Antimicrobials

Question 1

List the 3 types of Antibiotic Resistance

Answer 1

• Multi-drug Resistant (MDR)
• Extensively-drug Resistant (XDR)
• Pan-drug Resistant (PDR)

Question 2

How do the Beta-lactam antibiotics work?

List 3 types

Answer 2

• Interfere with the synthesis of the cell wall (peptidoglycan)
• Penicillins
• Cephalosporins
• Carbapenems

Question 3

What is Beta-lactamase?

Name a Beta-lactamase resistant drug

Answer 3

• Enzyme used by some bacteria to break down Beta-lactam Antibiotics
• Flucloxacillin

Question 4

Why is Clavulanic Acid added to Amoxicillin to produce Co-amoxiclav?

Answer 4

Clavulanic Acid is a Beta-lactamase Inhibitor

Thus inhibits bacterial action of Beta-lactamase

Question 5

What kind of Antibiotics are;

• Cefalexin
• Ceftriaxone
• Cefuroxime
• Cefotaxime

Answer 5

Cephalosporins (a type of beta-lactams)

Question 6

List 4 types of Antibiotic that interfere with Protein synthesis

Answer 6

• Tetracyclines (prevent tRNA binding to Ribosomes)
• Aminoglycosides
• Macrolides
• Nitrofurans

Question 7

Tetracyclines can be used in treating Respiratory infections, Acne, Chlamydia and Lyme disease

Why shouldn’t they be given to Children <12, Pregnants and Breastfeeding women?

Answer 7

Cause staining of developing teeth

Question 8

List 3 Macrolides

Answer 8

• Clarithromycin
• Erythromycin
• Azithromycin

Question 9

List common features of Pencillins and Macrolides

Answer 9

• Individual sensitivity testing required

- Similar clinical applications (Macrolides are also active against aytpical respiratory organisms)

Question 10

List 7 common clinical applications of Macrolides and Penicillins

Answer 10

• Bacterial Meningitis
• Bone/ Joint infections
• Skin/ Soft tissue infections
• Otitis Media
• Pneumonia
• UTIs
• STIs

Question 11

Describe why Nitrofurantoin is one of the 1st line treatments for UTIs?

Answer 11

• Up to 50% of an oral dose of Nitrofurantoin is excreted in urine in an unchanged form
• Allows Nitrofurantoin to concentrate in urine, increasing its effectiveness in the bladder (compared to other tissue compartments)

Question 12

How do Quinolones work?

Name 2

Answer 12

• Inhibit Topoisomerase II (Bacterial DNA Gyrase), the enzyme permits Transcription/ Replication
• Ciprofloxacin
• Levofloxacin

Question 13

Quinolones often require individual sensitivity testing.

List their clinical applications and antimicrobial properties

Answer 13

• Complicated UTIs
• Gonorrhoea
• Pseudomonas aeruginosa cover
• Very good cover of Gram(-ve)s as well atypical organisms and Gram (+ve)s

Question 14

List ADRs of Quinolones

Answer 14

• Tendinitis +/- rupture
• Aortic dissection (Aortic aneurysm bursts)
• CNS effects (E.g Convulsions)

Question 15

Sulfonamides are a type of AB that interfere with Folate Synthesis/ Action.

State another AB agent that acts in the same way
How does it work?

Answer 15

• Trimethoprim

- Folate antagonist, reversibly inhibits Dihydrofolate Reductase (stronger affinity for Bacterial DHFR than human)

Question 16

State the clinical application for Trimethoprim

List an ADR

Answer 16

• UTIs

- Teratogenic effects on fetus (so caution when prescribing to females of reproductive age)

Question 17

Why must patients avoid drinking alcohol when using Metronidazole?

Answer 17

Has Disulfiram-like action

build up of Acetaldehyde so hangover effects

Question 18

Why is Acyclovir predominantly activated in infected cells?

How does it work?

List 2 clinical applications

Answer 18

• The viral enzyme Thymidine Kinase is more effective at phosphorylating and thus activating it
• Fully phosphorylated form inhibits viral DNA Polymerase
• Herpes simplex infections (Genital herpes, Encephalitis)
• Varicella Zoster (Chicken Pox, Shingles)

Question 19

Herpes Simplex Virus (HSV) has 2 serotypes.

Compare their presentations

Answer 19

HSV1: Mouth/ lips/ eye infections

HSV2: Genital infection

Question 20

Describe the use of Acyclovir to treat Oral herpes (HSV1)

Answer 20

• Do NOT prescribe Topical Antivirals (limited evidence supporting use)
• NICE DOES NOT recommend routine prescription of Oral Antivirals for healthy people with Herpes Labialis

Question 21

Describe the use of Acyclovir to treat Genital herpes (HSV2)

Answer 21

1st episode;
- Oral Acyclovir within 5 days of start of episode OR while new lesions forming

Recurrent episodes;

• Episodic Antiviral treatment (Attacks infrequent at <6/year)
• Suppressive Antiviral treatment (Attacks frequent/ causing psychological distress/ affecting social life)

Question 22

How does Metronidazole affect Warfarin metabolism?

Answer 22

Inhibits CYP2C9-> Reduced metabolism of Warfarin so greater effect

Question 23

Verpamil and Simvastatin are metabolised by CYP3A4.

How do Macrolides affect their levels?

Answer 23

Macrolides inhibit CYP3A4 so increased effect

Question 24

Describe Enterohepatic Circulation/ Recycling

Answer 24

• Drugs absorbed in intestines and taken into hepatocytes

- Drug/ metabolites secreted into bile and returned to intestine where more drug is absorbed into circulation

Question 25

How do lower rates of Enterohepatic Recycling affect oral contraceptive effectiveness? How do oral ABs play a role in this?

Answer 25

- Lower EHR rates-> Lower blood concentrations of Oestrogen/ Progesterone-> Increased risk of getting pregnant - Oral ABs reduce gut flora-> Lowered EHR rates