9.1 Antimicrobial Chemo- prescribing principles

Question 1

Why would you think about prescribing antibiotics?

Answer 1

Therpay with/without direction

Prophylaxis- priamry, antimalairal, immunosupperssed, pre operative surgery, post exposure
Secondayr- to prevent a secodary exposure e.g. PJP

Question 2

How do you diagnose an infection?

Answer 2

Clinical signs, lab work, screening e.g. qSOFA

Question 3

What are important patient characteristics to think about before prescribing?

Answer 3

Age
Renal function
Liver function
Immunocomprimised
Pregnancy
Known allergies

Question 4

How do you select what antimicrobial to use?

Answer 4

Guideline or individualised therapy
? likely organism
empirical therapy or results based therapy
Bactericidal vs bacteriostatic drugs
Single agent or combination
Potential adverse effects

Question 5

What drug shoudl you use in an elderly woman with postural hypotnsion and e.coli in urin

Answer 5

First of all I wouldn’t treat, use Nitrofurantoin over trimethoprim as its given orally and well tolerated

Question 6

What are the four main mechanisms antibiotics use for resistance

Answer 6

Enzymatic inactivation of drug
Modified targets for drugs
Reduced permeability to drugs
Efflux of drug

Question 7

What is chromosomally mediated resistance?

Answer 7

Mutation in gene coding for drug target membrane transport system
Lower frequency of mutation for people who acquire plasmids
Less of a problem clinically
Basis for using multi-drug therapy e.g. TB

Question 8

What is plasmid mediated resistance?

Answer 8

Plasmids are extra-chromosmal strands of DNA
Replicate independent of cell chromosome
Carry genes for enzyme which degrade antibiotics and modify membrane transport systems
May carry 1 or more resistance genes

Question 9

What are the medically important resistant organisms

Answer 9

MRSA
VRE
ESBL
CPL
Clostridium difficile

Question 10

What is MRSA?

Answer 10

Resistant to flucloxacillin, often colonsies without infection, causes severe infections including osteomyeitis, endocarditis

Question 11

What is VRE?

Answer 11

Vancomycin resistant enterococci. Enterococci and intrinsically only sensitive to a limited number of antibiotics, VRE only sensitive to 1 or 2. Grow in the gut of patients exposed to multiple antibiotics, may cause invasive disease in patients with prosthetic devices

Question 12

What is ESBL?

Answer 12

Extended spectrum presenting beta-lactamase

Confer a range of resistance mechanisms, resistant to beta lactams, also may be reisstant to aminoglycosides and cabapenems

Question 13

What influnces antibiotic resistance?

Answer 13

Antibiotics used by medical professions, veterinary practices, farming. Patietns survivng longer with mroe medical conditions and hospital contact.
More invasive procedures and prosthetic devices

Question 14

What would you prescribe to someone who has cellulitis (typically caused by strep. pyogenes, staph aureus, strep. group C or G)

Answer 14

Fluxcloxacillin

Question 15

What is the go to drug for penicillin resistance?

Answer 15

Vancomycin

Question 16

What are the different types of hypersensitivty reactions that antibiotics can induce?

Answer 16

Type I- IgE meiated specific immunoglobulin, stimulates bronchospams/circulatory collapse

Type II- beta lactam specific IgG or IgM antibodies bind to circulating blood cell resultin in haematological reactions or interstitial nephritis

Type III- IgG or IgM bind to b-lactam antigens resulting in fever and sickness

Type IV- not antibody mediated but T cells recognise antigen leading to localised inflammation

Question 17

Someone presents with a staph aureus in surgical wounds, what do you treat it with?

Answer 17

Flucloxacillin

Question 18

Why might drug therapy fail?

Answer 18

Inadequate dosing
Inappropriate route
Non-compliance with antibiotics
Bacteria walled off in ascess cavity
Foreign bodies e.g. surgical implant
Poor penetration of drug to infection site e.g. bone and brain

Question 19

What antibiotics have good biofilm activity?

Answer 19

Rifampicin
Daptomycin
Ceftobiprole

Question 20

What is meant by the term antibiotic stewardship?

Answer 20

using the right antibiotic for the right indication for the right duration of time
Use an antibiotic only if suspected or proven bacterial infection
Use antibiotics as per guidelines and review with results of microbiology
Review antibiotic prescriptions regularly
Limit use of broad spectrum blind antibiotic therapy

Question 21

When would you consider switching someone from IV to Oral antibiotics

Answer 21

After 48 hours symptoms are improved and the patient can:
Swallow and tolerate fluids
Temp 36-38 for at least 2 days
Heart rate <100 bpm
WCC between 4 and 12

Question 22

When would you NOT switch antibiotics from IV to oral?

Answer 22

Compromised oral route-diarrhoea, vom, NBM
Continuing sepsis
Special indications- endocarditis, meningitis, staph aureus bactermia, immuno suppression, bone/joint infection, deep abscess, CF, prosthetic infection)