicillin plus proton pump inhibitor

Question 15

Name a nucleic acid synthesis inhibitor

Answer 15

Metronidazole

Question 16

What class does metronidazole belong to

Answer 16

Nucleic acid synthesis inhibitors

Question 17

Uses of metronidazole

Answer 17

Aerobic bacteria (e.g. clostridium), aerobic protozoa (e.g. giardia), helicobacter pylori (used with penicillin and proton pump inhibitor)

Question 18

Mechanism of action of metronidazole

Answer 18

Nitro group of metronidazole is reduced as it accepts electrons; its reduced intermediate products damage DNA and inhibit replication.

Question 19

Mechanism of action of aminoglycosides

Answer 19

Enters bacteria via active transport and binds to 30S ribosome subunit, freezing it so no more protein can be produced.

Question 20

Name an aminoglycoside

Answer 20

Gentamicin

Question 21

ARx of gentamicin

Answer 21

Ototoxicity and nephrotoxicity (narrow therapeutic range(

Question 22

Mechanisms of resistance to aminoglycosides

Answer 22

Target site alteration, alteration of cell wall permeability, aminoglycoside-modifying enzymes, which the bacteria may produce

Question 23

Name three macrolides

Answer 23

Erythromycin (most commonly used for the treatment of stap and strep when hypersensitivity is a problem), clarithromycin (most commonly used against gram +ve bacteria), azithromycin (less active against gram positive organisms)

Question 24

What class are erythromycin and azithromycin

Answer 24

Macrolides (inhibitors of protein synthesis)

Question 25

Spectrum of activity

Answer 25

Wide - gram +ve cocci, chlamidya, anaerobes

Question 26

Most commonly used for treatment of staph and strep when hypersensitivity is a problem

Answer 26

Erythromicin

Question 27

Types of protein synthesis inhibitors

Answer 27

aminoglycosides, macrolides, lincosamides, chloramphenicol, tetracylines

Question 28

Mechanism of action of macrolides

Answer 28

Inhibits protein synthesis by binding to the 50S subunit of the ribosome, inhibiting enzyme peptidyl-transferase, prevents transfer of the peptidyl tRNA from the A-site to the P-site, and thus inhibits protein synthesis

Question 29

Resistance to macrolides

Answer 29

alteration of the target ribosome site and efflux of the drug from the cell

Question 30

ARx Macrolides

Answer 30

nausea, upper GIT discomfort, and infrequently, deafness

and jaundice.

Question 31

MOA lincosamides

Answer 31

Similar to macrolides in that they inhibit peptide bond formation.

Question 32

Lincosamides spectrum of activity

Answer 32

gram positive aerobes and most anaerobes (broad spectrum).

Question 33

Indication for lincosamides

Answer 33

Not used first up (it is 2nd line therapy in people who cannot handle conventional
therapy or where resistance is of concern). The more use an antibiotic has, the more
resistance bacterium become.

Question 34

ARx for lincosamides

Answer 34

Antimicrobial associated diarrhoea

Question 35

Tetracycline spectrum of activity

Answer 35

very broad spectrum of effects, on gram-positive, negative intracellular pathogens and mycoplasma (cell wall deficient bacteria). They tend to be bacteriostatic, not cidal.

Question 36

MOA tetracyclines and examples

Answer 36

TETRACYCLINE & DOXYCYCLINE
They bind to the 30S subunit, distorts it such that anticodons of tRNAs cannot align properly with the codons of mRNA, inhibiting protein synthesis

Question 37

Resistance to tetracylines

Answer 37

Resistance occurs because tetracyclins are widely used, and now many bacterial strains can produce efflux pumps to pump the antibiotic out.

Question 38

ARx of tetracyclines

Answer 38

GIT intolerance (pain and diarrhoea), candidiasis due to overgrowth of normal flora, and interferes with bone development and browning of teeth.

Question 39

CI for tetracylines

Answer 39

Contraindicated in those <8 years old and in pregnancy.

Question 40

Name two inhibitors of metabolic pathways/folate synthesis inhibitors

Answer 40

sulphonamides (previously used for UTIs. No longer used due to toxicity) and trimethoprim

Question 41

MOA trimethoprim

Answer 41

broad spectrum bacteriacidal agent which inhibits dihydrofolate reductase and thus inhibits folate synthesis in bacteria (folate is necessary for DNA and RNA synthesis)

Question 42

Major use of trimethoprim

Answer 42

UTI’s with limited toxicity (but cannot use it during pregnancy)

Question 43

Minimal Inhibitory Concentration (MIC)

Answer 43

the lowest concentration of an antibiotic which will inhibit the growth of a microorganism.

Question 44

Minimal Bacteriocidal Concentration (MBC)

Answer 44

the lowest concentration of an antibiotic which will kill a microorganism.

Question 45

Clinical uses of trimethoprim

Answer 45

Used on its on in UTI and respiratory tract infections, and with sulfonamides for p. jirovecii, which causes pneumonia in patients with AIDS

Question 46

Clinical uses of penicillin

Answer 46

Depending on sensitivity testing:

• BENZYLPENICILLIN: Bacterial meningitis (caused by Neisseria meningitidis, streptococcus pneumoniae)
• FLUCLOX: bone and joint infections (e.g. with staph aureus)
• OTITIS MEDIA (organisms commonly include strep pyogenes and h. influezae): AMOXI