Session 4- antimicrobials

Question 1

What is a protozoa?

Answer 1

Single celled eukaryote

Question 2

Types of antimicrobial

Answer 2

Antibacterials
Antifungals
Antiprotozoals
Antivirals

Question 3

How can you classify antibacterials?

Answer 3

By their

• mechanism of action
• spectrum (broad/narrow)
• chemical structure
• kill/ inhibit growth and replication (bacteriostatic vs bactericidal)

Question 4

3 ways of measuring antibiotic activity

Explain each

Answer 4

• Disc sensitivity
• MIC, broth microdilution
• MIC, E test (slow)

Disc loaded with antibiotic is placed in on an inoculated agar plate and the zone of inhibition/ clearance measured. (Larger diameter= more antibiotic inhibition).

Minimum inhibitory concentration. Concentration of antibiotic is doubled each time until no bacterial growth occurs.

E- test; strip contains an antibiotic gradient and is placed on an inoculated agar. Circumference of zone of clearance begins from the MIC

Question 5

Which 3 types of antibiotic inhibit protein synthesis?

Give an example of each

Answer 5

• Tetracyclines (doxycycline)
• Aminoglycosides (Gentamicin)
• Macrolides (erythromycin)

Question 6

Tetracyclines: 
Mechanism 
Use
Adverse effects 
Example

Answer 6

Inhibit protein synthesis
Used as an alternative to penicillin in gram positive infection
Causes staining to developing teeth so no children < 12 or pregnant women
E.g. Doxycycline

Question 7

Gentamicin:
Type of antibiotic
Mechanism 
Use 
Adverse effects

Answer 7

Aminoglycoside
Inhibits protein synthesis

Endocarditis
Severe gram negative sepsis

Can be nephrotoxic and ototoxic

Question 8

Erthromycin:
Type of antibiotic
Mechanism
Use

Answer 8

Macrolide
Inhibits protein synthesis
Alternative to penicillin against gram positive infection

Question 9

Two types of antibiotic which inhibit cell wall synthesis?

Examples

Answer 9

• Beta lactams;
  Penicillins (flucloxacillin)
  Cephalosporins (ceftriaxone)
  Carbapenems
• Glycopeptides (vancomycin)

Question 10

Antibiotics used for meningitis and why?

Answer 10

Empirical ceftriaxone
Penicillin G/ Ampicillin
Bc both pass inflamed BBB and have action in CSF

Question 11

What does flucloxacillin treat?

Answer 11

Cellulitis- caused by Staphylococcus Aureus/ Streptococcus Pyogenes

Question 12

Penicillin is mainly active against ___?

Answer 12

Gram positives-
Staphylococcus
Streptococcus (especially)

Question 13

Carbapenems:

Type of antibiotic
Mechanism
Use
Example

Answer 13

• Beta lactams (others are penicillins and cephalosporins)
• Inhibits cell wall synthesis
• Reserve for gram negative infections (+ penicillin allergy)
• imipenem

Question 14

Vancomycin:

Type of antibiotic
Mechanism
Use
Features

Answer 14

• Glycopeptide
• Inhibits protein synthesis (along with tetracyclines and macrolides)
• MRSA & serious C .difficile (oral). Gram positives.
• Poor oral absorption so use IV or IM usually. Narrow therapeutic index so needs TDM, therapeutic drug monitoring.

Question 15

Is clostridium difficile gram positive or negative?

Answer 15

Gram positive and spore-forming

Question 16

Antibiotics which inhibit nucleic acid synthesis? (3)

How do they do this?

Answer 16

• Quinolones (Ciprofloxacin)
  Inhibit DNA gyrase (relaxes the supercoil in transcription)
• Rifampicin
  Inhibits bacterial RNA polymerase
• Trimethoprim (UTI) + Sulphonamides
  Inhibit folate synthesis

Question 17

Quinolones:

Mechanism
Use
Adverse effects
Example

Answer 17

• Inhibit nucleic acid synthesis (through inhibition of DNA gyrase)
• Against gram negatives
• Aortic dissection, tendinitis and rupture, plus CNS effects
• ciprofloxacin

Question 18

What do Azoles and Polyenes do?

