Antibiotics

Question 1

MoA of antibiotics that acting on cell wall synthesis

Answer 1

Inhibition of cell wall synthesis -> bacteria dies

Question 2

2 examples of classes of the antibiotics that act on cell wall synthesis

Answer 2

• Beta-lactams: Penicillins, Cephalosporins
• Glycopeptides: Bacitracin

Question 3

MoA of antibiotics disturb cell membrane

Answer 3

Antibiotic binds to the cell membrane ->altering its structure -> cell membrane becomes more permeable -> disruption of osmotic balance -> leakage of cellular molecules -> increase water uptake -> cell death

Question 4

(2) examples of classes of antimicrobials that ac by disruption of a cell membrane

Answer 4

Polymyxins and Polyenes (anti-fungal)

Question 5

(2) examples of antibiotics that act by preventing DNA from being synthesised

Answer 5

Examples: Quinolines, nalidixic acid

Question 6

Example of antibiotic that act by preventing of RNA being synthesised

Answer 6

Rifamycin

Question 7

Examples of antibiotics that disturb protein synthesis by targeting 50s unit of ribosome

Answer 7

50s subunit: Erythromycin, Chloramphenicol

Question 8

Examples of antibiotics that target protein synthesis at 30s unit of ribosome (2)

Answer 8

30s subunit: Tetracycline, Streptomycin

Question 9

General mechanism of action of protein synthesis inhibitors

Answer 9

Subunit targeted by an antibiotic -> disruption of

ribosomes -> bacteria unable to make proteins

-> bacteria can stay alive but is unable to do

anything

(Therefore these antibiotics are bacteriostatic -

prevent bacterial growth)

Question 10

Mechanism of action of inhibitors of folic acid metabolism

Answer 10

• bacteria metabolise PABA (precursor) -> foliate (folic acid)
• folic acid is essential for the synthesis of: thymine and adenine (2 out of 4 nucleic acids that make up DNA)

Antibiotics:

PABA cannot convert into folic acid -> prevent

DNA synthesis

Question 11

(2) examples of antibiotics that act as folic acid inhibitors

Answer 11

Sulphonamides, Trimethoprim

Question 12

Mechanism of action of beta-lactams

Answer 12

Beta-lactams = Penicillins

Mechanism of action: inhibit cell wall synthesis = bactericidal

Question 13

Mechanism of resistance to beta-lactams

Answer 13

Mechanism of resistance: production of beta - lactamases -> hydrolysis of beta - lactam -> antibiotic structure is broken -> drug inactivation

Question 14

What drugs can overcome resistance from beta-lactamases?

Answer 14

Co-amoxiclav and Tazocin

Can inhibit beta-lactamase so can overcome resistance -> however have little antimicrobial effect -> given in combination with amoxicillin and Pipercillin

• mixed spectrum: gram positive and gram negative

Question 15

MoA of cephalosporins

Answer 15

Cephalosporins = beta-lactams

MoA:inhibit cell wall synthesis = bactericidal

Question 16

MoA of Carbapenems

Answer 16

Carbopenems= beta-lactams

Mechanism of action: inhibit cell wall synthesis = bactericidal (like all beta-lactams)

Binding to penicillin-binding proteins -> inhibition of cell wall synthesis

Question 17

Use of carbapenems

Answer 17

• most stable beta-lactam -> broader spectrum of activity than penicillins and cephalosporins
• broad spectrum (action against gram positive and gram negative organisms)
• used against multi-drug resistant bacteria:
• does not work against: MRSA, Enterococci and Pseudomonas)
• last line of defence
• used in hospitalised patients

Question 18

Example of antibiotics (2) that belong to glycopeptides class

Answer 18

Vancomycin (used for MRSA) and Teicoplanin

Question 19

Use of glycopeptides antibiotics

Answer 19

• used only for gram positive bacteria
• very toxic -> used as last line of defence (for patients critically ill or those with beta-lactam allergies)
• narrow spectrum of action
• bacterocidal only against enterococci
• do not penetrate to CSF
• usually given by IV

Question 20

MoA of glycopeptides antibiotic

Answer 20

Glycopeptides e.g. Vancomycin, Teicoplanin

Mechanism: bind to amino-acid within the cell wall* -> preventing the addition of new peptidoglycan units

-> inhibition of peptidoglycan synthesis -> inhibition of cell wall synthesis

Question 21

Side effects (3) of Vancomycin use

Answer 21

• Red Man Syndrome - appears within 4 - 10 mins after administration of IV or after completion of infusion. Flushing, erythematous rash affecting face, neck and upper torso (as vancomycin mediate Ig- independent mast cell degranulation); Rx with antihistamines; symptoms less likely to occur with slow infusion (over at least 60 minutes)
• Ototoxicity (rare)
• Nephrotoxicity

Question 22

MoA of Aminoglycosides

Answer 22

Mechanism: act on 30s ribosomal unit -> block the initiation of translation -> misreading of mRNA

Examples: Gentamicin, Amikacin, Neomycin, Tobramycin

Question 23

Examples (4) of aminoglycosides

Answer 23

Examples: Gentamicin, Amikacin, Neomycin, Tobramycin

Question 24

Aminoglycosides

• use
• side effects

Answer 24

Examples: Gentamicin, Amikacin, Neomycin, Tobramycin

• Effective against: gram -ve (except Streptococci and enterococci) and gram +ve
• Side effects: Nephrotoxicity, Othotoxicity

Question 25

MoA of Tetracyclines

Answer 25

act on 30s ribosomal subunit -> block the attachment of tRNA to the ribosome

Question 26

• Use of Tetracyclines
• side effects

Answer 26

• Effective against: many gram +ve and -ve, some parasites
• Side effects: photosensitive rash, nausea, yellow teeth

Question 27

MoA of Macrolides

Answer 27

Mechanism: act on 50s subunit of a ribosome; prevent continuation of protein synthesis - bacteriostatic

Examples: Clarithromycin, Erythromycin

Question 28

Use of macrolides

Answer 28

Effective against: gram positive cocci, intracellular and anaerobes