General Principles of Clinical Usage

Question 1

What are the 4 main patient characteristics that must be taken into account when administering drugs?

Answer 1

Age
Renal Function
Liver Function
Pregnancy

Question 2

Why must age be taken into account?

Answer 2

Children may have certain contraindications, compared to adults.
- For example: ciprofloxacin is not given, assumed to affect developing cartilage)

Question 3

Why is renal function taken into account?

Answer 3

• Antimicrobials are excreted by kidneys.
• So can accumulate in body during renal failure
• Meaning antimicrobial doses would need to be decreased in relation to the degree of renal insufficiency.

Question 4

Why is liver function taken into account?

Answer 4

• Antimicrobials may be metabolised in the liver and excreted in bile.
• Dose should be decreased in hepatic insufficiency or an alternate drug chosen if possible.

Question 5

Why is pregnancy an important factor in deciding drugs?

Answer 5

• Some antimicrobials may be contraindicated in pregnancy (may be mutagenic, teratogenic or both)
• Some may be contraindicated because their impact on the foetus is simply not known.

Question 6

What is prophylaxis?

Answer 6

Administration of the antimicrobials to prevent future occurrence of the infection.

• When patient has been exposed to a highly communicable disease.
• When patient is about to be subjected to surgical procedures with high post-op infection rates, such as bowel/abdominal surgery.

Question 7

What must be taken into account if the cause of infection is not known and urgent treatment is required?

Answer 7

• Take into account the site and type of infection –> the likely causative organisms and what the organism is likely to be susceptible too.
• Treatment should always be reviewed once results of culture and antimicrobial sensitivity test become available.

Question 8

What must be considered about the spectrum of the antimicrobial agent being administered?

Answer 8

• Should be effective against know or likely causative organism. (ideally following sensitivity tests once the organism has been isolated) - Sometimes an educated best must be made.

Question 9

Why is it best to sometimes use antimicrobials in combination?

Answer 9

• To cover mixed infection by more than one organism.
• Two antimicrobials can have an enhanced effect together.
• To minimise the development of resistant strains to any one agent.

Question 10

What are the three possible outcomes when a combination of antimicrobials are used?

Answer 10

• Effects are additive
• They are antagonistic (combined effects lesser that sum of individual effects)
• They are synergistic (combined effect is greater than the sum of their individual contributions).

Question 11

What are some general rules in terms of combination use of antimicrobials?

Answer 11

• Combination of two cidal drugs or of two static drugs is additive or synergistic.
• One static and one cidal may result in antagonism.

Question 12

What is one of the most important consideration about antimicrobials?

Answer 12

Penetration of the site of infection.

Question 13

What is a low therapeutic index?

Answer 13

• Difference between therapeutic and toxic dose is small.

Question 14

How are doses and durations of therapy decided?

Answer 14

In relation to the British National Formulary/Grampian Formulary.

• Serious infection may required higher doses than usual (consult pharmacist if this is case)
• Renal failure may need lower doses