Examples

Answer 18

Antifungals (fungistatic)
Azoles inhibit cell membrane synthesis
Polyenes inhibit CM function

- Azoles 
fluconazole (candida)
itraconazole (aspergillus)
- Polyenes 
nyastatin (topical for candida)
Amphoteracin (IV systemic fungal infection- aspergillus)

Question 19

Antifungals for aspergillus?

Answer 19

Itraconazole (azole)

I.V. Amphoteracin if systemic (type of polyene)

Question 20

Acyclovir:

What is it?
Mechanism
Uses

Answer 20

Anti viral agent
Prevents DNA synthesis (inhibition of DNA polymerase when phosphorylated)

Varicella zoster virus- Chicken pox, shingles,

Herpes simplex virus- genital herpes, encephalitis

Question 21

What is encephalitis?

Which infection causes it?

Answer 21

Inflammation of the brain caused by Herpes Simplex virus

Question 22

What does Varicella Zoster virus cause?

Medication?

Answer 22

Chicken pox and shingles

Acyclovir

Question 23

What does Herpes Simplex virus cause?

Answer 23

Genital warts and encephalitis

Question 24

Tamiflu;

What is it?
Mechanism
Uses

Answer 24

Also know as oseltamivir, it’s an antiviral agent
Inhibits viral neuraminidase in flu so the newly formed virions cannot be released into the blood stream (viral replication stops)
Influenza A and B

Question 25

What does neuraminidase enzyme do?

Answer 25

Cleaves the sialic acid residues to break the glycosidic linkage between the new virion and host cell enabling release into the blood stream (to further infect cells)

Question 26

What's special about metronidazole?

Answer 26

It's antibacterial (anerobic bacteria) AND antiprotozoal (eukaryotic)

Question 27

Amoebae Giardia Trichomonas are all types of what? What can you treat them with?

Answer 27

Protozoa G and T are parasites Metronidazole

Question 28

Amoebae Giardia Trichomonas What do they cause?

Answer 28

Dysentery (inflammation of intestines causing bloody diarrhoea) Diarrhoea Vaginitis / trichomoniasis (STI)

Question 29

Use of trimethoprim

Answer 29

UTI

Question 30

How do sulfonamides work? | How does trimethoprim work?

Answer 30

Sulfonamides inhibit de novo synthesis of folate in bacteria Trimethoprim inhibits conversion of dihydrofolate (DHF) to tetrahydrofolate (THF) in bacterial but not human cells.

Question 31

Why do we need folate?

Answer 31

To synthesise DNA nucleotides we (and bacteria) require enzymes which use co-factors deriving from folate. Specifically the derivative THF, tetrahydrofolate, is critical to enzyme activity

Question 32

List some mechanisms of bacterial antibiotic resistance

Answer 32

Reduced uptake Mutation of target site Down regulating expression of target site Increased efflux Enzymes which inactive the drug. E.g. beta lactamases inhibit beta lacta drugs

Question 33

Types of bacterial resistance? (3)

Answer 33

Innate Acquired- gain new DNA, usually permanent Adaptive- response to a stress like sub-inhibitory level of antibiotic; can be reversible

Question 34

Protective mechanisms against infections in the lungs? (Innate immunity)

Answer 34

Mucociliary clearance Coughing IgA (immunogolbulin of mucous membranes) Alveolar macrophages Antimicrobial proteins; - lysozyme (breaks bacterial cell walls) - lactoferrin (bacteriocidal; associated with mucus)

Question 35

Dyspnea?

Answer 35

Shortness of breath

Question 36

What is co-amoxiclav? | When is it used?

Answer 36

Combination drug which includes a beta lactam drug (amoxicillin) and a beta lactamase inhibitor - In community acquired pneumonia when the bacteria is resistant to amoxicillin (produce beta lactamases). E.g. Haemophilus Influenzae. - Or in severe pneumonia caused by Streptococcus Pneumoniae.