Antibiotics I

Question 1

What does penicillin inhibit?

Answer 1

Cell wall peptidoglycan synthesis

Question 2

What happens when disruption of the peptidoglycan wall occurs?

Answer 2

Osmotic lysis of the bacterium

Question 3

What causes ‘Hotspot’ in dogs?

Answer 3

Staphylococcus

Question 4

Beta lactam antibiotics …

Answer 4

Contain a beta lactam ring in their molecular structures. Inhibits cell wall biosynthesis in the bacterial organism.

Beta lactams are hydrophilic, they do not like crossing membranes.

Question 5

Targeting bacterial peptidoglycan is an example of what?

Answer 5

Selective Toxicity

Question 6

What is the most commonly used beta-lactamase inhibitor?

Answer 6

Clavulanic acid eg amoxycillin

Question 7

Beta-Lactam Antibiotics

What are natrual penicillins predominatly active against?

Answer 7

Gram +ves and anaerobes, but some very important gram -ves also

incl pasteurella, streptococcus, and clostridia

Question 8

Beta-Lactam Antibiotics

What are aminopenicillins active against?

Answer 8

predom G+ve & anaerones, some important G-ve’s

Same as penicillin, but with better penetration (pKA related) into tissues/bacteria. eg amoxycillin.

Question 9

Beta-lactam Antibiotics

What are first gen cephalosporons active against?

Answer 9

Gram +ive, successive generations have increased activity against Gram-negative bacteria.

Question 10

Beta-Lactam Antibiotics

Why does first gen cephalosporins have excellent activity against staphylococcus

/

Answer 10

B-lactam ring is structually resistant to B lactamase.

Question 11

Beta-Lactam Antibiotics

Third gen cephalosporins active against?

Answer 11

Further improved gram neg but reduced gram pos activity.

Question 12

What is the t1/2 of B-lactams?

Answer 12

approx 1hr

Question 13

How safe is B-lactamans in regards to toxicity and what can it be used in?

Answer 13

Verysafe.

Geriatrics, juveniles, pregnancy and during lactation.

Question 14

What are the side effects of B-lactams and how do they come about?

Answer 14

Usually come about through a dysbiosis

• killing good bacteria
• recolonisation by a monomorphic population
• toxins
• GIT signs

Diarrhoahea, vomitting most common side effects

Question 15

A bit about Procaine Penicillin?

Answer 15

• Kills streptococcus, clostridia and pasteurella
• Excellent anaerobic efficacy
• Does not work against b-lactamase producing bacteria
• Convient dosing (sid)
• Never IV
• Low LD50 esp in horses
• Prescribed commonly

Question 16

What is the procaine used for in penicillin?

Answer 16

An insoluble salt

Question 17

What can procaine do to a horse’s brain?

Answer 17

Inhibits neural conduction in inhibitory inter-neurons

Question 18

A bit about amoxicillin - clavulanic acid

Answer 18

• excellent anaerobic efficiacy
• works against b-lactamase producing bacteria
• convient dosing (sid or bid)
• good distribution to most tissues
• not good for abcesses, pneumonia and mastitis
• Never IV

Question 19

What happens if you give a small animal oral beta lactam?

Answer 19

Destroys normal gut flora, overgrowth of clostridum difficile, toxin production.

Question 20

Give a summary of Aminoglycosides

Answer 20

• 30S ribosome target
• Gram neg mostly
• Doesnt kill anaerobes
• SID dosing
• Synergy with b-lactams
• Poor oral absorption
• Vestibular ototoxicity
• Nephrotoxicity

Question 21

What is one of, if not the most commonly used antibiotic classes for production animals?

Answer 21

Tetracyclines

Question 22

What is the mechanism of action of the ocytetracycline?

Answer 22

Binds to ribosomes and inhibits protein synthesis

Question 23

A bit about tetracyclines?

Answer 23

• broad spectrum
• long t1/2 (12hrs)
• excellent distribution
• 50:50 hepatic: renal metabolism
• out of date solutions are toxic
• large animal use mostly

Question 24

Name the two classes of beta lactams

Answer 24

1. penicillins
2. cephalosporins (more resistant to breakage)

Question 25

Who is more susceptible to beta lactams and why? gram +ve or gram -ve?

Answer 25

* gram +ve more susceptible as more peptidoglycan and not as well protected * Gram -ve has more membrane so better protected. cell wall double lipid membrane structure, porins less permeable to BL.

Question 26

What do beta lactamases do? | (enzymes present in resistant bacteria)

Answer 26

hydrolyse beta-lactam ring (except cephalosporins)

Question 27

How do beta-lactamase inhibitors work? MOA

Answer 27

* Use a second beta-lactam that will bind (preferrentially as greater affinity for enzyme) to the beta-lactamase * and therefore spare the first (and more clinically efficacious) beta-lactam

Question 28

Describe the pharmacokinetics of b-lactams

Answer 28

* hydrophilic * weak acids * good distribution except in pneumonic lung and absceses (abscess due to acidic enviro) * renal elimination